ATHENA OpticMin © Pierre Perroud (2016): Search common rock forming minerals from optical properties observed with the petrographic microscope

Pierre Perroud, Susanne Theodora Schmidt, Annette Süssenberger

Plates are part of the "Atlas of rock-forming minerals (transmitted light)" by Susanne Theodora Schmidt, University of Geneva, 108 p
Plagioclase calculation module by Christian de Capitani, University of Basel.

I wrote OpticMin for my own use: you may use it at your own risk. You are welcome to send corrections and suggestions.
Version: see update date at the bottom of the page

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This multiple search table helps to rough out the study of exercise thin plates. Here are some of the most common rock-forming minerals. They represent about 90% of the rock forming minerals. There are more than 5000 mineral species (end 2015); if your mineral is uncommon you will not find it here. See bibliography at the bottom of the page: books and publications are irreplaceable to go deeper into your search results and ascertain them. If you use this search table, please contribute with sending corrections and comments.

Columns

Columns and data have been strongly compressed to fit page width. Columns are sortable. Data are for standard thin sections (standard thickness, fresh polished, unstained), correct illumination, etc. (see manuals in the bibliography below).
01. Mineral. Mineral name, or group, or series (According to H. Strunz).
       Formula. Formula and references can be found here: Athena. Some names are redundant (e.g. mineral name and group name) to make search easier.
02. Color. Color in thin section PPL (plane polarized light). Search suggestions: colorless, blue, pinkish, etc.
       Pleochroism. Search suggestions: Pl., weak, distinct, strong, color names
03. Form. Habitus. Irregular forms and grains are not mentioned.
04. Cleavage. Search suggestions: perfect, good, distinct, poor, a form symbol (e.g. {110}, etc.), //, basal, parting
05. Twinning. Search suggestions: a twinning name (e.g. Carlsbad, etc.), simple, lamellar, polysynthetic, //, a form symbol (e.g. {110}, etc.)
06. Extinction angle. Search suggestions: symmetrical, //, basal.
       Elongation sign: length slow (positive elongation), length fast (negative elongation).
07. Birefringence. Δn=(ne-no) or (nz-nx). Search suggestions: 1st, 2nd, 3rd, 4th, 5th, high upper order.
       michel_levy.jpg
08. Relief. Positive when R.I mineral is greater than the R.I. of the mounting material (~1.54). Negative when R.I. mineral is lower.
       Search suggestions: H(-), M(-), L(-), L(+), M(+), H(+), VH(+). Values are from W. Nesse: H(-) <1.42; M(-) 1.42-1.50; L(-) 1.50-1.54; L(+) 1.54-1.58; M(+) 1.58-1.66, H(+) 1.66-2.00, VH(+) > 2.00 .
       R.I.: Refractive Indices. isotropic: n; uniaxial: ne, no (=nε, nω); biaxial: nx, ny, nz (= nα, nβ, nγ). You should verify; they are not exactly the same from one book to another. You can try with rough data: 1.5, 1.6, etc.
09. Indicatrix (Interference figure and optical sign). Conoscopy. Search suggestions isotropic, U(+), U(-), B(+), B(-).
       System. Search suggestions: cubic, tetragonal, trigonal, hexagonal, orthorhombic, monoclinic, triclinic.
10. 2V angle: B+ when 2Vz (=2Vγ) is acute; B- when 2Vx (=2Vα ) is acute. 2V examples.2V angle
       Dispersion. Search suggestions: r>v, r<v, weak, moderate, strong
11. Occurrence. Paragenesis. Alteration. This column is obviously very incomplete.

1. Use a large screen, high-definition.
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4. Enter your query (anything: name, color, form, etc.). You can use truncated words (e.g. 'twin' will find 'twins', 'twinning', etc.). Avoid using numbers (Δn, R.I., 2V, etc.): you cannot search within a range.
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Mineral name. FormulaColor PPL. PleochroismForm. HabitusCleavageTwinningExtinction. ElongationBirefringenceRelief. R.I.(± 0.002)Indicatrix. System2V angle. DispersionOccurrence. Paragenesis. Alteration

Mineral,FormulaColor ppl,PleochroismForm,HabitusCleavageTwinningExtinction,ElongationBirefringenceRelief,R.I.(± 0.002)Indicatrix,System2V,DispersionOccurrence,Paragenesis,Alteration
ACTINOLITE
[]Ca2(Mg,Fe++)5Si8O22(OH)2
(Inosilicate. Clinoamphibole, Tremolite - Actinolite - Ferro-actinolite series.)
photo
Pale yellow green, blue green to dark green. Color increases with Fe content.
Pl. X= colorless, pale yellow green, Y= pale yellow green, pale blue green, green Z= pale green, green, blue-green, dark green
Prismatic, columnar, bladed, acicular, fibrous. Rhombic basal section.{110} intersects at 56° and 124°. Visible on basal sections.
Parting on {100} and {010} (rare)
Simple or {100} lamellar, // to the long diagonal of the basal sectionInclined ext. 10°-17°
Sections // to (100) show // extinction
Length slow.
Δn=0.017-0.022
Upper 1st order to mid 2nd order.
M(+) to H(+)
nx=1.620-1.670
ny=1.630-1.675
nz= 1.645-1.688
R.I. increases with increasing Fe content.
B(-)
Monoclinic
2Vx=74°-84°
r<v weak
Low grade metamorphic rocks. Meta-basalts, meta-gabbros, with chlorite.
With calcite, dolomite, forsterite, garnet, diopside, wollastonite, talc, epidote. Also in metamorphic mafic, ultramafic rocks. In blue schists.
Altered to chlorite, talc, carbonates.
AEGIRINE
NaFe+++Si2O6
(Inosilicate, sodic clinopyroxene; sometimes named acmite)
Bright green to yellow green.
Pl. X= emerald green, deep green, Y= grass green, yellowish green, yellow, Z= brownish green, green, yellowish brown, yellow.
Stubby prismatic, elongated columnar xlsIntersects 87° in (110)
Parting {001} and {100}
Octagonal sections show 87° cleavages.
Simple and lamellar on {100}Inclined ext. 0°-10° in (010)
Basal section: symmetrical ext. (110)
Δn=0.045-0.060
3rd order
H(+)
nx=1.750-1.776
ny=1.780-1.820
nz=1.795-1.836
B(-)
Monoclinic
2Vx=60°-70°
r>v moderate to strong
In alkaline igneous rocks: alkali granite, syenite, nepheline syenite. In carbonatites, glaucophane schists.
Altered to amphibole (uralite), chlorite
AEGIRINE-AUGITE
(Ca,Na)(Mg,Fe++,Fe+++)Si2O6
(Inosilicate, sodic-calcic clinopyroxene)
photo
Pale green to yellow green.
Pl. X= bright green, deep green, brownish green, Y= yellowish green, Z=yellow, greenish brown, brownish green. Color zoning, dark rim.
Stubby prismatic, elongated xls. Octagonal sections show 87° cleavages.Intersects 87° in (110)
Parting {001} and {100}
Simple and lamellar on {100}Inclined ext.: 0°-20° in (010)
Basal section: symmetrical ext. (110)
Δn=0.030-0.053
2nd order to lower 3rd order
H(+)
nx=1.700-1.760
ny=1.710-1.800
nz=1.730-1.813
B(-) or B(+)
Monoclinic
2Vx=70°-110°
r>v moderate to strong
In alkalic igneous rocks with sodic amphiboles, K-feldspars and nepheline: alkali granite, quartz syenite, nepheline syenite.
In sodic volcanic rocks: peralkaline rhyolites
In carbonatites, glaucophane schists.
Altered to amphibole (uralite), chlorite
AENIGMATITE
Na2Fe++5Ti++++Si6O20
(Inosilicate, aenigmatite - sapphirine - surinamite group)
Dark reddish brown, nearly opaque
Pl. X= light yellow brown, reddish brown, Y= reddish to dark chestnut brown, Z= deep reddish brown, brownish black, opaque
Long prismatic xls.{100} and {010} perfect{1-10} polysynthetic twins
Inclined ext.Δn=0.07
Very high upper orders, 4th order
(H+)
nx=1.81
ny=1.82
nz=1.88
B(+)
Triclinic
2Vz=32° (27°-55°)In Si-poor lava. In Na-rich magmatic rocks. Alkaline rhyolite, trachyte, phonolite. In nepheline and sodalite syenites. With aegirine-augite, arfvedsonite or riebeckite, anorthoclase and nepheline. Homoaxial intergrowth with arfvedsonite is common;
ALBITE, high
NaAlSi3O8
(Tectosilicate, plagioclase, An0-An10)
ColorlessPrismatic elongated laths in magmatic rocks, bladed.
Anhedral in metamorphic rocks.
{001} perfect, {010} good, {110} poorNon-twinned, simple and polysynthetic albite twins (010)
Pericline (h01)
polysynthetic. Carlsbad penetration.
Inclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.007-0.008. 1st order grey or white.
Optic related to anorthite content
L(-) to L(+)
nx=1.526-1527
ny=1.532-1.533
nz=1.534-1.541
Difficult to distinguish.
B(-)
Triclinic
2Vx=50°-54°
r>v weak
High temperature lavas.
Altered to kaolin, sericite
ALBITE, low
NaAlSi3O8
(Tectosilicate, plagioclase, An0-An10)
photo
Colorless, clouded (alteration)
Perthite: albite exsolutions in microcline or orthoclase
Tabular, // to (010), prismatic, elongated. Common chemical zoning.{001} perfect, {010} good, {110} poorNon-twinned, simple and polysynthetic albite twins (010).
Pericline (h01)
polysynthetic. Carlsbad penetration.
Inclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.011. 1st order grey or white.
Optic related to anorthite content
L(-)
nx=1.527
ny=1.531
nz=1.538
Difficult to distinguish
B(+)
Triclinic
2Vx=77°-84°
v>r weak
In plutonic rocks, granite, granodiorite, pegmatites, syenite. Hydrothermal veins (pericline). Volcanic: rhyolite. Low grade pelitic metamorphic
Altered to calcite, sericite, zeolites, muscovite, kaolinite, prehnite, pyrophyllite, epidote (saussurite)
ALUNITE
K2Al6(SO4)4(OH)12
(Sulfate)
photo
ColorlessTabular, square section, rhombic section, flaky, granular{001} Ext. // to cleav. {001}
Length fast
Δn=0.010-0.023
Increases with Fe
M(+)
no=1.572-1.620
ne=1592-1.641
U(+)
Hexagonal
 In altered volcanic rocks: Hydrothermal alteration of feldspars.

AMPHIBOLE
(Inosilicate. A supergroup name. Orthorhombic amph.: Anthophyllite, Holmquistite, Ferrogedrite, etc. Monoclinic amph.: Cummingtonite, Grunerite. Tremolite, Actinolite. Hornblende. Glaucophane, Riebeckite. Katophorite. Arfvedsonite. Richterite, Pargasite, Winchite, etc.)
General formula:
A0-1B2C5T8O22W2
A=Na,K,Ca,Li,[] (vacancy)
B=Na,Ca,Fe++,Mg,Mn++,Li
C=Mg,Fe++,Mn++,Al, Fe+++,Mn+++,Ti++++,Li
T=Si,Al,Ti++++
W=(OH),F,Cl,O--
photo  photo

Green, brown, colorless or blue). Typically paler amphiboles contain less Fe and more Mg. Pleochroic.
Glaucophane (blue-mauve, colorless).
Actinolite (colorless - blue green - green).
Tremolite (colorless).
Hornblende (green brown).
Amphibole forms typically well-shaped crystals in rocks with abundant quartz or plagioclase. Ideal crystal forms are prismatic elongated with rhombic-shaped or stretched hexagon cross section. In rocks with abundant Fe-Mg silicates amphibole typically is equant.Cross sections show two cleavages intersecting at ~120°. (56° and 124°) in {110} Inclined extinction (typically <30°)
Symmetric: basal section.
Parallel (100)
Δn=0.01-0.03
1st order to upper 2nd order
M(+) H(+)
From nx ~ 1.6 to nz ~ 1.8
B(+) or B(-)
Orthorhombic
Monoclinic
2V=very variable, 35° - 130°Plutonic, volcanic, metamorphic. Brown hornblende (basalt). Green hornblende (diorite, granite). Glaucophane (metabasalt, metagabbro). Actinolite rims around metamorphosed pyroxenes.
Glaucophane - Na-rich stable at low T and high P (blue schists). Tremolite - Mg-rich found in metamorphosed carbonates and peridotites. Actinolite – Fe-rich stable at moderate T in metamorphic rocks. Hornblende – Fe-Al-rich stable at high T in igneous rocks and high T in metamorphic rocks
Altered to: Chlorite (pale green). Commonly replaces: Clinopyroxene .
Distinguishing features: Biotite (one cleavage, // extinction; bird's eye polarization). Chlorite (green, low and anormal interference colors). Pyroxene (two cleavages at 90°, higher extinction angle, typically paler colored).
ANALCIME
Na[AlSi2O6].H2O
(Tectosilicate, zeolite, analcime group) (analcite: not IMA name)
photo
ColorlessTrapezohedrons. 8 sided sections, anhedral.{001} very poor{001}, {110}, lamellar Isotropic. Δn=0.001. Very weak. Lower 1st orderM(-)
n=1.479-1.493
Isotropic
Cubic
 In Si-deficient igneous rocks: syenite,Hydrothermal alteration of basalt
Altered to pseudoleucite, zeolites
ANDALUSITE
Al2SiO5
(Nesosilicate
sillimanite - andalusite - kyanite group)
photo
Colorless. Rarely pink or greenish with weak pleochroism. Pl. X= pink, Y=Z= greenish yellow, colorless. Colors uneven distributed. Color darker when Mn or Fe increase.Prismatic with square section. Cross dark inclusions in chiastolite formed by sericite and/or opaques minerals.2 good {110} cleavages nearly at right angle. Rarely visible.Twinning {101} rare// extinction
Symmetric extinction in basal sections.
Length fast
Δn=0.009-0.013. Often 1st order grey, white, yellow.M(+)
nx=1.629-1.640
ny=1.634-1.644
nz=1.638-1.650
Orthorhombic
B(-)
2Vx=71°-88°
r<v weak; rarely r>v
Contact and regional metamorphic rocks: hornfels, mica schist. Also in granite, pegmatite
With cordierite, staurolite, garnet, sillimanite, kyanite, chlorite, muscovite, plagioclase. Altered to sericite, chlorite
ANDESINE
(Na,Ca)[Al(Si,Al)Si2O8]
(Tectosilicate, plagioclase, An30-An50)
Colorless, clouded (alteration)Tabular, // to (010), prismatic elongated. Common chemical zoning in magmatic rocks. Anhedral in metamorphic rocks.{001} perfect, {010} good, {110} poorNon-twinned, simple and polysynthetic albite twins (010).
Pericline (h01)
polysynthetic. Carlsbad penetration.
Inclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.008. Low: 1st order up to grey
Optic related to anorthite content
L(+)
An40:
nx=1.549
ny=1.553
nz=1.557
B(+)
Triclinic
B(+) plutonic rocks
B(-) volcanic rocks
2Vx=83°
r>v weak
2V=78°-90° in plutonic rocks
2V=80°-100° in volcanic rocks
In felsic and intermediate igneous rocks Volcanic: andesite. Metamorphic medium and high grade.
Altered to calcite, sericite, zeolites, muscovite, kaolinite, scapolite, prehnite, pyrophyllite
ANHYDRITE
CaSO4
(Sulfate)
photo
Colorless
Rare weak violet Pl.
Prismatic, tabular, fibrous, radiating3 pinacoidal cleavages at right angle: {010} perfect, {100} good, {001} goodSimple on {011}Ext. // cleavages and xl faces. Acicular xls: // extinction.
Length slow if elongate on c
Δn=0.040-0.044
Vivid 2nd order colors
M(+)
nx=1.569-1.574
ny=1.574-1.579
nz=1.609-1.618
Orthorhombic
B(+)
2Vz=42°-44°
r<v distinct
In evaporites, with halite, sylvite, calcite, dolomite, gypsum, clay.
Hydrothermal. Volcanic amygdules
Altered to gypsum
ANKERITE
Ca(Fe++,Mg,Mn)(CO3)2
(Carbonate. Dolomite group)
Colorless, brownish (if iron oxides)Rhombohedral, also curved faces{10-11} perfect{02-21} lamellar
Simple: {0001}, {10-10}, {11-20}, {10-11}
Symmetrical or inclinedΔn=0.182-0.202
High upper order white or grey
L(-) L(+) M(+) H(+)
no=1.690-1.750
ne=1.510-1548
U(-)
Hexagonal, Trigonal
 In veins in Fe sediments with siderite and Fe-oxides. In schists with amphibole.
ANORTHITE
CaAl2Si2O8
(Tectosilicate, plagioclase, An90-An100)
Colorless, clouded (alteration)Tabular, // to (010), prismatic elongated. Common chemical zoning.{001} perfect, {010} good, {110} poorSimple and polysynthetic (010). Polysynthetic pericline. Carlsbad penetrationInclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.013. 1st order grey or white, up to yellow.
Optic related to anorthite content
L(+)
An100:
nx=1.577
ny=1.585
nz=1.590
R.I. decreases with Ab content.
B(-)
Triclinic
2Vx=75°-80°
v>r weak
Mafic rocks. Volcanic: basalt
Rare in metamorphic carbonate rock
Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite
ANORTHOCLASE
(Na,K)AlSi3O8
(Tectosilicate, K feldspar, Ab63-Ab90)
ColorlessPrismatic xls{001} perfect, {010} distinct intersect at ~92°Complex twinning according to albite and pericline laws. Polysynthetic on {010}
Ultra-fine cross-hatched twinning..
Inclined ext. 4°-10° on {001} cleavageΔn=0.006-0.007
1st order grey or white.
L(-)
nx=1.524-1.526
ny=1.529-1.5342
nz=1.530-534
R.I. increases with Na content.
B(-)
Triclinic
2Vx=42°-52°
r>v weak
In high temperature Na rich volcanic. rocks rhyolite, trachyte, phonolite.
Altered to kaolinite, sericite, cryptocrystalline silica
ANTHOPHYLLITE
[]Mg7Si8O22(OH)2
(orthoamphibole)
photo
Colorless, pale brown. Darker with higher Fe content.
Weak Pl. X= colorless, pale yellow, pale grey brown, pale greenish yellow, Y= colorless, pale grey brown, pale greenish yellow, Z= pale grey brown, purplish brown, grey green.
Prismatic columnar, bladed, acicular. Rhombic basal section{210} perfect, prismatic cleavages intersect at 55°-125° Symmetrical (basal).
// (longitudinal) ext. on {110} cleavage
Length slow.
Δn=0.013-0.028
1st order red (B+), 2nd order blue (B-).
M(+) to H(+)
nx=1.587-1.668
ny=1.602-1.670
nz=1.613-1.680
R.I. increases with increasing Fe content.
B(+) or B(-)
High Mg are B(-)
Orthorhombic
2Vx=65°-122°
Moderate, r<v (+), r>v (-)
Medium and high grade metamorphic: amphibolite, gneiss, granulite, hornfels, talc schist. With garnet, cordierite, hornblende, sillimanite, plagioclase.
Altered to serpentine, talc at low temperatures

APATITE
Ca5(PO4)3(F,OH,Cl)
(Phosphate. A group name: fluorapatite, hydroxylapatite, chlorapatite, etc., also with REE)
photo

Colorless (except for strong colored specimens).
Weak to moderate pleochroism, e>o.
Prismatic, elongated xls, hexagonal cross section.Poor {001}Rare// extinction
Length fast
Δn=0.001-0.007. 1st order grey.
Carbonate-apatite: up to lower 2nd order
M(+)
no=1.629-1.667
ne=1.624-1.666
U(-)
Hexagonal
B(-) with 2v<10°
 Igneous and metamorphic. In phosphatic limestone, shale, phosphate deposits. Hydrothermal.
ARAGONITE
CaCO3
(Carbonate)
ColorlessPrismatic, // or radiated aggregates{010} imperfect{110} produces pseudohexagonal formExt. //
Length fast
Δn=0.155
High upper order white
L(-) L(+) M(+) H(+)
nx=1.530
ny=1.680
nz=1.685
B(-)
Orthorhombic
2Vx=18° (up to 23° with increasing Pb)
v>r weak
Sedimentary. In hot springs.
Volcanic, in basalt, andesine, with zeolites
Metamorphic. In high pressure low temperature blue schist with glaucophane, crossite, lawsonite, In aegirine-albite rocks. In serpentine with dolomite, magnesite, brucite.
ARFVEDSONITE
NaNa2(Fe++,Mg)4Fe+++Si8O22(OH)2
(Inosilicate, clinoamphibole. Series arfvedsonite - eckermannite)
photo
Blue green, brown, violet to almost opaque. Absorption colors form deep Prussian blue to brownish green. Anomalous interference colors due to strong absorption. Pl. X= blue green, Y= light blue green, brown yellow, grey violet, Z= yellow green, blue grey, brownish green, blackBladed, prismatic, fibrous. Rhombic basal section.{110} intersects at 56° and 124°.
Parting on {010}
Simple or lamellar on {100}Symmetrical (basal).
// (100). Inclined on other longitudinal sections
Length fast.
Δn=0.005-0.012
Low, up to mid 1st order. Basal sections show low order.
H(+)
nx=1.62-1.70
ny=1.63-1.71
nz=1.64-1.71
B(+) or B(-)
Monoclinic
2Vx=0°-100°In alkaline igneous rocks and peralkaline volcanic rocks: alkali granite, syenite, trachyte, phonolite, pegmatite.
With aegirine, aegirine-augite, biotite, feldspar, nepheline.
Altered to amphibole (uralite), iron oxides, chlorite.
ARMENITE
BaCa2Al6Si9O30.2H2O
(Cyclosilicate. Milarite group)
ColorlessPrismaticPerfect prismatic. Distinct pinacoidalComplex showing triplets. Also lamellar. Partings along sector boundaries Δn=0.009-0.011L(+)
nx=1.550-1.551
ny=1.557-1.559
nz=1.559-1.562
B(-) with U(-) domains
Orthorhombic, pseudohexagonal
2Vx=60°-65°Associations: with axinite, pyrrhotite, quartz in calcite veins; albite, with Mn zoisite, piemontite, prehnite, epidote, muscovite in Mn metasomatized diorite; with celsian, margarite, quartz, zoisite, ganterite in gneiss
AUGITE
(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
(Inosilicate, calcic clinopyroxene)
photo
Colorless, grey, pale green, pale brown, brownish green. Titanaugite: purplish, brown, brown-violet. Color zoning: concentric, hourglass pattern. No or weak Pl. X= pale green, bluish green, Y= pale greenish brown, green, bluish green, Z= pale brownish green, green, yellow greenStubby prismatic xls. Basal section: 4 or 8 sided.{110} distinct, intersect at ~87°. Parting {001} and {100}{100} or {001} lamellar, both combined as herringbone patternBasal (2 cleavages) symmetrical ext.
// c: inclined 35°-48° on {110} cleavage
// (100) is length slow
Δn=0.018-0.034
Up to mid 2nd order.
Exsolved orthopyroxene lamellae.
H(+)
nx=1.671-1.735
ny=1.672-1.741
nz=1.703-1.761
R.I. increases with Fe content
B(+)
Monoclinic
2Vz=25°-70° increase with Ca content
r>v weak
r<v strong in Ti augite
Plutonic, volcanic and high grade meta-igneous
Igneous: gabbro, granodiorite, ultramafic, mafic. Volcanic: basalt, andesite. Metamorphic: amphibolite, gneiss, skarn. With tremolite-actinolite, grossular, epidote, wollastonite, forsterite, monticellite, calcite, dolomite. Altered to hornblende, amphibole (uralite), serpentine, chlorite, epidote, carbonates.
AZURITE
Cu3(CO3)2(OH)2
(Carbonate)
Blue.
Weak Pl. X=clear blue, Y=Azure blue, Z=dark blue, violet blue
Tabular, radiated{011} perfect, {100} fair, {110} poorRare. {-101}, {-102}, {001}Length slowΔn=0.106
High order cream white masked by mineral color
H(+)
nx=1.730
ny=1.756
nz=1.836
B(+)
Monoclinic
2Vz=68°In oxidized zone of hydrothermal Cu deposits
Replaced by malachite.
BARROISITE
[]{CaNa}{Mg3Al2}(AlSi7O22)(OH)2
(Inosilicate)
photo
       Monoclinic  
BARYTE
BaSO4
(Sulfate)
Colorless.
Weak Pl., pale colors
Tabular, prismatic{210} 2 very good, intersects at 78°
{010} good
Basal {001} intersects 3 others at 90°
{110}// Length slow
Basal: symmetrical ext.
Δn=0.012
M(+)
nx=1.634-1.637
ny=1.636-1.639
nz=1.646-1.649
B(+)
Orthorhombic
2Vz=36°-40°
r<v
In hydrothermal veins. Sedimentary rocks.
Altered to witherite
BERYL
Be3Al2Si6O18
(Cyclosilicate)
Colorless
Colored varieties with Pl. o<e
o= light blue, e= blue
or o= yellowish green, e= green
Elongated prismatic hexagonal. Basal sections: hexagonal. Longitudinal sections: rectangular{001} poorRare// ext. Length fastΔn=0.004-0.009L(+) M(+)
no=1.569-1.610
ne=1.560-1.599
U(-)
Hexagonal
 In granitic pegmatites with quartz, K-Feldspar, albite, muscovite, biotite, tourmaline. In granite, In nepheline syenite. High temperature hydrothermal with Sn and W minerals.
Altered to sericite, clay
BIOTITE
K(Mg,Fe++)3(Al,Fe+++)Si3O10(OH,F)2
(Phyllosilicate. A series name in the mica group)
photo photo
Brown, brownish green, reddish brown. Mottled interference colors Phlogopite is pale brown, colorless. Pleochroic halos around radioactive minerals
Strong Pl. X= colorless, pale yellow, light brown, greenish brown, pale green, Y=Z= brown, olive brown, dark green, dark red brown
Tabular, lamellar, bladed, hexagonal section. Bent during deformation.{001} perfect, thinRareExt . //, rarely inclined up to max. ~9°
Length slow: Wave extinction on bent grains.
(Amphiboles: inclined ext.)
Δn=0.028-0.07
Strong, 2nd order, 3rd order, 4th order.
Pebbly, birds-eye texture seen near extinction
L(-) L(+) M(+) H(+)
nx=1.530-1.625
ny=1.557-1.696
nz=1.558-1.696
R.I. increases with Fe content.
B(-)
Monoclinic
2Vx=0°-25°
Lepidolite: smaller 2V
r<v weak
(r>v Mg rich varieties)
Igneous rocks. Metamorphic rocks, phyllite, schist, gneiss, hornfels.
Phlogopite in ultramafic rocks, in metamorphosed carbonates
Altered to chlorite, vermiculite, calcite, Fe-Ti oxides
BRONZITE (En88-En70)
(Mg,Fe++)2Si2O6
(Inosilicate, orthopyroxene, Enstatite - Ferrosilite series)
(A ferroan enstatite)
Pale colored.
Pl. X= pink, brownish pink, pale yellow, Y= light brown, yellow, pinkish yellow, greenish yellow, Z= light green, grey green, bluish green
Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages
Exsolution lamellae (augite)
Good // {210}, intersect at ~ 88°. Exsolution lamellae (augite)
Parting on {010} and {001}.
Fine lamellar // {100} is often exsolution lamellaeExt. //
Basal: symmetrical
Cleavage trace length slow
Δn=0.011
1st order
H(+)
En80:
nx=1.677
ny=1.685
nz=1.690
B(-)
Orthorhombic
2Vz=50°-90°
r>v moderate
In charnockite, with diopside and hornblende.
BRUCITE
Mg(OH)2
(Hydroxide)
ColorlessFoliated, fibrous, flakes{001} perfect Ext. //
Length fast
Δn=0.010-0.021
Strong dispersion. Anomalous 1st order red brown or blue
M(+)
no=1.560-1.590
ne=1.580-1.600
U(+)
Hexagonal, Trigonal
 From alteration of periclase in marble
In serpentinite and chlorite schist, with talc, magnesite
Altered to hydromagnesite
BYTOWNITE
(Ca,Na)[Al(Al,Si)Si2O8]
(Tectosilicate, plagioclase, An70-An90)
Colorless, clouded (alteration)Tabular, // to (010), prismatic elongated. Common chemical zoning.{001} perfect, {010} good, {110} poorAlbite polysynthetic. Pericline polysynthetic. Carlsbad penetrationInclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.010. 1st order grey or white, up to yellow
Optic related to anorthite content
L(+)
An80:
nx=1.569
ny=1.574
nz=1.579
B(+) or B(-)
Triclinic
2Vx=87°-103°
v>r weak
In gabbro, anorthosite, mafic rocks. In stony meteorites.
Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite
CALCITE
CaCO3
(Carbonate, calcite group)
photo
Colorless, cloudy
Iridescence along cleavages.
Relief Pl.
Scalenohedrons, rhombohedrons, prismatic, spherulitic, etc.{10-11} perfect, . Intersects at 74°57'.
{01-12} parting
Some deformation twins (if present) bisect acute cleavage angle. (see dolomite)
{01-12} lamellar
{0001} contact
Extinction: inclined or symmetrical to cleavage faces.
Length slow
Δn=0.172
High upper order grey
M(-) L(-) M(+) H(+)
no=1.658
ne=1.486
U(-)
Hexagonal, Trigonal
 Ubiquitous. Sedimentary. Metamorphic, marble, with wollastonite, garnet, olivine, diopside, vesuvianite, tremolite, epidote. In igneous rocks with nepheline, feldspathoids. Hydrothermal.
Altered to dolomite, replaced by quartz, opal, Fe or Mn oxides
CANCRINITE
Na6Ca2Al6Si6O24(CO3)2
(Tectosilicate, cancrinite group)
ColorlessHexagonal prismsPerfect prismatic {100} 3 directions 60°, perfect
{001} poor
 // ext.
Length fast
(Microsommite is length slow)
Δn=0.002-0.025
Δn decrease as Na - SO4 replaces Ca - CO3
L(-) M(-)
no=1.490-1.528
ne=1.488-1.503
R.I. decrease as Na - SO4 replaces Ca - CO3
U(-)
Hexagonal
Microsommite is U(+)
 In nepheline syenite. With nepheline, calcite,sodalite, K-feldspars, melanite, wollastonite, corundum, K-pyroxenes, amphiboles. Vishnevite contains Na and SO4.
Replaced by calcite.
CELADONITE
K(Mg,Fe++)Fe+++(Si4O10)(OH)2
(Phyllosilicate, mica group)
photo
X = pale yellow green, Y=Z = dark green, blue greenScalesPerfect {001}  Δn=0.014 to 0.032nx=1.606-1.610
ny=1.610-1641
nz=1.610-1.641
B(-)
Monoclinic
2Vz=0° to 20°Altered volcanic rocks
CELESTINE
SrSO4
(Sulfate)
Colorless, pale blue, pale blue-green, pale violet
Weak Pl. blue, lavender, blue green, violet shades
Prismatic, elongated, tabular{001} perfect
2 good prismatic {210} intersect at 75°
{010} poor
 // ext on c and // to {210} cleavages
Length fast on c.
Δn=0.009-0.010
1st order grey, white, pale yellow
~0.002 birefringence on (100) section
M(+)
nx=1.621-1.622
ny=1.623-1.624
nz=1.630-1.632
B(+)
Orthorhombic
2Vz=51°
r<v
Sedimentary. Evaporites, with gypsum, anhydrite, halite. In limestone. Hydrothermal
CELSIAN
BaAl2Si2O8
(Tectosilicate, Ba feldspar)
ColorlessTabular, prismatic, elongated xls.{001} perfect, {010} distinct, intersecting at 90°. {110} poorSimple, Carlsbad, Manebach, Baveno.
No multiple twinning.
Inclined ext. max. 29° to {001} cleavageΔn=0.009-0.013
1st order grey, white or yellow.
M(+)
nx=1.579-1.587
ny=1.583-1.593
nz=1.588-1.600
B(+)
Monoclinic
2Vz=83°-90°Hydrothermal veins in rich Mn rocks. Granite gneiss.
With Mn minerals, rhodonite, rhodochrosite, spessartine
CHABAZITE
(Tectosilicate, zeolite, chabazite - levyne group)
(A series name: Chabazite-Ca, -K, -Mg, -Na, -Sr)
ColorlessRhombohedral with 93°-94° angles, ~ like cubes3 good cleavages on {101}Penetration and lamellar twins Δn=0.002-0.010
1st order grey
L(-) M(-)
no=1.478-1487
ne=1.480-1.493
U(+) U(-) B(+) B(-)
Triclinic, pseudohexagonal
2V=0°-32°In lacustrine sediments. In basalt, gabbro, serpentinite. In volcanic altered rocks
Altered to clay, zeolites.
CHALCEDONY
SiO2
(Oxide, Quartz group, a fibrous quartz variety)
Colorless, pale brown
Cloudy, nearly opaque due to inclusions. Zoning.
Spherulitic, fibrousNone.
Feactures parallel to the fibers
 Length fastΔn=0.005-0.009
1st order
L(-) L(+)
no=1.53-1.544
ne=1.53-1.553
U(+)
Hexagonal Trigonal
Almost impossible to obtain.
 Sedimentary. Volcanic. Hydrothermal.
CHLORITE
(Mg,Al,Fe)3(Si,Al)4O10(OH)2.(Mg,Al,Fe)3(OH)6
(Phyllosilicate of the chlorite series: Clinochlore (Mg), Chamosite (Fe) Pennantite (Mn), etc.)
photo photo photo
Green. Darker when more Fe.
Pl. (for B+): X=Y= green, pale green, brownish green, Z= colorless, pale green, pale yellowish green
Pl. (for B-): X= colorless, pale green, pale yellow green, Y=Z= pale green, green, olive green
Plates, scales, hexagonal xls{001} perfectTwin on (001) difficult to recognizeExt. // to inclined ~ <9°
Length fast B(+)
Length slow B(-)
Δn=0.0-0.02
Often low, to 1st order white or yellow
Anomalous yellow-brown, olive brown, indgo-violet
L(+) M(+) H(+)
nx=1.57-1.67
ny=1.57-1.69
nz=1.57-1.69
B(+) or B(-)
Monoclinic and Triclinic
2Vz=0°-60° (+)
2Vx=0°-40° (-)
Metamorphic. With biotite, garnet, staurolite, muscovite, andalusite, chloritoid, cordierite.
Mafic. With talc serpentine, actinolite, hornblende, epidote, garnet, chloritoid.
From hydrothermal alteration of biotite, amphibole, pyroxene
CHLORITOID
(Fe++,Mg,Mn)2Al4Si2O10(OH)4
(Nesosilicate)
camera
Green, brown, colorless.
Color zoning, hourglass.
Pl. X= green, grey green, Y= blue grey, reddish blue, blue green, Z= colorless, yellow, pale green
Platy, rectangular xls; hexagonal section, prismatic.
Inclusions (quartz,etc.)
// {001} perfect
2 poor cleavages on {110}
Simple or lamellar on {001}Inclined ext. 0°-18°
Length fast
Δn=0.005-0.022 (often 0.010-0.012). Up to pale 1st order yellow. Varieties to lower 2nd order.H(+)
nx=1.705-1.730
ny=1.708-1.734
nz=1.712-1.740
B(+) Monoclinic
B(-) Triclinic
2Vz=36°-72° (monoclinic)
2Vx=55°-88° (triclinic)
r>v strong
Metamorphic: phyllite, quartzite, schist. In emery deposits.
With garnet, staurolite, chlorite, muscovite.
Altered to chlorite, sericite, clay
CHONDRODITE
(Mg,Fe++)5(SiO4)2(F,OH)2
(Nesosilicate, humite group)
Colorless, pale yellow, yellow, orangish yellow. Darker color when Fe, Ti increase
Weak Pl. X= colorless, very pale yellow, brownish yellow, Y= colorless, yellowish green, Z= colorless, pale green
Grains. Platy xls{100}Simple or multiple twinsExt. in (010): 22° - 31°
Length fast or length slow
Δn=0.028-0.034
2nd order
M(+) H(+)
nx=1.592-1.617
ny=1.602-1.635
nz=1.621-1.646
B(+)
Monoclinic
2Vz=50°-85°
r>v
In contact metamorphic limestone and dolomite. In skarns. With tremolite, wollastonite, grossular, monticellite, forsterite, calcite, dolomite
In mafic igneous rocks
Altered to serpentine, chlorite
CLINOHUMITE
(Mg,Fe++)9(SiO4)4(F,OH)2
(Nesosilicate, humite group)
Colorless, pale yellow, yellow, orangish yellow. Darker color when Fe, Ti increase
Weak Pl. X= golden yellow, deep reddish yellow, Y= pale yellow, orange yellow, pale yellowish red, Z= pale yellow, orange yellow, colorless
Grains. Platy xls{100}Simple or multiple twinsExt. in (010): 9°-15°
Length fast or length slow
Δn=0.028-0.041
Bright upper 2nd order
M(+) H(+)
nx=1.628-1.638
ny=1.641-1.654
nz=1.662-1.674
B(+)
Monoclinic
2Vz=73°-76°
r>v
In contact metamorphic limestone and dolomite. In skarns. With tremolite, wollastonite, grossular, monticellite, forsterite, calcite, dolomite
In mafic igneous rocks
Altered to serpentine, chlorite
CLINOPYROXENE
(Inosilicate. A series in the Pyroxene supergroup: Augite, Clinoenstatite, Diopside, Esseneite, Hedenbergite, Jadeite, Johannsenite, Omphacite, Pigeonite, Spodumene, etc.)
Fe,Mg cpx: Clinoenstatite, Pigeonite, Clinoferrosilite
Ca cpx: Diopside, Hedenbergite, Augite
Na,Ca cpx: Omphacite, Aegirine-Augite
Na cpx: Jadeite, Aegirine
Li cpx: Spodumene
Usually colorless, grey, pale green or pale brown, darker colors associated with Fe-rich varieties
Titanaugite is more distinctly colored from brown/pink to violet.
Stubby prismatic elongated along the c-axis. Equant xls shapes: basal sections are 4 or 8 sided and show two cleavages at ~90°Typical pyroxene cleavages parallel to {110}, which intersect at ~90° (87°-93°)Simple and lamellar twins and composition planes, which in combination may form a herringbone patternInclined extinction. Sections // to (010) show max. Birefringence, a single cleavage and z^c of 35 to 48°Δn=0.018-0.034
Lower to middle 2nd order
H(+)
nx=1.664-1.745
ny=1.672-1.753
nz=1.694-1.771
B(+) B(-) Often positive
Monoclinic
2V=25°-70°Common in mafic igneous rocks, alkali-rich varieties may be found in more silicic rocks, often associated with olivine, orthopyroxene, and plagioclase.
Commonly altered to uralite (a  light colored amphibole), or may alter to serpentine, chlorite, biotite, carbonates and/or other silicates.
(Distinguishing features: Inclined extinction, higher birefringence, 2nd order interference colors, low 2V, optically positive in comparison with orthopyroxene Olivine lacks cleavage and has higher birefringence)
CLINOZOISITE
Ca2Al3[Si2O7][SiO4]O(OH)
(Sorosilicate. Clinozoisite - Epidote series)
camera
Colorless.

XPL: anomalous blue. interference colors unevenly distributed. No Pl.
Prismatic, columnar, bladed. Radiated. Sections rectangular or 6 sided.{001 perfect}Lamellar {100}Inclined ext. 0°-30°; up to 60°
Length slow
Δn=0.004-0.015Lower to middle 1st order (also anomalously bluish or greenish yellow)H(+)
nx=1.703-1.715
ny=1.707-1.725
nz=1.709-1.734
B(+); also B(-)
Monoclinic
2Vz=14°-100°
r<v clinozoisite
Green schists. Blue schists. In quartzite, slate, phyllite, chlorite schist, mica schist, gneiss, skarn, hornfels.
CORDIERITE
Mg2Al4Si5O18
(Cyclosilicate)
photo
Colorless. Also light blue
Pl. X= colorless, pale yellow, pale green, Y= pale blue, violet, Z= pale blue
Grains. Hexagonal prismatic.{010}Lamellar and cyclic twinning {110}, {130}Inclined ext. from // to 30° or 60°Δn=0.008-0.018
1st order grey to white
L(-) L(+)
nx=1.527-1.560
ny=1.532-1.574
nz=1.537-1.578
B(-) or B(+)
Orthorhombic (pseudohexagonal)
2Vx=35°-90° (-)
2Vz=74°-90° (+)
r<v weak; also r>v
In metapelites with chlorite, kyanite, andalusite, sillimanite, staurolite, muscovite, biotite, chloritoid
In metamorphic with anthophyllite, garnet
Altered to pinite, a mixture of mica and clay minerals.
CORUNDUM
Al2O3
(Oxide)
photo
Colorless, pale blue, red. Irregular patches. Hexagonal zones.
Weak Pl. o>e o= blue, purple, e= blue, blue green, yellowish green, yellow
Hexagonal prismatic. Hexagonal, rectangular sections.Tabular.
Inclusions are common.
Basal parting {0001, rhombohedral planes parting {10-11}Multiple lamellar on {10-11}. Contact twin {10-11} or {0001}// extinction
// to basal parting
Symmetrical to rhombohedral parting planes
Length fast
Δn='.007-0.010
1st order grey, white, to pale yellow
H(+)
no=1.767-1.772
ne=1.759-1.763
U(-) Also anomalous B(-)
Trigonal
Also anomalous B(-) with 2Vx up to 58°In Al-rich, Si-poor environment. Plutonic igneous, syenite, nepheline syenite, monzonite. In quartz-free pegmatite. Volcanic, in andesite dykes. Metamorphic, mica schist, chlorite schist. In contact zones between igneous rocks and limestone: emery deposits.
With spinel, cordierite. sillimanite, garnet, tourmaline, kyanite, rutile, magnetite, ilmenite
CRISTOBALITE
SiO2
(Oxide, Quartz group)
ColorlessOctahedron, cubicNone{111} Δn=0.003M(-)
no=1.487
ne=1.484
U(-)
Tetragonal (pseudoisometric)
 Volcanic. Shallow plutonic. With tridymite, topaz, garnet, fayalite.
In serpentinites: lussatite
Replaced by quartz
CROSSITE
Na2(Mg,Fe++)3(Al,Fe+++)2Si8O22(OH)2
(Inosilicate, clinoamphibole. Intermediate in the Glaucophane - Riebeckite series:
Colorless to blue
Pl. X= colorless, pale blue, yellow, Y= lavender blue, bluish green, Z= blue, greenish blue, violet
Prismatic columnar, bladed, acicular, fibrous{110} intersects at ~ 55° and 125°Simple or lamellar on {100}Inclined ext. less than ~22°. Usually less than 10°
Length slow or fast
Δn=0.012-0.016
Middle to upper 1st order
M(+) H(+)
nx=1.647-1.690
ny=1.663-1.690
nz=1.663-1.702
B(+) or B(-)
Monoclinic
2Vx=0°-180°
r>v or r<v very strong
Blue schists: metamorphic high -pressure low temperature
With lawsonite, garnet, pumpellyite, chlorite, albite, quartz, epidote.
Also in eclogites with garnet, hornblende, omphacite.
CUMMINGTONITE
[]Mg7Si8O22(OH)2
(Inosilicate, clinoamphibole: Cummingtonite - Grunerite series)
Colorless, pale green, brown. Color increases with higher Fe content.
Weak pleochroism (colored sections) X= colorless, pale yellow, Y=pale yellow, pale brown, Z=pale green, pale brown
Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section{110} intersects at 56° and 124°. Cummingtonite: Inclined ext. 15°-21° (010)
Length slow.
Δn=0.022-0.035
Up to 2nd order.
Δn increases with increasing Fe content.
M(+) H(+)
nx=1.632-1.663
ny=1.638-1.677
nz=1.655-1.697
R.I. increases with increasing Fe content.
B (+)
Monoclinic
B(+): >30-40% Mg, 2Vz=68°-90°
B(-): <30-40% Mg, 2V=83°-90°
2Vz=70°-90°
Weak, r<v
Mafic. Metamorphic, amphibolites, gneiss, hornfels, granulite, Diorite. Rare Intermediate volcanics
With anthophyllite, gedrite, garnet, cordierite, plagioclase, hornblende, biotite
Altered to hornblende, talc, serpentine
CUPRITE
Cu2O
(Oxide)
Red, orange, yellow. No Pl.Octahedral, cubic, dodecahedral{111} fair   VH(+)
n=2.849
Isotropic
Cubic
 In oxidized zone of hydrothermal Cu deposits
With malachite, azurite, copper
Altered to malachite, copper
DATOLITE
CaB(SiO4)OH
(Nesosilicate)
ColorlessMassive formNoneNoneNo consistent elongation shownΔn=0.044-0.046
Btight 1st order, 2nd order, to middle 3rd order
H(+)
nx=1.622-1.626
ny=1.649-1.654
nz=1.666-1.670
B(-)
Monoclinic
2Vx=72°-75°
r>v weak
Cavities in basalt, andesite, diabase, with zeolites, prehnite, calcite, danburite.
In contact metamorphic marbles or skarns, with calcite, prehnite, aegirine-augite, fluorite.
Rare in granite, serpentinite, basic schists and hydrothermal veins
DIOPSIDE
CaMgSi2O6
(Inosilicate, calcic clinopyroxene. Diopside - Hedenbergite series)
(Di100-Di50)
Colorless, grey, pale green, pale brown, brownish green.
Weak Pl pale green, greenish brown, bluish green, yellow green.
Stubby prismatic xls{110} distinct, intersect at ~87°. Parting {001} and {100}{100} or {001} lamellar, possible herringbone patternBasal (2 cleavages) symmetrical ext.
// c: inclined 35°-48°
// (100) is length slow
Δn=0.030
2nd order
H(+)
nx=1.664-1.672
ny=1.672-1.681
nz=1.694-1.702
R.I. increases with Fe content
B(+)
Monoclinic
2Vz=57°-58° increase with Ca content
r>v weak
In calc-silicates marble, skarn, pyroxene granulites.Alkali-olivine basalt and alkali igneous rocks. Cr diopside in ultramafic (kimberlite, peridotite). Metamorphic in Ca-Mg sediments.
Altered to uralite, talc, serpentine, chlorite
DOLOMITE
CaMg(CO3)2
(Carbonate. Dolomite group)
ColorlessRhombohedrons, curved faces{10-11} perfect
Some deformation twins (if present) bisect obtuse cleavage angle (see calcite)
{02-21} lamellar
Simple: {0001}, {10-10}, {11-20}, {10-11}
Symmetrical or inclinedΔn=0.179-0.185
High upper order white or grey
M(-) M(+) H(+)
no=1.679-1.703
ne=1.500-1520
U(-)
Hexagonal, Trigonal
 In limestone, dolomite. In evaporites.
Metamorphic: marble. With calcite, talc, forsterite, tremolite, actinolite, wollastonite. Hydrothermal
DUMORTIERITE
Al7(BO3)(SiO4)3O3
(Nesosilicate)
photo
Blue. Pl. X=cobalt blue, violet, red green, brown, Y=colorless, yellow, lilac, green, pale blue or green, Z=colorless, yellow, light blue, light greenBladed, acicular, prismatic, elongated{100} good, {110} poorCyclic {110}: show ~ hexagonal cross sectionExt.//
Length fast
Δn=0.011-0.037
1st order yellow; up to 2nd order
Increase with Fe
H(+)
nx=1.659-1.686
ny=1.684-1.722
nz=1.686-1.723
B(-)
Orthorhombic, pseudohexagonal
2Vx=13°-55°Granitic pegmatite, aplite. Hydrothermal
Medium and high grade metamorphic gneiss, quartzite, pelitic schist. With kyanite, sillimanite, cordierite, andalusite
Altered to white mica.
ECKERMANNITE
NaNa2(Mg4Al)Si8O22(OH)2
(Inosilicate, clinoamphibole. Series arfvedsonite - eckermannite)
(FERROECKERMANNITE = NaNa2(Fe++Al)Si8O22(OH)2)
Blue green, brown, violet
Pl. X= blue green, Y= pale blue green, Z= pale yellowish green
Bladed, prismatic, fibrous. Rhombic basal section.{110} intersects at 56° and 124°.
Simple or lamellar on {100}Symmetrical (basal).
// (100). Inclined on other longitudinal sections
Length fast.
Δn=0.01-0.02. Up to 1st order redM(+)
nx=1.61-1.64
ny=1.62-1.65
nz=1.63-1.66
B(-)
Monoclinic
2Vx=15°-80°In alkaline igneous rocks: granite, syenite, trachyte, phonolite, pegmatite. With aegirine, aegirine-augite, biotite, feldspar, nepheline.
Altered to uralite, iron oxides, carbonates.
ENSTATITE (En100-En88)
Mg2Si2O6
(Inosilicate, orthopyroxene. Enstatite - Ferrosilite series)
Colorless. Pale colored.
No or weak Pl.
Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages.
Exsolution lamellae (augite)
Good // {210}, intersect at ~ 88°.
Parting on {100}, {010} and {001} with exsolution lamellae (augite)
Fine lamellar // {100} is often exsolution lamellaeExt. //.
Basal: symmetrical
Cleavage trace length slow.
Δn=0.008-0.011
Up to 1st order yellow
M(+) H(+)
En100:
nx=1.654
ny=1.655
nz=1.665
B(+)
Orthorhombic
2Vz=35°-90°
r>v weak
In gabbro, pyroxenites, peridotites, dunites, serpentinites.
With olivine, Mg-rich clinopyroxenes phlogopite, plagioclase.
Altered to serpentine, amphibole, magnesite, talc
EPIDOTE
Ca2Al2Fe+++[Si2O7][SiO4]O(OH)
(Sorosilicate. Clinozoisite - Epidote series)
(There is also Epidote-Pb and Epidote-Sr)
cameraphoto
Light yellow green. Pleochroism colorless to yellow. Bright interference colors unevenly distributed. Piemontite: pink
Pl. X= colorless, pale yellow, pale green, Y= greenish yellow, Z= pale yellowish green
Prismatic, columnar, bladed, acicular. Radiated, sheaf aggregates. Sections rectangular or 6 sided.{001} perfect, {100} poorLamellar {100}Inclined ext. 20°-40° Z/\x
Length slow
Δn=0.015-0.051
1st order, 2nd order, Also 3rd order bluish or yellowish.
Concentrically zoned
H(+)
nx=1.715-1.751
ny=1.725-1.784
nz=1.794-1.797
B(-); also B(+)
Monoclinic
2Vx=64°-95°
r>v strong
Metamorphic green schists. Blue schists. In quartzite, slate, phyllite, chlorite schist, mica schist, gneiss, skarn, hornfels. In igneous rocks. Hydrothermal.
Plagioclase, biotite, hornblende, clinopyroxene may be altered to epidote.
EULITE (En30-En12)
(Fe++,Mg)2Si2O6
(Inosilicate, orthopyroxene. Enstatite - Ferrosilite series)
(A variety of Ferrosilite)
Colorless, pale colored.
Pl. X= brown, Y= yellow, yellow, Z= blue green
Stubby prismatic. Basal sections 6 or 8 sides, showing cleavagesGood // {210}, intersect at ~ 88°.
Parting on {100}, {010} and {001}
{101}Ext. //.
Basal: symmetrical
Cleavage trace length slow
Δn=0.018-0.020
Up to lower 2nd order
H(+)
nx=1.734-1.755
ny=1.747-1.765
nz=1.752-1.775
B(+)
Orthorhombic
2Vz=62°-90°
v>r moderate
In metamorphosed Fe sediments with Fe-olivine, diorites, monzonites.
Altered to bastite, uralite.
FAYALITE
Fe++2SiO4
(Nesosilicate. Fo0-Fo50 olivine forsterite - fayalite series)
Colorless to pale yellow, red brown.
PL. X=Z= pale yellow, Y= orange brown, yellowish brown, reddish brown
Bipyramidal, stubby prismatic{010} distinct
{110} poor, usually not seen
{100}, {011}, {012}: simple
{031} cyclic
Ext. // (elongated xls)
Length fast or length slow
Δn=0.052
3rd order
H(+)
nx=1.734-1.827
ny=1.760-1.869
nz=1.778-1.879
R.I. increases from Fo100 to Fo0
B(-)
Orthorhombic
2Vx=46°-72°
r>v weak
2Vx decreases from Fo100 to Fo0
Fe rich: plutonic, volcanic. In syenite, nepheline syenite, phonolite, trachyte, andesite, dacite.
Mg Fe: plutonic, volcanic, mafic, ultramafic. In gabbro, pyroxenite, peridotite, dunite
Mn rich: In Fe Mn deposits, skarns
Altered to serpentines, iddingsites.
FERRO-ACTINOLITE
[]Ca2Fe++5Si8O22(OH)2
(Inosilicate. Clinoamphibole, Tremolite - Actinolite - Ferro-actinolite series.).
photo
Dark green to black. Color increases with Fe content.
Pl. X=colorless, pale yellow green, Y=pale yellow green, pale blue green, green Z= pale green, green, blue-green, dark green
Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section.{110} intersects at 56° and 124°. Visible on basal sectionsSimple or {100} lamellar, // to the long diagonal of basal section.Inclined 12°-18°.
Sections // to (100) show // extinction
Length slow.
Δn=0.018-0.019
Upper 1st order to mid 2nd order
H(+)
nx=1.669-1.686
ny=1.680-1.696
nz=1.688-1.704
R.I. increases with increasing Fe content.
B(-)
Monoclinic
2Vx=63°-75°
r<v weak
Metamorphic rocks and regional contact metamorphic.
Altered to chlorite, talc, amphibole.
FERROHYPERSTHENE (En50-En30)
(Fe++,Mg)2Si2O6
(Inosilicate, orthopyroxene. Enstatite - Ferrosilite series)
(A variety of Ferrosilite)
Pale colored, pinkish to greenish.
Pl. X= salmon pink, Y= yellow, Z= blue green
Stubby prismatic. Basal sections 6 or 8 sides,{110} distinct
intersect at ~87°.
Parting on {010} and {001}.
{101}Ext. //.
Basal: symmetrical
Cleavage trace length slow
Δn=0.015-0.018
1st order
H(+)
nx=1.710-1.734
ny=1.722-1.747
nz=1.725-1.752
B(+)
Orthorhombic
2Vz=53°-62°
v>r weak
In gabbro, diorite, monzonite. In metamorphosed Fe-sediments
Altered to bastite, uralite (fibrous actinolite-tremolite)
FERROSILITE (En12-En0)
(Fe++,Mg)2Si2O6
(Inosilicate, orthopyroxene. Enstatite - Ferrosilite series)
Deep green to brown.
Pl.
Stubby prismatic. Basal sections 6 or 8 sides, showing cleavagesGood // {210}, intersect at ~ 88°.
Parting on {100}, {010} and {001} with exsolution lamellae (augite)
{101}Ext. //.
Basal: symmetrical
Cleavage trace length slow
Δn=0.015-0.022
Up to lower 2nd order
H(+)
nx=1.755-1.768
ny=1.765-1.771
nz=1.775-1.188
B(+)
Orthorhombic
2Vz=90°35°
r>v strong
Thermal metamorphism of Fe-rich rocks
FLUORITE
CaF2
(Halide)
photo
Colorless, bluish, purplish, pinkish, greenish.
No Pl.
Cubic, octahedral, dodecahedral.{111} perfect octahedralPenetration twins {111}  M(-)
n=1.433-1.435
Isotropic
Cubic
 Hydrothermal deposits, with sulfides. Granite, syenite, granitic pegmatite. In carbonate sediments. Cementing clastic sediments.
FORSTERITE
Mg2SiO4
(Nesosilicate. Fo100-Fo50, olivine forsterite - fayalite series)
Colorless to pale green
No Pl.
Bipyramidal, stubby prismatic{010}, {110}: poor{100}, {011}, {012}: simple
{031} cyclic
Ext. // (elongated xls)
Length fast or length slow
Δn=0.035 - 0043
2nd order
M(+) H(+)
nx=1.635-1.73
ny=1.651-1.76
nz=1.670-1.77
R.I. increases from Fo100 to Fo0
B(+)
Orthorhombic
Also B(-)
2Vx=72°-98°
v>r or r>v, weak
2V decreases from Fo100 to Fo0
Mg rich: with calcite, dolomite, diopside, epidote, grossular, tremolite
Mg Fe: plutonic, volcanic, mafic, ultramafic. In gabbro, pyroxenite, peridotite, dunite
Altered to serpentines, iddingsites.
GARNET group
(Nesosilicates. Garnet group)
Pyralspites:
Pyrope Mg3Al2(SiO4)3
Almandine Fe3Al2(SiO4)3
Spessartine Mn3Al2(SiO4)3
Ugrandites:
Grossular Ca3Al2(SiO4)3
Andradite Ca3Fe2(SiO4)3
Uvarovite Ca3Cr2(SiO4)3
Hydrogrossular Ca3Al2(SiO4)3-x(OH)4x
photo photo
Colorless, pale colored, reddish, pinkish, greenish, yellowish.
No Pl.
Dodecahedral {110}, trapezohedral {112}. 6 or 6 sided cross section.
Quartz inclusions
Parting // to dodecahedral {110} facesNo twinning  H(+)
n=1.72-1.77 Pyrope
n=1.77-1.82 Almandine
n=1.79-1.81 Spessartine
n=1.735-1.77 Grossular
n=1.85-1.89 Andradite
n=1.838-1.87 Uvarovite
n=1.675-1.734 Hydrogrossular
Isotropic
Cubic
 Metamorphic. Mica schists, gneiss, pegmatite, granite, felsic igneous: Almandine
Ultramafic igneous rocks, peridotites, serpentinites: Pyrope
Granite, pegmatite, felsic igneous: Spessartine
Skarn: Grossular. With calcite, dolomite, wollastonite, tremolite, epidote
Skarn, hydrothermal veins: Andradite
Cr igneous rocks, peridotite: Uvarovite
Altered to chlorite, actinolite,hornblende, epidote, iron oxides, biotite
GEDRITE
[](Mg,Fe++)5Al2Si6Al2O22(OH)2
(Inosilicate, orthoamphibole)
(There is also Ferrogedrite, Sodiumgedrite)
Pale brown, yellow-brown, greenish brown. Darker when Fe increases.
No or weak Pl. X=Y= pale yellowish, pale greenish, greyish brown, Z= yellowish brown, greenish grey, greyish brown, purplish brown.
Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section.{210} intersects at 55° and 125°. Symmetrical (basal).
// (longitudinal)
Length slow.
Δn=0.016-0.028
1st order red, 2nd order blue, green. Birefringence increasing with Fe content.
M(+) H(+)
nx=1.615-1.694
ny=1.625-1.710
nz=1.634-1.722
B(+) or B(-)
Orthorhombic
2Vz=57°-108°
Weak, r<v (+), r>v (-)
Medium and high grade metamorphic: amphibolite, gneiss, granulite, hornfels, talc schist. With garnet, cordierite, anthophyllite, hornblende, sillimanite, plagioclase.
Altered to serpentine, talc.
GLAUCONITE
(K,Na)(Mg,Fe++,Fe+++)(Fe+++,Al)(Si,Al)4O10(OH)2
(Phyllosilicate, mica group)
photo
Green. Al-rich glauconite: pale green, colorless
Distinct Pl. X= yellowish green, green, Y=Z= green, bluish green, darker yellowish green
Granules, micaceous, flakes{001} perfect often not visible since too fine grained // extinction to cleavage
Trace of cleavage: length slow
Δn=0.02-0.03
Upper 1st order, 2nd order
M(+)
nx=1.59-1.61
ny=1.61-1.64
nz=1.61-1.64
B(-)
Monoclinic
Basal sections almost isotropic
2Vx=0°-20°Granules in detritical sediments of marine origin "greensands".
Altered to limonite and goethite.
GLAUCOPHANE
[]Na2(Mg3Al2)Si8O22(OH)2
(Inosilicate, clinoamphibole. Glaucophane - Riebeckite series)
(There is also Ferroglaucophane)
camera
Colorless to blue, lavender blue, pale bluish green
Pl. X= colorless, pale blue, yellow, Y= lavender blue, bluish green, Z= blue, greenish blue, violet
Bladed, prismatic, fibrous (crocidolite). Rhombic basal section.2 cleavages {110} intersect at ~ 58° and ~122°Simple or lamellar on {100}, not common.Inclined ext. less than ~22°
According to Tröger: 5°-10°
Length slow.
Δn=0.008-0.029
Middle to upper 1st order and beginning 2nd order.
M(+)
nx=1.594-1.647
ny=1.612-1.663
nz=1.618-1.663
B (-)
Monoclinic
2Vx=10°-50°
r<v weak
Blue schists: metamorphic high pressure low temperature
With lawsonite, garnet, pumpellyite, chlorite, albite, quartz, epidote.
Also in eclogites with garnet, hornblende, omphacite, clinozoisite.
GRUNERITE
[]Fe++7Si8O22(OH)2
(Inosilicate, clinoamphibole. Cummingtonite - Grunerite series)
(There is also Manganogrunerite)
Colorless, pale green, brown. Color increases with higher Fe content.
Weak pleochroism (colored sections) X= colorless, pale yellow, Y=pale yellow, pale brown, Z=pale green, pale brown
Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section.{110} intersects at 56° and 124°.Simple and lamellar {100}Inclined 10°-20°
Length slow.
Δn=0.036-0.044
Up to mid 3rd order. Δn increases with increasing Fe content.
H(+)
nx=1.664-1.688
ny=1.682-1.712
nz=1.700-1.732
R.I. increases with increasing Fe content.
B (-)
Monoclinic
2Vz=80°-90°
Weak, r>v
Metamorphic.
With magnetite, quartz.
Altered to hornblende, talc, serpentine
GYPSUM
CaSO4.2H2O
(Sulfate)
Colorless
Zoning
Tabular, prismatic, acicular{010} perfect, {100} good, {111} good Intersect at 42° and 138°Simple contact twins {100} (butterfly twins)Maximum inclined ext. angle seen on {010}: ~38° to {100} cleavageΔn=0.010 weak 1st order grey, white, pale yellowL(-)
nx=1.519-1.521
ny=1.522-1.526
nz=1.529-1.531
B(+)
Monoclinic
2Vz=58°In evaporites, with halite, sylvite, anhydrite, calcite, dolomite, clay. Anhydrite hydrates to become gypsum
Pseudomorphs after anhydrite, calcite, halite. Replaced by chalcedony, opal, calcite, aragonite, anhydrite, celestite.
HAUYNE
(Na,Ca,K)8-4(SO4)2-1(AlSiO4)6
(Hauÿne. Tectosilicate, feldspathoid, sodalite group)
photo photo
Blue, colorless. Irregularly colored. Dark rim: "Trauerrand".
No Pl.
Dodecahedral, six sided cross section{110} poor dodecahedral{111} seldom  M(-)
n=1.494-1.509
Isotropic
Cubic
 In Si-deficient volcanic: phonolite, alkaline basalt, feldspathoid basalt, trachyte. Plutonic.
With nepheline, leucite, sanidine.
Altered to zeolite (fibrous), clay, calcite, cancrinite.
HEDENBERGITE
CaFe++Si2O6
(Inosilicate, calcic clinopyroxene. Diopside - Hedenbergite series)
(Di50- Di0)
Colorless, grey, pale green, pale brown, brownish green. No or Weak Pl pale green, greenish brown, bluish green, yellow green.Prismatic, radiated columnar, acicular xls{110} distinct, intersect at ~87°. Parting {001} and {100}{100} or {001} lamellar, possible herringbone pattern (rare)Basal (2 cleavages) symmetrical ext.
// c: inclined 35°-48°
// (100) is length slow
Δn=0.028-0.029
Up to second order.
H(+)
nx=1.722-1.728
ny=1.730-1.736
nz=1.750-1.757
R.I. increases with Fe content
B(+)
Monoclinic
2Vz=62°-63° increase with Ca content
r>v strong
Skarns and siliceous hornfels with grunerite. Alkali granites.
HEMATITE
Fe2O3
(Oxide)
Opaque mineral. Deep brown red on very thin xls or edges.
Pl. o=brownish red, e=yellowish red or brown, o>e
Tabular, hexagonal, fibrous, botryoidal, scaly, etc.Basal parting {001}, rhombohedral parting {101}NoneExt // to basal partingΔn=0.28
High upper order
VH(+)
no=3.15-3.22
ne=2.87-2.94
U(-)
Hexagonal, Trigonal
 Common Fe-oxide in all rock types.
HEULANDITE
(Ca0,5,Na,K)9[Al9Si27O72].24H2O
(Tectosilicate, zeolite, heulandite - stilbite - brewsterite group)
)There is Heulandite-Ba, -Ca, -K, -Na, -Sr)
ColorlessTabular // (010), trapezohedral outline{010} perfect ~// extinction to the trace of cleavage
Sections cut // {010} show inclined ext. to xl outlines (no cleavage)
Length fast on cleavage trace
Δn=0.006-0.009M(-) L(-)
nx=1.492-1.505
ny=1.494-1.506
nz=1.501-1.512
B(+)
Monoclinic
2Vz= ~ 30° (=°-50°)
r>v
In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks.
HORNBLENDE
[]Ca2[Fe++4(Al,Fe+++)]Si7AlO22(OH)2
(Inosilicate, clinoamphibole, a series name)
(There is Ferrohornblende, Magnesiohornblende)
Green, yellow-green, blue-green, brown
Pl. green hornblende: X= light yellow, light yellow green, light blue green, Y= green, yellow green, grey green, Z= dark green, dark blue green, dark grey green
Pl. brownish hornblende: X= yellow, greenish yellow, light greenish brown, Y= yellow brown, brown, reddish brown, Z= grey brown, dark brown, reddish brown
Prismatic, bladed. Rhombic basal section.2 cleavages {110} intersect at 56° and 124°.Simple and lamellar on {100}Symmetrical (basal).
Sections // (010): inclined 12°-34° (often 14°-25°)
Length slow
Δn=0.014-0.034 (often 0.018-0.028)
Upper 1st order to lower 2nd order
M(+) H(+)
nx=1.60-1.70
ny=1.61-1.71
nz=1.62-1.73
B(+) or B(-)
Monoclinic
2Vx=35°-130° (often about 75°)
Ubiquitous. Igneous plutonic, volcanic, mafic, metamorphic: diorite, andesite, rhyolite, gabbro. Metamorphic: amphibolite, marble, skarn
Altered to uralite, chlorite, biotite
HUMITE
(Mg,Fe++)7(SiO4)3(F,OH)2
(Nesosilicate, humite group)
Colorless, pale yellow, yellow, orangish yellow. Darker color when Fe, Ti increase
Weak Pl. X= very pale yellow, dark yellow, Y= colorless, pale yellow, Z= colorless, pale yellow
Grains. Platy xls{100}Simple or multiple twinsEither length fast or length slowΔn=0.029-0.036
Bright upper 2nd order
M(+) H(+)
nx=1.607-1.643
ny=1.619-1.655
nz=1.639-1.675
B(+)
Orthorhombic
2Vz=65°-84°
r>v
In contact metamorphic limestone and dolomite. In skarns. With tremolite, wollastonite, grossular, monticellite, forsterite, calcite, dolomite
In mafic igneous rocks
Altered to serpentine, chlorite
HYALOPHANE
(K,Ba)Al(Si,Al)3O8
(Tectosilicate. Ba feldspar)
ColorlessTabular, prismatic, elongated xls{001} perfect, {010} distinct, intersecting at 90°. {110} poorSimple, Carlsbad, Manebach, Baveno. No multiple twinning.Max.0°-19°° on {001} cleavageΔn=0.005-0.010
1st order grey, white or pale yellow
L(-) to L(+)
nx=1.520-1.542
ny=1.524-1.545
nz=1.526-1.547
B(-)
Monoclinic
2Vz=48°-79°
r>v
Hydrothermal veins in rich Mn rocks. Granite gneiss.
With Mn minerals, rhodonite, rhodochrosite, spessartine
HYPERSTHENE (En70-En50)
(Mg,Fe++)2Si2O6
(Inosilicate, orthopyroxene. Enstatite - Ferrosilite series)
Pale colored, pinkish to greenish.
Pl. X= pink, brownish pink, pale yellow, Y= light brown, yellow, pinkish yellow, greenish yellow, Z= light green, grey green, bluish green
Stubby prismatic. Basal sections 6 or 8 sides, showing cleavages
Exsolution lamellae (augite).
Good // {210}, intersect at ~ 88°. Exsolution lamellae (augite)
Parting on {010} and {001}.
Fine exsolution exsolution lamellae // (100)Ext. //.
Basal: symmetrical
Cleavage trace length slow
Δn=0.008-0.020
1st order
H(+)
nx=1.699
ny=1.711
nz=1.714
B(+)
Orthorhombic
2Vz=50°-57°Plutonic and volcanic.
In norite, gabbro.
Ferrohypersthene in diorite, monzonite, granite. xls of orthopyroxene surrounded by a rim of clinopyroxene.
ILLITE
K0,65Al2[]Al0,65Si3,35O10(OH)2
(Phyllosilicate, hydromica group; a clay mineral)
photo
ColorlessFine crystalline.{001} perfect, normally not visible Extinction ~ //
Length slow
Δn=0.020L(+) M(+)
nx=1.53-1.57
ny=1.56-1.61
nz=1.56-1.61
B(-)
Monoclinic
2Vx<10°, often not possible to determine.Common in diagenetic to low-grade sedimentary rocks. In alkali granites. In ore veins.
It alters K-feldspar, muscovite, kaolinite.
JADEITE
Na(Al,Fe+++)Si2O6
(Inosilicate, sodic clinopyroxene)
Colorless
Pl. pale green, yellow
Stubby prismatic. Acicular. Basal sections 4 or 8 sides{110} intersect at ~87°Simple or lamellar {100} or {001}Basal (2 cleavages) symmetrical ext.
Longitudinal // (100)
Inclined 32°-55° in (010) sections
Length slow
Δn=0.006-0.021, often 0.012-0.018
1st order yellow or red, also 2nd order
M(+) H(+)
nx=1.640-1.681
ny=1.645-1.684
nz=1.652-1.692
B(+) or B(-)
Monoclinic
2Vz=60°-96°, often ~70°
r>v weak to very strong
In high pressure metamorphic rocks: glaucophane schist, serpentinite.
With albite, glaucophane, actinolite,lawsonite, quartz, chlorite, garnet, zoisite, mica, calcite, aragonite,
Altered to amphibole
JOHANNSENITE
CaMn++Si2O6
(Inosilicate, clinopyroxene)
photo
ColorlessStubby prismatic, radiated acicular.{110} distinc
tParting on {100} or {001}.
Simple or lamellar {100} Δn=0.029nx=1.703-1716
ny=1.711-1.716
nz=1.732-1.745

B(+)
Monoclinic

2V=68°-73°
r>v moderate
Limestone contact zones with rhodonite. In rhyolite.
Alterates to rhodonite, xonotlite
KAERSUTITE
NaCa2(Mg4Ti)Si6Al2O23(OH)
(Inosilicate, clinoamphibole)
(There is also Ferrokaersutite)
Yellowish, reddish, greenish brown, fox brown.
Strong Pl. X= yellow, brownish yellow, Y= reddish brown, Z= dark reddish brown, greenish brown
Prismatic, bladed. Rhombic basal section. Often Color zoned{110} intersects at 56° and 124°.Simple or lamellar on {100}Symmetrical (basal).
Inclined 0°-19°
Length slow
Δn=0.02-0.08. 2nd order to 4th order, 5th order. Birefringence increasing with Fe content.H(+)
nx=1.67-1.71
ny=1.69-1.74
nz=1.70-1.77
B(-)
Monoclinic
2Vx=66°-82°
r>v strong
Alkaline rocks. Volcanic: trachyte. Intrusive: monzonite, syenite
With titanite, Ti augite, Ti biotite, Fe Ti oxides
Alteration: amphiboles, Ti augite, chlorite, Fe Ti oxides
KAOLINITE
Al2Si2O5(OH)4
(Phyllosilicate clay mineral group)
Colorless, greyish, brownish, ~ opaque
Pl. weak.
Often cloudy aggregate mass{001} perfect, normally not visible. Ext. //
Occasional slight inclined on (010)
Δn=0.005-0.008
1st order low grey
Montmorillonite clays show higher Δn than kaolinite clays.
L(+)
nx=1.553-1.565
ny=1.559-1.569
nz=1.560-1.570
B(-) Difficult to obtain figures
Triclinic (Kaolinite-1A)
Monoclinic (Kaolinite-1M)
Often almost isotropic
2Vx=23°-60°
r>v weak
Often not possible to determine
Altered to feldspars and Al-minerals, diaspore, gibbsite.
KYANITE
Al2SiO5
(Disthen. Nesosilicate sillimanite - andalusite - kyanite group)
photo
Colorless, light blue, pale greyish pinkish brown
Pl. weak X= colorless, Y=light violet blue, Z=light cobalt blue
Prismatic, elongated on c, Bladed xls, bent xls{100} perfect. {010} good, intersect at 74°
Basal parting {001} ~ right angle to xl length.
Simple or multiple on {100}. Multiple on {001}Inclined ext. max. 30°
7° on section // (010)
3° on basal section
Length slow
Δn=0.012-0.016
1st order yellow.
H(+)
nx=1.710-1.718
ny=1.719-1.725
nz=1.724-1.734
B(-)
Triclinic
2Vx=78°-84°
r>v weak
Metamorphic, mica schist, gneiss. Rarely in granitic pegmatite, eclogite, kimberlite.
With staurolite, sillimanite, andalusite, chloritoid, garnet
Altered to chlorite, margarite, pyrophyllite
LABRADORITE
(Ca,Na)[Al(Al,Si)Si2O8]
(Tectosilicate. plagioclase, An50-An70)
Colorless, clouded (alteration)Tabular, // to (010), prismatic, elongated. Common chemical zoning{001} perfect, {010} good, {110} poorAlbite polysynthetic. Pericline polysynthetic. Carlsbad penetrationInclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.008. Low: 1st order up to white
Optic related to anorthite content
L(+)
nx=1.560
ny=1.564
nz=1.568
B(+)
Triclinic
2Vx=80°
r>v weak
In gabbro, anorthosite, mafic rocks. Volcanic: basalt
Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite
LAUMONTITE
Ca4[Al8Si16O48].18H2O
(Tectosilicate, zeolite, laumontite - yugarawalite group)
photo
ColorlessPrismatic, fibrous{010} and {110} intersect// {100}Ext. 8°-33° in sections cut // (010)
Length slow
Basal sections: ext. // to {010} cleavage and symmetrical to {110} cleavage
Δn=0.010-0.012
1st order white
L(-)
nx=1.502-1.514
ny=1.512-1.522
nz=1.514-1.525
B(-)
Monoclinic
2Vx=26°-47°
r<v
In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks. Low grade metamorphic rocks.
Altered to zeolites.
LAWSONITE
CaAl2Si2O7(OH)2.H2O
(Sorosilicate, lawsonite group)
photo
Usually colorless.
Pl. X=light blue, brownish yellow, Y=yellow, yellow green, blue green, Z=colorless, light yellow
Tabular, rhombic, rectangular, prismatic, acicular2 perfect cleav. {010} and {100} intersect at right angles. 2 imperfect // {101} intersect ~ 67°Lamellar // {101}// extinctionΔn=0.019-0.021
1st order, beginning 2nd order
M(+) H(+)
nx=1.663-1.665
ny=1.672-1.675
nz=1.682-1.686
B(+)
Orthorhombic
2Vz=76°-87°In glaucophane schists with pumpellyite, chlorite and albite.
LEPIDOLITE
K(Li,Al)3(Si,Al)4O10(F,OH)2
(Phyllosilicate, Li-mica, mica group)
Colorless, pale pink, pale green
Pl. pink, violet, green shades
Tabular // (001), hexagonal outline, flakes{001} perfect ~ // to cleavage, inclined 0°-7°
Length slow
Δn=0.018-0.038
2nd order
(muscovite: ~ higher birefringence)
L(+) M(+)
(Muscovite: greater relief)
nx=1.525-1.548
ny=1.548-1.585
nz=1.554-1.587
B(-)
Monoclinic
2Vx=0°-58° (often 30°-50°)
r>v
In granitic pegmatites with quartz, K-feldspar, albite, beryl, tourmaline, spodumene
May be replaced by muscovite
LEUCITE
K[AlSi2O6]
(Tectosilicate. Feldspathoid)
photo
Colorless. Clouded.Trapezohedral xls, 8 sided section.
Oriented inclusions "Schlackenkränzchen"
{110} very poor, pseudododecahedralThin lamellar twins // {110}, arranged ~ concentricallyNo elongation.Δn=0.000-0.001
Lower 1st order grey.
L(-)
no=1.508-1.511
ne=1.509-1.511
U(+)
Tetragonal (pseudocubic, almost isotropic)
 Si-deficient volcanic: leucophonolite, leucotephrite, leucitite.
With olivine, nepheline, sanidine, clinopyroxene, phlogopite, apatite, Na Ca amphiboles.
Altered to pseudoleucite, a mixture.
MALACHITE
Cu2(CO3)(OH)2
(Carbonate)
Green
Pl. X=almost colorless, pale green, Y=yellowish green, Z=dark green
Concentric color banding, fibrous, botryoidalDifficult to see. {-201} perfect, {010} fair{100} common (difficult to see)Inclined ext. Length fast.Δn=0.254
High order(masked by mineral color)
M(+) H(+)
nx=1.655
ny=1.875
nz=1.909
B(-)
Monoclinic
2Vx=43°
r<v
In oxidized zone of hydrothermal Cu deposits
Altered to azurite, cuprite.
MAGNESITE
MgCO3
(Carbonate, calcite group)
Colorless. Cloudy.Rhombic, prismatic, lamellar, fibrousRhombohedral {10-11} perfectRare translation gliding on {0001}
No twin lamellae
Extinction symmetrical to basal cleavage traces or inclinedΔn=0.191
High order
L(-) L(+) M(+) H(+)
no=1.700
ne=1.509
U(-)
Hexagonal, Trigonal
 Alteration of Mg-rich rocks: serpentinite, peridotite, pyroxenite, dunite. Metamorphic. Sedimentary.
MELILITE group
(Ca,Na)2(Al,Mg)(Si,Al)2O7
(Sorosilicate. Includes Akermanite, Gehlenite, etc.)
Colorless, pale yellow
Weak pleochroism o>e o= golden brown e=pale yellow
Tabular // (001). Square, octagonal cross section. Rod inclusions // c{001} Ext. // in rectangular sections.
Length slow
Δn=0.001-0.013
Lower 1st order to mid 1st order; anomalous Berlin blue colors.
M(+) H(+)
no=1.624-1.666
ne=1.616-1.661
U(-) or U(+)
Tetragonal
Gehlenite U(-)
Akermanite U(+)
 In Si deficient mafic rocks. With Ca plagioclase, olivine, clinopyroxene, nepheline, leucite (in volcanic). Akermanite found in high-grade metamorphic carbonate rocks
With melanite (in plutonic). Not with quartz.
Altered to fibrous cebollite, zeolites, calcite.
MICROCLINE
KAlSi3O8
(Tectosilicate. K feldspar)
photo
Colorless. Brownish alteration.
Perthitic
Tabular and prismatic elongated xls.{001} perfect, {010} good, intersect at 91°Albite + pericline: cross-hatched twin pattern: "tartan plaid"
(anorthoclase is similar to microcline, but has ultra-fine twinning)
Inclined 15° on {001} cleavage. Inclined 5° on {010} cleavage.
Inclined 12° in cryptoperthites
Δn=0.005-0.008
Low: up to 1st order grey
L(-)
nx=1.514-1.516
ny=1.518-1.519
nz=1.521-1.522
B(-)
Triclinic
2Vx=~65°-88°Plutonic felsic igneous: granite, granodiorite, pegmatite, syenite. Metamorphic: gneiss. Authigenic in sedimentary rocks and hydrothermal veins: triclinic adularia with rhombic cross section.
Altered to sericite and clay.
MONTICELLITE
CaMgSiO4
(Nesosilicate, monticellite series)
ColorlessGrains, polygonal sections{010} poor{031} cyclic twinsElongate xls: length slow or long fastΔn=0.012-0.020
up to 1st order red
M(+) H(+)
nx=1.638-1.654
ny=1.646-1.664
nz=1.650-1.674
B(-)
Orthorhombic
2Vx=69°-88°
r>v
In contact metamorphic limestone and dolomite. In skarns. With calcite, dolomite, diopside, tremolite, forsterite, wollastonite.
In mafic igneous rocks
MONTMORILLONITE
(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2.nH2O
(Phyllosilicate. Clay mineral formerly smectite. Montmorillonite - vermiculite group)
Colorless, pale yellow, pinkish, brownish, ~ opaque
(Nontronite is bright green)
Flakes{001} perfectNot visibleExtinction ~ //
Length slow
Δn=0.01-0.04
Bright colors 2nd order.
Montmorillonite clays show higher Δn than kaolinite clays
M(-) L(-) L(+) M(+)
nx=1.48-1.57
ny=1.50-159
nz=1.50-1.60
B(-)
Monoclinic
2V=0° to 30°Alteration of igneous rocks in semiarid climates. Siliceous rocks tend to yield illite; mafic tend to yield montmorillonite.
Altered to kaolinite
MORDENITE
(Na2,Ca,K2)4(Al8Si40)O96.28H2O
(Tectosilicate, zeolite group)
photo
ColorlessRadiate, acicular fibrous{010} and {100} perfectNone Δn=0.002-0.005nx=1.472-1.483
ny=1.475-1.485
nz=1.477-1.487
B(-)
Orthorhombic
2V=76° to 90°Amygdules in volcanic rocks

MUSCOVITE
KAl2[]AlSi3O10(OH)2
(Phyllosilicate. Mica group.
Phengite: Si rich muscovite. Oellacherite Ba-rich. Fuchsite: Cr- rich. Alurgite: Mn-rich. Sericite: fine grained muscovite)
photo photo photo

Colorless. Rarely pale pink or green.Tabular {001}, bladed, hexagonal outline not often seen. Flakes striated with 1 perfect cleavage{001} perfect, seldom visibleRare on {001}Ext. // cleavage. Inclined ext. <3°.
Undulatory ext., Pebbly, birds-eye texture seen near extinction
Length slow // to cleavage.
Δn=0.035-0.049
high: up to upper 2nd order vivid colors, also 3rd order
L(+) M(+)
nx=1.552-1.576
ny=1.582-1.615
nz=1.587-1.618
B(-)
Monoclinic
2Vx=28°-47°
Phengite 2V=0°-20°
Paragonite 2V=0°-40°
(Colorless lepidolite and talc: smaller 2V. Colorless pyrophyllite: greater 2V)
r>v
Felsic plutonic. Granite, granodiorite, aplite, pegmatite.
Metamorphic, slate, schist, gneiss, hornfels, phyllite, quartzite
Phengite and paragonite in low grade metamorphic rocks.
Sericite: hydrothermal alteration of feldspars.

MYRMEKITE
A vermicular intergrowth of quartz in plagioclase
photo

         In metamorphic and granitic rocks
NATROLITE
Na2[Al2Si3O10].2H2O
(Tectosilicate, zeolite, natrolite group)
ColorlessPrismatic, acicular. Square cross section{110} perfect{110}, {001}, {031} RareExt. //. Basal section: symmetrical ext.
Length slow
Δn=0.012-0.013
White, grey, to 1st order yellow
M(-)
nx=1.473-1.483
ny=1.477-1.486
nz=1.485-1.496
B(+)
Orthorhombic (pseudotetragonal)
2Vz=58°-64°
r<v weak
In mafic low grade metamorphic and hydrothermal.
In altered volcanic rocks with other zeolites, analcime, stilbite, chabazite, heulandite, laumontite
NEPHELINE
(Na,K)AlSiO4
(Tectosilicate, feldspathoid)
photo
Colorless, cloudyStubby prismatic, rectangular. Square or hexagonal cross section.// {100}
// {001}
Usually not seen.
{100}, {112}, {335}, usually not seenExt. //Δn=0.003-0.006
1st order, low: up to dark grey
L(-)
nx=1.529-1.551
ny=1.526-1.547
U(-)
Hexagonal
 In silica undersaturated alkali magmatic rocks.
In volcanic rocks. With leucite, aegirine-augite, melanite, melilite, olivine, Ti-augite, Ti-biotite, apatite, cancrinite, feldspars.
Altered to sodalite, analcite, cancrinite, fibrous zeolite, sericite
NOSEAN
Na8Al6Si6O24(SO4).H2O
(Tectosilicate, feldspathoid, sodalite group)
photo photo
Colorless, grey, grey brown, very pale blue. Dark rim. No Pl.Six sided hexagonal cross sectionPoor {110}{111} seldom  M(-)
n=1.460-1.495
Isotropic
Cubic
 In silica deficient alcalic igneous rocks. Altered to zeolite (fibrous), clay, calcite, cancrinite. In volcanic rocks.
OLIGOCLASE
(Na,Ca)(Si,Al)4O8
(Tectosilicate, plagioclase, An10-An30)
photo
Colorless, clouded (alteration).Tabular, // to (010), prismatic elongated. Common chemical zoning.{001} perfect, {010} good, {110} poorAlbite polysynthetic. Pericline polysynthetic. Carlsbad penetrationInclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.008
1st order grey or white;
Optic related to anorthite content
L(-) to L(+)
nx=1.538
ny=1.542
nz=1.546
(Data for An20)
B(+) or B(-)
Triclinic
2Vx=87°
r>v weak
(Data for An20 oligoclase low temp.)
In plutonic rocks, granite, granodiorite, pegmatites, syenite. Metamorphic medium and high grade. Volcanic: rhyolite.
Altered to calcite, sericite, zeolites, muscovite, paragonite, kaolinite, scapolite, prehnite, pyrophyllite
OBSIDIAN
A volcanic glass containing crystallites of feldspar, tridymite, cristobalite
photo
Colorless, pale grey, pale yellow brown     n=1.482 (0 weight % H2O), 1.486 (0.35 weight % H2O)Isotropic
 Volcanic. Rhyolitic lava
OLIVINE
(Nesosilicates series name. See Fayalite, Forsterite)
camera camera
Colorless, pale yellow; darker with higher Fe, reddish or black due to impuritiesBipyramidal, stubby prismatic. Grains. 6 or 8 sidedPoor cleavage {010}, {110 usually not seen}.
Irregular fractures with alteration.
Rare simple twinning {100}, {011}, {012}// ext.
Length fast or length slow
Δn=0.035-0.052
Up to vivid 3rd order colors
H(+)
nx=1.635-1.827
ny=1.651-1.869
nz=1.670-1.879
B(+) or B(-)
Orthorhombic
2Vx=46°-98°In mafic and ultramafic rocks: basalt, dacite, dunite, gabbro, peridotite, pyroxenite
In volcanic rocks. Fayalite in syenite, nepheline syenite, phonolite, trachyte, andesine, dacite
Forsterite in metamorphosed dolomite.
Altered to iddingsite, serpentine (chrysotile, lizardite, antigorite).
OMPHACITE
(Ca,Na)(Mg,Fe++,Fe+++,Al)Si2O6
(Inosilicate, sodic-calcic clinopyroxene)
photo
Colorless to pale green.
Weak Pl. X= colorless, Y= very pale green, Z= very pale green, blue green
Stubby prismatic, 4 or 8 sided sectionsBasal section: cleavages intersect at ~87° // to {110}
parting // {100}
Simple and lamellar on {100}Ext. basal: symmetrical
// (100): //
// (010): 34°-48°
Length slow // c
Δn=0.012-0.028Upper 1st order, lower 2nd orderH(+)
nx=1.662-1.701
ny=1.670-1.712
nz=1.685-1.723
B(+)
Monoclinic
2Vz=56°-84°In eclogite with garnet, plagioclase, quartz, orthopyroxene, kyanite, Fe-Ti oxides. Also in glaucophane schist, amphibolite.
Altered to fibrous amphibole
OPAL
SiO2.nH2O
(Oxide, Quartz group)
Colorless, grey, brown.Colloform.None   M(-)
n=1.43-1.46
R.I. decreases when H2O increases
Isotropic
Amorphous
 Volcanic. Plutonic. Hydrothermal, Sedimentary.
Replaced by quartz, chalcedony.
ORTHOCLASE
KAlSi3O8
(Tectosilicate. K feldspar, Or100-Or85)
photo
Colorless, pale greyish. Often turbid.
Antiperthite: exsolution of K feldspar in Na plagioclase
Perthite: exsolution of Na Plagioclase.
Tabular, prismatic, elongated xls.{001} perfect. {010} good, intersect at 90°Simple twin: Carlsbad, Manebach, Baveno.Inclined 5°-6° to {001} cleavage.
Extinction could be 13° in Na cryptoperthites.
Δn=0.005-0.008
low: up to 1st order grey
L(-)
nx=1.524-1.526
ny=1.518-1.530
nz=1.521-1.533
B(-)
Monoclinic
2Vx=40°-~70°In felsic plutonic rocks. In granite, granodiorite, syenite. Also in metamorphic rocks. Authigenic in sedimentary rocks and hydrothermal veins: monoclinic adularia with rhombic cross section
Altered to clay and sericite.
ORTHOPYROXENE
(Inosilicate. A series in the Pyroxene supergroup
Hypersthene, Enstatite, Ferrosilite)
(Mg,Fe)SiO3
photo photo
Pale green.
With weak pinkish to greenish pleochroism.
Stubby prismatic. Basal sections 4 or 8 sided. Longitudinal sections are rectangularTwo good prismatic cleavages parallel to the {210} prism faces that intersect at ~90° (87°-93°)Rare {010}Longitudinal sections exhibit one cleavage and // extinction
Length slow
Δn=0.007-0.020
Usually up to first order yellow, or lower
M(+) H(+)
nx=1.649-1.768
ny=1.653-1.770
nz=1.657-1.788
R.I. increasing with increasing Fe content
B(+) or B(-)2Vz=50°-132°Enstatite (Mg px) is common in mafic intrusive rocks (gabbro, norite). Ferrosilite (Fe px) is found in more siliceous igneous rocks (diorite, syenite). Orthopyroxene is common in high grade regional metamorphic rocks
Altered to serpentine, talc or fine grained amphibole
(Distinguished from clinopyroxene by: 1) lower birefringence, 2) parallel extinction, 3) pale color, weak pleochroism, 4) most common orthopyroxene is optically negative, and 5) high 2V angle).
OXYHORNBLENDE
(Na,K)0-1Ca2(Mg,Fe++,Fe+++,Al)5(Si,Al)8O22(O,OH)2
(Basaltic hornblende. Inosilicate, clinoamphibole. Not an IMA mineral)
Brown, reddish brown. Zoning is common. Black iron-oxides rim.
Strong Pl. X= pale yellow, yellow, pale brown, greenish yellow, Y= brown, reddish brown, brownish green, Z= dark brown, dark reddish brown, dark green brown
Often euhedral in volcanic rocks, prismatic.{110} intersects at 56° and 124°.Simple or lamellar on {100}Symmetrical (basal section).
Inclined in sections // (010): 0°-18°
Length slow
Δn=0.018-0.083, masked by the strong color of the mineral. Upper 2nd order, 3rd order, 4th orderH(+)
nx=1.65-1.72
ny=1.67-1.78
nz=1.68-1.80
B(-)
Monoclinic
2Vx=56°-88°
r<v weak
In volcanic and shallow intrusive rocks: trachyte, basalt, andesite, latite, dacite, rhyolite.
Altered to biotite, chlorite.
PARAGONITE
NaAl2[]AlSi3O10(OH)2
(Phyllosilicate, a dioctahedral mica)
ColorlessFlakes{001} perfect{001}Ext. // cleavage. Inclined ext. <3°.
Δn=0.029-0.036
Up to upper 2nd order
(M+)
nx=1564-1580
ny=1.594-1.609
nz=1.600-1.609
B(-)
Monoclinic
2Vx=0°-40°
r>v moderate
Phengite and paragonite in low grade to high grade metamorphic rocks. Phyllite, schist, gneiss. Quartz veins.
PECTOLITE
(Inosilicate, Wollastonite group)
photo
ColorlessAcicular, radiating2 perfect cleav. {100} and {101} intersect at 95°~// {100} rareExt. ~//. Length slow.
Sections cut // (010): inclined ext 16°
Δn=0.030-0.038
Up to upper 2nd order
(M+)
nx=1.592-1.610
ny=1.603-1.615
nz=1.630-1.645
B(+)
Triclinic
2Vz=50°-63°
r>v or r>v
In basalt. With zeolites, calcite, prehnite, datolite.
In phonolite. In serpentinites, nepheline syenite. In skarn and Ca-rich metamorphic rocks.
PERICLASE
MgO
(Oxide)
Colorless
Pale yellow or brown when high Fe
No Pl.
Cubic, anhedral, surrounded with fibrous brucitePerfect {001}   H(+)
n=1.736
Up to 1.756 with high Fe content
Isotropic
Cubic
 High temperature metamorphosed dolomite.
With calcite, forsterite, humite, serpentine, brucite, spinel.
Altered to fibrous brucite.
PERROUDITE
Hg5Ag4S5(I,Br)2Cl2
Bright red, orange red
Strong Pl. X=dark brownish red, Y=yellow, Z=brownish-yellow
Prismatic on [001], flattened on {100}, (010)Perfect {100}May be contact-twinned with composition plane
0hl
 Δn=2.30H(+)
nα=2.300
nβ=2.400
B(+)
Orthorhombic
2V=70° (measured)
r>v, very strong
Secondary supergene mineral. With Tennantite, Iltisite, Capgaronnite. With Silver halides.
Photosensitive
PHLOGOPITE
KMg3AlSi3O10(OH)2
(Phyllosilicate dioctahedral mica. A series name in the mica group)
photo
Colorless, pale brown
Color zoning
Pl. X= colorless, pale yellow, light brown, greenish brown, pale green, Y=Z= brown, olive brown, dark green, dark red brown
Bladed, flakes, hexagonal{001} perfect{001}, {110}Ext. //
Length slow
Δn=0.028-0.049
2nd order to 3rd order.
L(-) L(+) M(+)
nx=1.53-1.59
ny=1.56-1.64
nz=1.56-1.64
B(-)
Monoclinic
2Vx=0°-15°
v>r
In metamorphosed carbonates, marble, peridotite, lamprophyre, volcanic leucite bearing rocks.
PIEMONTITE
Ca2(Al,Mn+++,Fe+++)3Si3O11O(OH)
(Sorosilicate. Epidote group)
(There is also Piemontite-Pb, Piemontite-Sr)
Reddish
Distinct Pl. X=yellow, orange, pink, Y=violet, red, Z=deep red, brownish red, pink
Color zoning.
prismatic, columnar, bladed, elongated, acicular. Rectangular or 6-sided sections.{001} perfectLamellar {100} rareExt. in (010) 13°-32° from trace of cleavage. Length fast or length slow
(Thulite ext. is //)
Δn=0.025-0.073
Δn increases with Fe
3rd order, 4th order
H(+)
nx=1.730-1.794
ny=1.740-1.807
nz=1.762-1.829
B(+) or B(-)
Monoclinic
2Vz=64°-106°
r>v, also r<v
Low to medium grade regional metamorphic rocks: phyllite, chlorite schist, glaucophane schist. Hydrothermal Mn deposits.
PIGEONITE
(Mg,Fe++,Ca)(Mg,Fe++)Si2O6
(Inosilicate, clinopyroxene)
Colorless, pale brownish or yellowish green
Rare weak Pl. X= colorless, pale greenish brown, pale greenish yellow, Y= pale brown, greenish brown, Z= colorless, pale yellow, pale green
Prismatic. Basal sections 6 or 8 sides, showing cleavagesGood // {110}, intersect at ~ 88°
Parting on {010} and {001}.
Simple or lamellar // {100} or {001}. Possible herring bone pattern.Symmetrical (basal section)
Inclined 32°-44° in sections // (010)
Δn=0.023-0.029
1st order yellow and red, up to lower 2nd order
H(+)
nx=1.682-1.732
ny=1.684-1.732
nz=1.705-1.757
B(+). Rarely U(+)
Monoclinic
2Vz=0-32°
r>v or r<v weak
Volcanic. Andesites. With augite, hypersthene.
In intermediate intrusive rocks.
PLAGIOCLASE
(Na,Ca)Al(Al,Si)Si2O8
(Tectosilicate. A series name. See Albite, Oligoclase, Andesine, Labradorite, Bytownite, Anorthite)
photo photo photo photo
See also MYRMEKITE intergrowths photo
Colorless. Clouded
Pale greyish, reddish, brownish due to inclusions. Zoning.
Tabular // (010). Prismatic elongated{001} perfect, {010} good, intersect at 93°-94°Albite // (010) polysynthetic Pericline, CarlsbadInclined.
Michel-Lévy method or Carlsbad-Albite method
Calculate with Ch. de Capitani
Δn=0.007-0.013
1st order grey or white. Anorthite up to 1st order yellow
L(-) L(+) M(+)
nx=1.527-1.577
ny=1.531-1.585
nz=1.534-1.590
R.I. increases with anorthite content
B(+) or B(-)
Triclinic
2Vx=45°-102° (high plagioclase)
2Vx=75°-102° (low plagioclase)
r<v or r>v
Plutonic, volcanic, metamorphic.
Albite: granite, granodiorite, rhyolite, pegmatite, syenite; low grade pelitic metamorphic
Oligoclase: granite, granodiorite, rhyolite, pegmatite, syenite; medium, high grade metamorphic.
Andesine: diorite, andesite; high grade metamorphic.
Labradorite, Bytownite: gabbro, basalt
Anorthite: mafic, ultramafic; amphibolite, metamorphosed carbonates
PREHNITE
Ca2Al2Si3O10(OH)2
(Transitional inosilicate - phyllosilicate structure)
photo
ColorlessPrismatic, tabular, radiating xls, lamellar, bow tieBasal {001} good Extinction ~ //
Wavy extinction.
Δn=0.022-0.051
Up to middle 2nd order
Δn increases with Fe content.
1st order
M(+) H(+)
nx=1.611-1.621
ny=1.615-1.637
nz=1.632-1.673
B(+)
Orthorhombic
2Vz=62°-69°
r>v weak
r<v strong
Cavities in mafic and volcanic rocks with zeolites, datolite, calcite, pectolite, chlorite, epidote
Metamorphic with pumpellyite, lawsonite, albite, epidote, chlorite, zeolites. Found in saussurite.
Altered to chlorite, zeolites
PUMPELLYITE
Ca2(Al,Fe++,Mg)Al2(SiO4)(Si2O7)(O,OH)2.H2O
(Sorosilicate group name)
(There is Pumpellyite-Al, -Fe++, -Fe+++, -Mg, -Mn++)
photo
Green, yellow, colorless (Mg-rich)
Color zoning related with higher Fe content.
Strong Pl. X= colorless, yellow, brownish yellow, greenish yellow, Y= light green, green, blue green, brownish yellow, Z= colorless, yellow, brownish yellow, reddish brown
Prismatic columnar, bladed, acicular xls{001} good // or inclined +4° to -34°
Length slow (Fe-rich elongated grains) or length fast:
Δn=0.01-0.02
1st order, 2nd order blue.
H(+)
nx=1.665-1.711
ny=1.670-1.718
nz=1.683-1.726
B(+) or B(-)
Monoclinic
2Vz=7°-110°
r<v very strong
Metamorphic. In prehnite-pumpellyite facies. In glaucophane schist, with glaucophane, lawsonite, clinozoisite, epidote, chlorite, actinolite, calcite, prehnite.
Also in basalt, gabbro.
Could alter to chlorite or actinolite.
PYROPHYLLITE
Al2Si4O10(OH)2
(Phyllosilicate
(Dioctahedral Al-member of the Pyrophyllite - Talc group)
ColorlessFoliated, scales, mica-like, columnar, prismatic, bent xls{001} perfect // extinction along trace of cleavage.
Length slow
Δn=0.044-0.062
3rd order, 4th order
L(+) M(+)
nx=1.552-1.556
ny=1.586-1.589
nz=1.596-1.601
B(-)
Monoclinic and Triclinic
2Vx=53°-62°
r>v
Hydrothermal alteration of Al-minerals: feldspars, andalusite, corundum, kyanite, topaz
With quartz, sericite, zoisite, clay minerals
QUARTZ
SiO2
(Oxide, Quartz group)
photo
See also MYRMEKITE intergrowths photo
Colorless.
Myrmekite: intergrowth quartz and plagioclase.
Graphic intergrowth K-feldspar.
Typically anhedral. Prismatic
α-Quartz hexagonal prism (low temp.)
β- Quartz bipyramid (high temp.)
None.
Poor on {101} or {100} ?
Dauphiné, Brazil {110}, Japan {112}Deformed quartz: undulatory extinction.
Length slow.
Δn=0.009
Low: 1st order grey-white, up to cream
L(+)
no=1.544
ne=1.553
U(+)
Trigonal
 Ubiquitous. Igneous. Metamorphic. Sedimentary. Hydrothermal.
RICHTERITE
Na(CaNa)Mg5Si8O22(OH)2
(Inosilicate, clinoamphibole)
Colorless, yellow, violet
Pl. variable: pale yellow orange, reddish, violet, blue
Prismatic, Bladed, fibrous{110} intersects at 56° and 124°.Simple or lamellar on {100}Inclined 5°-55° in (010)
Length slow. Lower extinction angle for rich Mg content
Δn=0.018-0.025
Upper 1st order, mid 2nd order
M(+) H(+)
nx=1.60-1.69
ny=1.61-1.70
nz=1.62-1.71
B(-)
Monoclinic
2Vx=55°-76°
r<v, stronger with Fe content
In metamorphosed limestone, skarn.
RIEBECKITE
[]Na2(Fe++3Fe+++2)Si8O22(OH)2
(Inosilicate, clinoamphibole. Glaucophane - Riebeckite series)
(There is also Magnesioriebeckite)
Dark blue.
Strong Pl. X= dark blue, Y= reddish blue, grey blue, Z= blue, yellow green, yellow brown
Bladed, prismatic.
Fibrous crocidolite. Rhombic basal section
{110} intersects at ~ 55° and 125°Rare. Simple or lamellar on {100}Inclined ext. in (010) less than ~22°. Length fast.Δn=0.006-0.017
Middle to upper 1st order
H(+)
nx=1.690-1.702
ny=1.690-1.712
nz=1.702-1.719
B(-). Or B(+) when Mg rich.
Monoclinic
2Vx=0°-135°
r<v strong (+)
r>v strong (-)
In alkali granite, syenite, peralkaline rhyolite, trachyte. High pressure metamorphic rocks.
RUTILE
TiO2
(Oxide)
camera
Reddish, brownish, almost opaque. Pleochroism (yellow, brown-red) > o (yellow, brownish, greenish). Zoning.Prismatic, elongated, octagonal cross section, acicular{110} good, {100} distinct{101}, knee shaped or cyclic twins//, length slowΔn=0.286-0.296
High upper order grey, white
VH(+) (extreme)
no=2.605-2.613
ne=2.899-2.901
U(+)
Tetragonal
May be anomalously biaxial with 2V=10°Igneous. With hornblende, biotite.
Metamorphic, high temperature metamorphic.
Rarely altered to titanite, leucoxene.
Polymorph with Anatase and Brookite.
SANIDINE high
(K,Na)(Si,Al)4O8
(Tectosilicate. K feldspar, Ab0-Ab33)
photo
Colorless, white, yellowishPhenocryst., radiated, acicular{001} perfect, {010} distinct{010} // simple Carlsbad twinsSections // (010): 20°Δn=0.005-0.006
Low, 1st order.
L(-)
nx=1.518-1.521
ny=1.523-1.525
nz=1.524-1.526
Monoclinic
B(-)
2Vx=15°-63°
r>v weak
Siliceous volcanic rocks. Spherulites in volcanic glasses.
Altered to kaolin, sericite, cryptocrystalline silica
SANIDINE low
(K,Na)(Si,Al)4O8
(Tectosilicate. K feldspar, Ab0-Ab33)
photo
Colorless
Zoning
Prismatic, tabular xls. Crosse section: 4 or 6 sided.{001} perfect. {010} good, intersects at 90°Carlsbad twinsSections // to (010): Inclined ext. 5°-9° to {001} cleavage.
Sections normal to (010): // extinction to cleavage
Δn=0.004-0.006
Low, 1st order.
L(-)
nx=1.518-1.524
ny=1.522-1.529
nz=1.522-1.530
Monoclinic
B(-)
2Vx=18°-42°
Volcanic: rhyolite, rhyodacite, phonolite, trachyte. With cristobalite. In high temperature metamorphic.
Altered to sericite and clay
SAPPHIRINE
(Mg,Al)8(Al,Si)6O20
(Inosilicate, aenigmatite - sapphirine - surinamite group)
camera
Colorless, blue, pinkish
Pl. X= colorless, pale pink, pale yellow, yellowish green, greenish blue, greenish grey, Y= sky blue, pale blue, lavender blue, grey blue, green, Z= blue, reddish blue, blue green, pale green
Tabular, prismatic, ~ elongate{010} poorLamellar twinning on {010} rareLength slow if xls elongate // c.
(010) ext.: 6°-15°
Δn=0.005-0.015
1st order
H(+)
nx=1.701-1.731
ny=1.703-1.741
nz=1.705-1.745
B(-) or B(+)
Monoclinic
2Vx=47°-114°
r<v strong
High-grade contact or regional metamorphism
With cordierite, kyanite, sillimanite, corundum, spinel, Ca-plagioclase, almandine, orthopyroxene, anthophyllite, hornblende. Usually not with quartz.
SCAPOLITE
(Tectosilicate group name)
(Marialite - Mizzonite . Meionite)
photo
Colorless, cloudy.Prismatic, bipyramidal prismatic, anhedral.
Inclusions: quartz, calcite, feldspar
2 cleav. // to {110} good
2 cleav. // to {100} distinct
Intersect at 45° on basal section
 Ext. //
Length fast
Δn=0.004-0.038
1st order, 2nd order
L(-) L(+) to M(+)
no=1.539-1.600
ne=1.531-1.564
U(-)
Tetragonal
May be biaxial with 2V<10°Metamorphic. Skarn, marble. With garnet, diopside, actinolite, titanite, calcite, vesuvianite. In amphibolite with hornblende Ca clinopyroxene, epidote, titanite. Also volcanic.
Altered to sericite, calcite, chlorite, epidote, zeolites
SERPENTINE group
(Mg,Fe++,Ni)3Si2O5(OH)4
(Inosilicate. Chrysotile, Antigorite, Lizardite)
photo
Colorless, pale green
Weak Pl: colorless, pale yellow green, pale green.
Prismatic. Fibrous (Chrysotile). Netlike pattern (Lizardite). Foliated (Antigorite){001} perfect (antigorite) Ext. // to the length of fibers (chrysotile)
Length slow (antigorite)
Δn=0.001-0.010
1st order grey or white
L(-) L(+) M(+)
nx=1.529-1.595
ny=1.530-1.603
nz=1.537-1.604
R.I. increases with Fe content
B(-)
Monoclinic. Also triclinic, hexagonal
2Vx=20°-50°
r>v or r<v
Hydrothermal alteration of peridotite, pyroxenite. Produced from alteration of olivine, pyroxene. With magnetite, talc, calcite, brucite, chlorite, chromite.
In metamorphosed carbonates. With calcite, forsterite, dolomite, magnesite.
Altered to chlorite.
SIDERITE
Fe++CO3
(Carbonate, calcite group)
Colorless, grey, pale yellow, brownish
Pleochroic o>e
Rhombohedral, botryoidal{101} perfectLamellar on {01-12} rareExtinction symmetrical or inclined to cleavage tracesΔn=0.240
Very high upper order white
H(+)
no=1.875
ne=1.635
U(-)
Hexagonal, Trigonal
 In sedimentary iron formations. Gangue mineral in high temperature hydrothermal veins
Altered to goethite; also to hematite or magnetite
SILLIMANITE
Al2SiO5
(Nesosilicate sillimanite - andalusite - kyanite group)
photo
Usually colorless. Could look greyish due to spray of inclusions. Pale brown (fibrolite).
Pl. (colored varieties) X= yellow or colorless pale yellow, Y= green yellow or colorless or pale yellow, Z=colorless or violet brown or blue
Slender prismatic xls, elongated on c, fibrous (fibrolite): Rhombic shaped basal {110}.{010} good // extinction
Length slow
Δn=0.018-0.022
Up to lower 2nd order. Fibrolite: 1st order yellow.
M(+) H(+)
nx=1.653-1.661
ny=1.657-1662
nz=1.672-1.683
B(+)
Orthorhombic
2Vz=21°-30°
r>v strong
In high temperature rocks. Metamorphic. In mica schist, gneiss, hornfels. Also in granite, pegmatite.
With kyanite, andalusite, staurolite, muscovite, biotite, feldspar, cordierite, corundum, garnet. Altered to sericite
SODALITE
Na8Al6Si6O24Cl2
(Tectosilicate. feldspathoid, sodalite group: sodalite, nosean, haüyne)
photo photo
Colorless, grey, very pale blue. Dark rim. No pleochroism.Six sided cross sectionPoor {110}{111} difficult to observe  M(-)
n=1.483-1.490
Isotropic
Cubic
 Silica deficient alcalic igneous rocks. Volcanic, phonolite, trachyte. Plutonic, nepheline syenite. With nepheline, leucite, sanidine Altered to zeolite (fibrous), clay, calcite, cancrinite
SPINEL
(Mg,Fe++) Al2O4
(Oxide. a group name including spinel series, magnetite series, chromite series. Here: spinel series)
Colorless, pinkish, bluish, greenish grey (spinel), deep green (hercynite)Octahedral xls. Square, rhombic, triangle cross section.None. Parting on {111}Contact plane {111} difficult to observe  VH(+)
n=1.719 Spinel
n=1.835 Hercynite
n=1.805 Gahnite
n=1.920 Galaxite
Isotropic
Cubic
 High grade metamorphic with andalusite, kyanite, sillimanite, corundum, cordierite, orthopyroxene
Regional metamorphosed carbonates rocks, with chondrodite, phlogopite, calcite, forsterite
In contact metamorphic, granulite. Hercynite, Picotite in ultramafic. Gahnite in granite pegmatite, and hydrothermal. Galaxite with Mn minerals, spessartine, rhodonite.
SPODUMENE
LiAlSi2O6
(Inosilicate, Li clinopyroxene)
Usually colorless.
Some gems with green or lilac. Pl. (colored specimens): green, lilac shades
Prismatic, lamellar. Octagonal section.Basal section: cleavages {110} intersect at ~87.
Parting on {010} and {100}.
Twin. on {100}Basal (2 cleavages): symmetrical ext.
Longitudinal // (010): 20°-26° inclined ext.
Length slow
Δn=0.014-0.027 Upper 1st order to mid 2nd orderM(+) H(+)
nx=1.648-1.668
ny=1.655-1.671
nz=1.662-1.682
B(+)
Monoclinic
2Vz=58°-68°In Granitic pegmatite (Li-rich). With quartz, feldspar, beryl, tourmaline, lepidolite.
Altered to Li-mica, albite, eucryptite
STAUROLITE
(Fe++,Mg,Zn)2Al9(Si,Al)4O22(OH)2
(Nesosilicate)
(There is also Magnesiostaurolite, Zincstaurolite)
photo
Pale yellow, honey yellow, yellow brown. Color zoning.
Distinct Pl. X= colorless, pale yellow, Y= pale yellow, yellowish brown, Z= golden yellow, reddish brown
Prismatic xls. Rhombic shape. Twins. Inclusions.{010} poorPenetration twins {031}: 90° Brittany cross.
Penetration twins {231}: 60° St Andrew cross.
Contact {031} rare
// extinction (longitudinal).
Symmetrical (basal)
Length slow
Δn=0.011-0.014
Up to 1st order white, yellow
H(+)
nx=1.736-1.747
ny=1.742-1.754
nz=1.748-1.761
B(+)
Monoclinic, pseudo-orthorhombic
2Vz=80°-90° 2V decreases when Fe increases.
r>v weak to moderate
Medium grade regional metamorphic. Mica schist.
With garnet, muscovite, biotite, andalusite, sillimanite, kyanite, chloritoid, cordierite, chlorite.
STILBITE
(Ca0,5,Na,K)9[Al9Si27O72].28H2O
(Tectosilicate, zeolite, heulandite - stilbite - brewsterite group)
(There is Stilbite-Ca, Stilbite-Na)
ColorlessTabular,radiating bundles of xls, bow tie{010} good{100} cruciform penetration twins~ inclined, ~ // ext. to (010)
Length fast or length slow
Δn=0.006-0.014
1st order
L(-) M(-)
nx=1.484-1.500
ny=1.492-1.507
nz=1.494-1.513
B(-)
Monoclinic
2Vx=30°-49°
r<v
In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks
Altered to clay, zeolites
STILPNOMELANE
K(Fe++,Mg,Fe+++,Al)8(Si,Al)12(O,OH)27.2H2O
(Phyllosilicate)
photo
Pale yellow, brown, dark brown, green
Basal sections are dark
Pl. X= pale yellow, golden yellow, Y=Z= brown, reddish brown, greenish brown, black
Bladed, elongated, thin prismatic, sheaflike aggregates{001} and {010} intersect at 90°
Basal cleav. less perfect than in biotite.
 Trace of basal cleavage // and length slow
(no or poor bird-eye ext.)
Δn=0.030-0.110
Upper 2nd order, 3rd order, High upper order 4th order, creamy 5th order and 6th order
L(+) M(+) H(+)
nx=1.543-1.634
ny=1.576-1.745
nz=1.576-1.745
R.I. increases with Fe
B(-), appears U(-)
Triclinic (pseudomonoclinic)
Sections cut to (001) appear isotropic
2Vx=~0°Low grade regional metamorphism. With chlorite, muscovite, garnet, amphibole, glaucophane, calcite, epidote group, pumpellyite. In metamorphosed iron formations.
Altered to clay, chlorite, iron oxides
TALC
Mg3Si4O10(OH)2
(Phyllosilicate
(Pyrophyllite - Talc group)
photo
Colorless
Weak Pl. colorless, pale yellow green, pale green
Flakes, foliated{001} perfect // extinction
Length slow
Δn=0.05
3rd order
L(+) M(+)
nx=1.539-1.550
ny=1.589-1.594
nz=1.589-1.600
R.I. increases with Fe
B(-)
Triclinic
2Vx=0°-30°
r>v weak to moderate
Hydrothermal altered mafic and ultramafic: With serpentine, magnesite.
Metamorphic. Blue schist with glaucophane. Mica schist. Talc schist, with magnetite, tremolite, chlorite, anthophyllite, serpentine. In metamorphosed dolomite with calcite, dolomite, tremolite.
THOMSONITE
Ca2Na[Al5Si5O20].6H2O
(Tectosilicate, zeolite, natrolite group)
photo
ColorlessPrismatic, columnar, fibrous, radiating aggregates
{010} perfect and {100} intersect at 90°{110} rareExt. //
Length slow
Δn=0.006-0.021
1st order grey to yellow
L(-)
nx=1.497-1.530
ny=1.513-1.533
nz=1.518-1.544
B(+)
Orthorhombic, pseudotetragonal
2Vz=42°-75°In lacustrine sediments. In basalt, gabbro, serpentinite. Volcanic altered rocks.
THULITE
Ca2Al3[Si2O7][SiO4]O(OH)
(Sorosilicate, a pink variety of orthozoisite with up to 2% of Mn)
photo photo
Colorless to pleochroic. X= deep pink, Y= pale pink, Z= pale yellow, yellowPrismatic, columnar, bladed, anhedralPerfect // {100} // extinction in (010)Δn=0.006-0.018
1st order, 2nd order
Slightly anomalous since superposition of color to birefringence.
H(+)
nx ~1.700
ny ~1.703
nz ~1.708
(thulite frpm Øvstebø)
B(+)
Orthorhombic
2Vz ~71°, variable due to chemical zoning
(thulite from Øvstebø)
In pegmatite and hydrothermal veins.
TITANITE
CaTiSiO5
(Nesosilicate)
photo photo
Brown. Rarely yellow or colorless.
Weak Pl. X= colorless, pale yellow, Y= yellow brown, pink, greenish yellow, Z= orange brown, greenish brown, green, red
Prismatic rhombic shaped xls
Good prismatic {110}Simple twins {100}
Lamellar {221}
Inclined 36° to 51° to the trace of cleavage.
Rhombic sections: symmetrical ext.
Length fast
Δn=0.100-0.192 Extreme.
High upper order grey.
H(+) VH(+)
nx=1.843-1.950
ny=1.870-2.034
nz=1.943-2.110
B(+)
Monoclinic
2Vz=17°-40°
r>v very strong
Igneous, syenite, monzonite, granodiorite, diorite. With biotite, hornblende. Metamorphic, glaucophane schist, mica schist, amphibolite, gneiss, skarn, marble. Volcanic: phonolite.
Altered to leucoxene.
TOPAZ
Al2SiO4(F,OH)2
(Nesosilicate)
Colorless
Pl. X=Y= ~yellow, Z= ~pink
Prismatic. Square or rhombic basal section{001} perfect // ext. in longitudinal sections
Symmetrical on rhombic section.
Length fast on cleavage. Length slow on elongation.
Δn=0.008-0.011
1st order white or pale yellow
M(+)
nx=1.606-1.634
ny=1.609-1.637
nz=1.616-1.644
B(+)
Orthorhombic
2Vz=48°-68°
r>v
Plutonic, volcanic rocks. In rhyolite. Hydrothermal with W, Sn, Mo, Au. metamorphic quartzites, schists.
With muscovite.
Altered to sericite, clay.
TOURMALINE
Na(Mg,Fe,Li,Al)3Al6(Si6O18)(BO3)3(OH,F)4
(Cyclosilicate group name: Schorl, Dravite, Elbaite, etc.)
Schorl NaFe3Al6(Si6O18)(BO3)3(OH)4
Dravite NaMg3Al6(Si6O18)(BO3)3(OH)4
Elbaite Na(Li,Al)3Al6(Si6O18)(BO3)3(OH)4
photo photo
Variable, grey, blue, green, pink, colorless. Concentric zoning.
Strong pleochroism o>e e= grey, green, blue, yellow, brown, pink; o= colorless, light colored
Prismatic. Acicular. Hexagonal, rounded triangular cross sectionPoor {110} {101}
Fractures perpendicular to xl length
Rare {101}// extinction in longitudinal section.
Length fast.
Δn=0.017-0.035
1st order, 2nd order
M(+) H(+)
no=1.63-1.70
ne=1.61-1.68
R.I. increases with Fe
U(-)
Hexagonal Trigonal
Occasionally biaxial with 2V~10°Granitic pegmatite, granite, granodiorite. Metamorphic, schist, gneiss, phyllite. Hydrothermal. Also in greisen.
Altered to sericite, chlorite, lepidolite, talc.
TREMOLITE
[]Ca2Mg5Si8O22(OH)2
(Inosilicate. Clinoamphibole, Tremolite - Actinolite - Ferro-actinolite series.)
photo
Colorless
Weak green Pl.
Prismatic columnar, bladed, acicular, fibrous. Rhombic basal section.{110} intersects at 56° and 124°. Visible on basal sectionsSimple or {100} lamellar, // to the long diagonal of basal sectionInclined section (010): 17°-21°.
Sections // to (100) show // extinction
Length slow.
Δn=0.022-0.027. Up to mid 2nd order.M(+)
nx=1.600-1.620
ny=1.612-1.630
nz=1.625-1.645
R.I. increases with increasing Fe content.
B(-)
Monoclinic
2Vx=84°-88°
r<v weak
Low grade and contact metamorphic metamorphic limestone. With calcite, dolomite, forsterite, garnet, diopside, wollastonite, talc, epidote. Also in mafic and ultramafic rocks. In blue schists.
Altered to chlorite, talc, carbonates.
TRIDYMITE (β-TRIDYMITE)
SiO2
(Oxide, Quartz group)
ColorlessHexagonal, anhedralPoor prismatic cleavage. Often none.{106}Elongated xls // ext.
Length fast
Δn=0.002-0.004M(-)
nx=1.471-1.479
ny=1.472-1.480
nz=1.474-1.483
B(+)
Orthorhombic (pseudohexagonal)
2V=40°-90°Volcanic. Plutonic.
In basalt with quartz, cristobalite, fayalite, sanidine, topaz, hematite, garnet.
β-Tridymite alters to α-Tridymite.
VESUVIANITE
Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4
(Sorosilicate)
Colorless. Pale yellow, brown, green
Anomalous interference colors. Weak Pl. o>e
Stubby tetragonal prismatic, anhedralPoor {110} Elongate xls: length fast. Ext. //Δn=0.001-0.020
Low 1st order, middle 1st order
H(+)
no=1.702-1.795
ne=1.700-1.775
U(-) or U(+)
Tetragonal
 Contact metamorphic limestone. With garnet, grossular, diopside, wollastonite, tremolite, calcite, epidote.
In nepheline syenite. In altered gabbro, peridotite.
WINCHITE
[]{CaNa}{Mg4Al}(Si8O22)(OH)2
(Inosilicate, Amphibole group, winchite subgroup)
photo
       Monoclinic  
WOLLASTONITE
CaSiO3
(Inosilicate, wollastonite group)
ColorlessPrismatic, columnar, bladed, fibrous{100} perfect. {001} and {-102} intersect at 84.5°. {-102} and {100} intersect at 70°{100}// ext. in section (100)
Other sections are inclined.
Length slow.
Δn=0.013-0.017
1st order yellow
M(+)
nx=1.616-1.645
ny=1.628-1.652
nz=1.631-1.656
B(-)
Triclinic
2Vx=36°-60°In metamorphic limestone and dolomite. With calcite, dolomite, tremolite, epidote, grossular, augite, monticellite, forsterite
XENOTIME
YPO4
(Phosphate)
Colorless, yellow, pale brown
Weak Pl. o= pale pink, yellow brown, yellow, e= pale brownish yellow, greyish brown, greenish
Prismatic, tetragonal, elongate, radial aggregates{100}Simple on {101} elbow shaped twins// ext.
Length slow
Δn=0.070-0.107
High upper order
H(+)
no=1.690-1.724
ne=1.760-1.827
U(+)
Tetragonal
 Plutonic. Granite, syenite, granodiorite, pegmatite. Metamorphic, in mica schist, gneiss, marble
ZIRCON
(Zr,Hf)SiO4
(Nesosilicate)
camera camera
Colorless, pinkish, pale brown, yellow
Weak Pl. o<e
Stubby prismatic, anhedral. Tetragonal xls with pyramidal terminationsPoor {110} and {111}{111} rareLongitudinal sections show // extinction
Length slow
Δn=0.042-0.065.
High upper order. Up to 3rd order, 4th order
H(+) VH(+)
no=1.923-1.960
ne=1.961-2.015
U(+)
Tetragonal
Anomalous 2V=0°-10°Plutonic felsic rocks. In granite, syenite, granodiorite, pegmatite. Metamorphic: in mica schist, gneiss, schist.
Inclusion with halo in biotite, cordierite, chlorite, tourmaline
With quartz, feldspar, biotite, hornblende.
ZOISITE
Ca2Al3[Si2O7][SiO4]O(OH)
(Sorosilicate)
Colorless, grey, grey-green.
XPL: anomalous blue interference colors unevenly distributed.
Pl. (Thulite) X= pink, Y= pale pink, colorless, Z= pale yellow, pink zones
Prismatic, columnar, bladed, acicular, anhedralPerfect // {100} // extinction in (010).
Length fast:zoisite
Length slow: Fe-rich zoisite
Both elongations in zoned xls
Δn=0.003-0.020
1st order, 2nd order
H(+)
nx=1.685-1.705
ny=1.688-1.710
nz=1.698-1.725
R.I. increases with Fe content
B(+) Ferrian zoisite
Also B(-) Orthorhombic
2Vz=0°-50°
(> 60° with Fe)
r>v (zoisite)
r<v (ferrian zoisite)
Low grade to medium grade metamorphic: schist, gneiss, marble
With Na plagioclase, garnet, biotite, hornblende, muscovite, calcite

Bibliography

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