plagioclase thin section PPL and XP Transmitted Light Reflected Light Definitions of Properties About Contact Us
Identify minerals under transmitted light

Select below the properties that you can see under the microscope. The table will then display all the minerals that match that specific combination of properties.

Properties in bold are particularly distinct for that mineral. Click on the mineral name to see pictures.

Mineral properties
Mineral Colour Birefringence Relief Noteworthy Features Cleavage Extinction Habit 2V Angle Optic Sign Found In Associated Minerals Mineral Group Crystal System
Actinolite Colourless to Green Pleochroic. More Green for more Fe-rich Moderate. 0.027 up to mid 2nd order Moderate C to Epidote: less Yellowish and lower relief / Length Slow Good. 2 sets at 124° Inclined 30° max / Typically 15° Fine Prisms / Laths / Fibrous / Needle-like Large 75-80° Negative Metamorphic (Green and Blueschist, Serpentinite, Marbles) Actinolite Amphibole Monoclinic
Aegirine Bright Green / Yellow / Brown / Pleochroic High. 0.04-0.06 up to 3rd or 4th High May occur as rim on other green pyroxenes / Length Fast Good. 2 sets at 87° Inclined 0-10° Needle Prisms / Hexagonal Large 80-90° Negative Igneous Albite Epidote Biotite Sphene Talc Calcite Chlorite Quartz Sericite Clinopyroxene Monoclinic
Aenigmatite Dark Brown to opaque / Strongly Pleochroic in very thin sections Very High High to Very High Intergrowths with Arfvedsonite are common / Opaque to smoky haloes around Orthite inclusions / Polysynthetic Twinning Good. 2 sets at 66° Inclined 4-45° Columns / Needles Small to Moderate 27-55° Positive Igneous (Felsic, Na-rich rocks) Anorthoclase Arfvedsonite Clinopyroxenes Nepheline Sapphirine Supergroup Triclinic
Akermanite Colourless / Weakly Pleochroic Low Moderate May have anomalous interference colours (Purple Blue) / Interpenetrating twinning / Length Fast Poor. 2 sets Straight Plates Uniaxial Positive Igneous (Silica-undersaturated Volcanic rocks) / Metamorphic Epidote Sphene Tourmaline Melilite Tetragonal
Albite Colourless Low. up to cream Very Low Albite Twinning lengthways / Carlsbad Twinning / Common in low-grade Metamorphic rocks with Chlorite, Muscovite and Actinolite / May occur as rims on more calcic plagioclase later replacement of feldspars in Igneous rocks. Perfect and Good. 2 sets at 86° Inclined 12-20° Prisms Large 70-80° Positive Igenous / Metamorphic Leucite Nepheline Olivine Titanaugite Plagioclase Feldspar Triclinic
Allanite / Orthite Yellow / Pink / Magenta / Deep Brown Pleochroism Moderate to High. 0.018-0.030 High Commonly zoned / with Epidote and Clinozoisite rims (due to radiation damage) / Rich in REE Poor Straight or Inclined Irregular Prisms / Needles Moderate to Large 40-80° Negative Igneous (Acid to Intermediate rocks) / Metamorphic (Low to High grade regional metamorphism) Biotite Cordierite Quartz Sericite Muscovite Epidote Monoclinic
Almandine Colourless / Reddish Isotropic High Porous texture / Heliocentric inclusion spirals None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Metamorphic (Low to high grade) Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass Garnet Cubic
Analcime / Analcite Colourless Very Weak (may be anomalous) Low Often in groundmass between Plagioclase grains in Dolerite and Basalt rocks / Replaces Leucite / Polysynthetic Twinning Poor Almost Isotropic Euhedral / Anhedral / usually deformed / Spheres Nearly Isotropic Negative Igenous (Basic volcanic rocks) Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass Zeolite Triclinic / Pseudo Cubic
Anatase Yellow Brownish / Blue / Opaque Very High Very High May have zoned colour distribution / Length Fast Perfect. 2 sets Straight Detrital / Granular / Needles Uniaxial Negative Sedimentary Oxide Tetragonal
Andalusite Colourless / Red / Yellow / Green / Pale Pink Pleochroic Low. 0.009-0.012 up to White Moderate May alter to Mica / Patchy Pink colouration / Graphite inclusions / Length Fast Good Straight Prisms / Cubes / Needles Large 70-90° Negative Metamorphic (Low-P metapelites) / rare in igneous Al Silicate Orthorhombic
Andesine Colourless Low. up to pale Gray Very Low Albite Twinning lengthways / Carlsbad Twinning / Often zoned / with Hornblende in Igneous rocks / Found in medium to high grade metamorphic rocks Perfect and Good. 2 sets at 86° Inclined 12-28° Prisms / Tabular / Laths Large 70-90° Negative Igenous / Metamorphic (Medium to High grade) Calcite Zeolite Plagioclase Feldspar Triclinic
Andradite Green to Brown Isotropic (may be anomalous) Very High Zonal growth rings / Mottled colour texture None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Metamorphic (Fe-metasomatosed skarn) Biotite Diopside Hornblende Hypersthene Olivine Plagioclase Garnet Cubic
Anhydrite Colourless Very Low Very High to Moderate Distorted cleavage planes / Alters to Gypsum with water / Polysynthetic Twinning Good. 3 sets Straight Granular / Needles Moderate to Small 42° Positive Sedimentary (Evaporites) Albite Almandine Chlorite Clinopyroxene Hornblende Kyanite MuscoviteK-Feldspar Orthopyroxene Plagioclase Quartz Staurolite Volcanic Glass Sulphate Orthorhombic
Anorthite Colourless Low. up to cream / Yellow Low Distinctive Albite Twinning lengthways / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / More commonly found in very high grade metamorphic rocks than in igneous rocks Perfect and Good. 2 sets at 86° Inclined 52° Prisms Large 80-90° Negative Igneous / Metamorphic (High grade) Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass Plagioclase Feldspar Triclinic
Anorthoclase Colourless Very Low Very Low to Low Cross Hatched twinning / Length Fast Good. 2 sets at 90° Plates / Lath-Like / Granular Moderate to Large 60-110° Positive / Negative Igneous (Na-rich Volcanic rocks) Alkali Feldspar Monoclinic
Anthophyllite Colourless Low to Moderate. 0.013 up to mid 2nd order Moderate Occurs in Mg-rich metamorphic rocks (e.g. low-grade metabasites) / Often with Talc / Like Actinolite but parallel extinction / Length Slow Good. 2 sets at 124° (Amphibole Cleavage) Straight Prisms Large 70-90° Positive Metamorphic (Low-P metapelites) Aegirine-Augite Calcite Melanite Nepheline Sanidine Sodalites Amphibole Orthorhombic
Antigorite Colourless to Pale Green / Weakly Pleochroic Very High Low to Moderate Fan-shaped multiple twins with undulose extinction / Grid texture in ultrabasic rocks / Length Slow Perfect Straight / May be Undulose Radiating / Flaky / Long Prisms / Scaly Small to Moderate 27-60° Negative Metamorphic (Low grade and Serpentinites) Serpentine Monoclinic
Apatite Colourless / Pale Red Grey or Brownish Very Low. 0.002 Gray Moderate Usually as tiny elongate crystals with rounded or hexagonal outline / Often as accessory mineral / Length Fast Poor. 2 sets Straight Hexagonal / Elongate Prisms / Laths / Oolitic spheres / Radiating branches Uniaxial Negative Igneous / Metamorphic / Sedimentary Albite Almandine Biotite Chlorite Quartz Rutile Sericite Phosphate Hexagonal
Apophyllite Colourless Very Low Low Perfect Straight Platy / Granular / Tabular Uniaxial Positive / Negative Igneous (Fractures and Amygdules in basic Volcanic rocks) Olivine Serpentine Titanaugite Tetragonal
Aragonite Colourless Very High. 0.155 Low to High No rhombohedral Cleavage / Simple to Lamellar twinning / Length Fast / Cavity Filling in volcanic rocks Poor Straight Prisms / Radiating needles Small 18° Negative Sedimentary (with organics) Carbonate Orthorhombic
Arfvedsonite Green / Purple / Brown / Dark Blue / Pleochroic Very High / May be Anomalous Moderate to High Poikilitic sieve texture / Simple Twinning / Length Fast Perfect and Good. 2 sets Inclined 65-80° Thick Columns / Elongate Prisms / Needles / Granular / Flaky Small to Large 0-100° Positive / Negative Igneous (Nepheline Syenite) Andalusite Biotite Garnet Hercynite Hypersthene Quartz K-Feldspar Muscovite Plagioclase Quartz Sillimanite Alkali Amphibole Monoclinic
Augite Group Colourless to Pale Green / Brown / Pleochroic Moderate. 0.018 Moderate to High Simple Twinning / May have zoned colour distribution / Relief changes depending on orientation / Alters to Amphibole, Chlorite, Epidote and Talc / Replaces Diopside in Limestones Good. 2 sets at 87° Inclined 35-50° / May be Undulose Prisms / Hexagonal / Needles Moderate 60° Positive Igneous (Alkaline basalts) / Metamorphic Almandine Also Garnet Clinozoisite Epidote Jadeite Lawsonite Omphacite Pumpellyite Rutile Zoisite Clinopyroxene Monoclinic
Barite Colourless Very High Moderate Kinking and crenulation / Polysynthetic Twinning / Length Fast Good. 3 sets Straight Flaky / Granular / Fibrous / Columns / Elongate Prisms / Platy / Radial Moderate 36-38° Positive Igneous / Metamorphic / Sedimentary (as gangue in hydrothermal deposits, in concretions in sandstone and in desert roses) Orthorhombic
Barrosite Group Blue Green / Pleochroic Very High Moderate to High May have pleochroic haloes / Use associated minerals to distinguish from other amphiboles / Alters to Actinolite, Antigorite, Chlorite / Length Slow Perfect. 2 sets at 124° Inclined 15-22° Short to Long Columns / Elongate Prisms / Needles Moderate to Large 65-90° Negative Metamorphic (Low grade) Augite Olivine Pigeonite Plagioclase Green Hornblende Amphibole Monoclinic
Beryl Colourless / Pale Blue to Pale Green / Weakly Pleochroic Low Very High to Moderate May be anomalously Biaxial / Length Fast Poor Straight Short to Long Prisms / Granular Uniaxial Negative Igneous (Granite pegmatites) / Metamorphic Hexagonal
Biotite Brown or Green / Pleochroic High. 0.028 Moderate to High Easily altered to Chlorites or Clays / More opaque in volcanic rocks / Mottled / Length Slow Perfect Straight or Inclined 5° Hexagonal / Plates Small 0-35° Negative Igneous / Metamorphic Biotite Mica Monoclinic
Bronzite Pale Green / Weakly Pleochroic Very High Moderate to High A variety of Enstatite / Zoning with Mg-rich core in Colcanic rocks / often with exsolution lamellae in Plutonic rocks / Alters to serpentine Good. 2 sets Short Columns / Elongate Prisms / Granular Large to Moderate 97-63° Positive / Negative Igneous (Basic to ultrabasic rocks) Hematite Quartz Topaz Tourmaline Orthopyroxene Orthorhombic
Bytownite Colourless Low. up to cream Low Albite Twinning lengthways / Carlsbad Twinning / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / Often with Clinopyroxene and/or Olivine in Igenous rocks. Perfect and Good. 2 sets at 86° Inclined 40-52° Rectangular Laths / Prisms Large 80-90° Negative Igenous / Metamorphic (High grade) Plagioclase Feldspar Triclinic
Calcite Colourless Very High. 0.172 Extreme pastel colours Low to High Twinkling Cleavage / Lamellar Twinning / Found infilling Fauna and Flora in carbonates / Length Fast Perfect. 3 sets (Rhombohedral) Straight Interlocked Grains / Fibrous / Oolitic spheres Uniaxial Negative Metamorphic / Sedimentary Carbonate Trigonal
Cancrinite Colourless / Pale Yellow Moderate. 0.018 Low Negative Often replaces Nepheline / Length Fast Perfect Straight Elongate Prisms / Laths / Fibrous Uniaxial Negative Igneous Almandine Also Garnet Clinozoisite Epidote Jadeite Lawsonite Omphacite Pumpellyite Rutile Zoisite Feldspathoid Hexagonal
Carbon (Organic) Brownish to Gray / Opaque Very Low to Very High As a black pigment in many organic rich rocks Not a crystal Granular (Small) Not a crystal Not a crystal Metamorphic (Low-grade) / Sedimentary (Organic rich) Amorphous
Cassiterite Gray / Yellow / Red / Brown / Weakly Pleochroic Very High Very High May have zoned colour distribution / Pleochroic haloes / Twinning / Length Slow Good Straight Granular / Prisms / Needles Uniaxial Positive Igneous (Pegmatitic Ore deposits) / Metamorphic (Greisen and contact skarn) Clinopyroxenes Leucite Melanite Nepheline Olivine Plagioclase Volcanic Glass Sanidine Titanaugite Tetragonal
Celadonite Green / Pleochroic Very High Moderate Pseudomorphs after Olivines / Length Slow Pefect Inclined 2-3° Radiating / Fine Grained Small 0-20° Negative Igneous (Cavity filling in basalts) / Metamorphic (Zeolite facies) Monoclinic
Chabazite Colourless Very Low to Low Very Low Mostly as subgrains / Simple Twinning Good Straight Cubes / Prismatic Small 0-30° Positive / Negative Igneous (Cavity and Fractures Filling in Volcanic rocks, in veins in plutonic rocks) Cubic Zeolite Trigonal
Chalcedony Colourless Low Very Low to Low Straight Needles / Radiating / Dense Uniaxial Positive Igneous (Fractures and Amygdules in Volcanic rocks) Chromite Hematite Magnetite Pentlandite Pyrite Pyrrhotite Rutile Tantalite Framework SiO2 Trigonal
Chlorite Group Colourless / Green Low or Very low. up to Gray. Usually anomalous blue, purple, Moderate Often with Muscovite / Also as alteration product (often of biotite) Perfect Inclined 0-10° Hexagonal / Plates Small Positive or Negative Low-grade Metamorphic Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass Sheet Monoclinic
Chlorite (Fe2+) Dark Olive Green to Brown-Green / Pleochroic Very High / May be Anomalous Blue Moderate to High Length Slow Perfect Straight (Parallel to Cleavage) Thin to Thick Plates / Flaky / Scaly / Fibrous Small 0-30° Negative Metamorphic (Low grade and Blueschist facies) Epidote Glaucophane Lawsonite Pumpellyite Orthochlorite Chlorite Monoclinic
Chlorite (Mg, Fe2+) Pale Green / Weakly Pleochroic Very High / May be Anomalous Blue or Brown Moderate Perfect Straight (Parallel to Cleavage) Thin to Thick Plates / Flaky / Scaly / Fibrous Small to Moderate 0-10° (if Positive) / 0-40° (if Negative) Positive / Negative Igneous (Amygdules in magmatic rocks) Orthochlorite Chlorite Monoclinic
Chlorite (Mg) Colourless / Greenish / Weakly Pleochroic Very High / May be Anomalous Blue Very High to Moderate Anomalous birefringence for Pennine, normal for Clinochlore Perfect Straight (Parallel to Cleavage) Thin to Thick Plates / Flaky / Scaly / Fibrous Small 0-30° (if Positive) / 0-5° (if Negative) Positive / Negative Igneous (Ultrabasic rocks, palaeo-rhyolites and acidic plutonic rocks) Almandine Biotite K-Feldspar Muscovite Plagioclase Quartz Staurolite Orthochlorite Chlorite Monoclinic
Chloritoid Colourless / Green or Gray Blue Pleochroic Low High Cleavage not as good as Mica / Twinning / Hourglass texture Perfect. 2 sets Almost Straight Prisms / Euhedral / Spherical Moderate 36-70° Positive Metamorphic (Low Grade) Albite Glaucophane Jadeite Pumpellyite Garnet Monoclinic / Triclinic
Chromite Reddish / Deep Brown / almost Opaque Isotropic if translucent Very High Simple Twinning None Isotropic Cubes / Octahedral / Small grains Isotropic Isotropic Igneous (Mafic and Ultramafic) Clinopyroxenes Melanite Nepheline Olivine Sodalites Volcanic Glass / Never With Quartz Oxide / Spinel Cubic
Chrysotile / White Asbestos Colourless to Pale Green / Weakly Pleochroic Very Low Low to Very High Asbestos forming in fractures Straight Fibrous / Radiating Small to Large 10-90° (if Positive) / 30-35° (if Negative) Positive / Negative Metamorphic (Hydrothermally altered ultrabasic and basic rocks and Greenschist Facies) Bornite Chalcopyrite Galena Ilmenite Pentlandite Pyrite Pyrrhotite Sphalerite Serpentine Monoclinic
Clinozoisite Colourless Low to Moderate. 0.004-0.015 Anomalous Moderate Anomalous steel-blue birefringence Good Straight parallel to side / Inclined to cleavage Prisms Moderate to Large 40-90° Positive Metamorphic (Low to High grade regional metamorphism, Contact Metamorphism, Blueschist) Biotite Hornblende MuscoviteK-Feldspar Plagioclase Quartz Epidote Monoclinic
Cordierite Colourless Low. 0.008 up to White Low Often Spongy, Porous / may alter to yellow Pinite along cracks and margins / Twinning / Yellow pleochroic haloes around radioactive inclusions / Inclusions of Biotite and Quartz or Graphite in metamorphic rocks Poor Straight Irregular / Hexagonal / Spongy Moderate to Large 35-80° Negative Metamorphic (Low-P metapelites) / rare in igneous Albite Almandine Biotite Quartz Chlorite Kyanite MicroclineK-Feldspar Plagioclase Quartz Staurolite Ring Silicate Orthorhombic
Corundum Colourless to Reddish or Blue / Pleochroic Low (up to 1st order Yellow) High May have zoned colour distribution with pleochroism / Lamellar Twinning / Length Fast Good. 2 sets at 94° Straight Plates / Hexagonal / Needles / Prisms Uniaxial Negative Metamorphic (Al-rich and silica-poor contact metamorphism, regional Schists) Aegirine-Augite Apatite Leucite Melanite Melilite Olivine Sodalites Titanaugite / Never With Quartz Trigonal
Cristobalite Colourless Very Low to Low Very Low Lamellar Twinning / Occurs in cavities in Si-oversaturated igneous rocks / Devitrification product in high T metamorphic rocks (Sanidine facies) Straight Plates / Spherulitic / Needles / Chalcedony-Like /Tabular Prisms / Fibrous Uniaxial or Biaxial Small 2V (25°) Uniaxial Positive / Biaxial Negative Igneous (Fractures of acidic to intermediate Volcanic rocks) / Metamorphic (Sanidinite facies Contact metamorphism) Clinopyroxenes Leucite Melanite Nepheline Olivine Plagioclase Volcanic Glass Sanidine Titanaugite Framework SiO2 Pseudo Cubic
Crossite Pale Yellow / Purple / Blue / Pleochroic Moderate. 0.02 Moderate May be zoned Good. 2 sets at 124° Inclined 5-10° Prisms / Fibrous Small to Moderate 0-50° Negative Metamorphic (Glaucophane Schist, Eclogite) Chromite Clino And Orthopyroxenes Plagioclase Serpentine Alkali Amphibole Monoclinic
Cummingtonite Colourless to Pale Brown Moderate to High. 0.02-0.045 Moderate to High Lamellar Twinning Good. 2 sets at 124° (Amphibole Cleavage) Inclined 10-20° Prisms Moderate to Large 60-85° Positive or Negative Metamorphic / rare in igneous Rutile Garnet Kyanite Zoisite Amphibole Monoclinic
Diopside Colourless / Pale Brownish / Greenish Moderate to High. up to upper 2nd order High Rare Simple Twinning / Exsolution Lamellae in Orthopyroxene / Alters to Amphibole and Serpentine Good. 2 sets at 90° Inclined 35-50° Prisms Moderate 50-70° Positive Igenous (Basic rocks, Kimberlites) / Metamorphic (Marbles, High grade metabasite) Biotite Hornblende Microcline Plagioclase Quartz Sericite Sphene Clinopyroxene Monoclinic
Dolomite Colourless / Brown tinged Very High. 0.179 Low to High Lamellar Twinning / Commonly iron-oxide dusted / Coarser Lamellae than Calcite / Length Fast Perfect Inclined to Cleavage Prisms Uniaxial Negative Metamorphic / Sedimentary Carbonate Trigonal
Enstatite Colourless / Weakly Pleochroic Very Low Moderate to High Zoning with Mg-rich core in Colcanic rocks / often with exsolution lamellae in Plutonic rocks / Alters to serpentine Good. 2 sets Straight Short Columns / Elongate Prisms / Granular Moderate to Large 54-83° Positive Igneous (Basic to ultrabasic rocks) Orthopyroxene Orthorhombic
Epidote Colourless, Yellow or Greenish / Pleochroic Yellow Orange to Red Purple Moderate to High. 0.015-0.05 up to 3rd order / May be Anomalous High Occurs as accessory mineral in granitic rocks Good Straight or Inclined Prisms / Granular / Hexagonal / Radiating Moderate Large 60-90° Positive or Negative Metamorphic (Low-Grade metabasalts, Blueschist, Contact Metamorphism) Leucite Magnetite Melilite Nepheline Sodalites / Never Ilmenite Epidote Monoclinic
Epistilbite Colourless Very Low Very Low High birefringence compared to other zeolites / Simple Twinning / Length Slow Inclined 10° Radial / Fibrous Aggregates / Laths Moderate to Small 44° Positive Metamorphic (Hydrothermal Amygdules in Basalts and Andesites) Albite Almandine Biotite Quartz Chlorite Kyanite MicroclineK-Feldspar Plagioclase Quartz Staurolite Flaky Zeolite Monoclinic
Fluorite Colourless / Blueish / Purple Isotropic Very High Negative Often purple due to radiation damage / Occurs as cement in sandstones / Zonal growth rings / Mottled colour texture / Found in Hydrothermal veins Perfect. 3 sets at 60°/ 2 Sets at 70 Isotropic Cubes / Octahedral / Typically Massive Isotropic Isotropic Igenous / Sedimentary Calcite Diopside Leucite Melilite Nepheline Olivine Pyrope Fluorite Cubic
Garnet Group Colourless to Pale Pink (most common) Isotropic High May be zoned / May have trails with Quartz and Biotite inclusions, which may have S or Z shapes / May alter to chlorite None Isotropic Hexagonal / Octogonal Isotropic Isotropic Metamorphic / rare in igneous Garnet Cubic
Gedrite Colourless Low to Moderate. 0.013 Moderate Good. 2 sets at 124° (Amphibole Cleavage) Straight Prisms Large Positive Metamorphic Clinopyroxenes Leucite Nepheline Olivine Plagioclase Sodalites Amphibole Orthorhombic
Gehlenite Colourless / Yellow / Weakly Pleochroic Low / May be anomalous Purple Blue Moderate Interpenetrating twinning / Length Slow Poor. 2 sets Straight Short Prisms / Granular Uniaxial Negative Igneous (Silica-undersaturated Volcanic rocks) / Metamorphic Biotite Clinopyroxene Olivine Hornblende MicroclineK-Feldspar Orthopyroxene Quartz Titanaugite Volcanic Glass Melilite Tetragonal
Glauconite Green / Pleochroic Very High Moderate Never as oolite (as opposed to chamosite) / Length Slow Pefect Inclined 2-3° Spheres / Elliptic Small 0-20° Negative Metmorphic (Marbles) / Sedimentary (Sandstones) Monoclinic
Glaucophane Pale Yellow / Purple / Blue / Pleochroic Moderate. 0.02 up to Low 2nd order Moderate May be zoned / Length Slow Good. 2 sets at 124° Inclined 5° Prisms / Fibrous Small to Moderate 0-50° Negative Metamorphic (High P Low T) Albite Biotite Hornblende K-Feldspar Microcline Plagioclase Sphene Volcanic Glass Alkali Amphibole Monoclinic
Goethite Yellow / Orange Brown / Pleochroic Very High Very High Component of Limonite Good Straight Needles / Radial Fibrous / Oolitic spheres Small Negative Igneous / Metamorphic (in weathered and altered Fe-minerals and rocks, Cavity and Fracture Filling, Fe-ore deposits) Aegirine-Augite K-Feldspar Anorthoclase Nepheline Riebeckite Sodalite Oxide Orthorhombic
Graphite Greenish Gray / Opaque Very Low to Very High Smeared margins / Often in Barrovian foliated rocks (e.g. Phyllite or Gneisses) Perfect Flakes / Grains Metamorphic Biotite Cordierite Corundum Kyanite Quartz Spinel Hexagonal
Grossularite Colourless / Green to Yellow Isotropic (may be anomalous) High Zonal growth rings / Mottled colour texture None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Metamorphic (e.g. Marbles) / Sedimentary (e.g. Limestones) Biotite Clinopyroxenes Hornblende Orthopyroxenes Plagioclase Quartz Garnet Cubic
Grünerite Colourless to Pale Brown Moderate to High. 0.02-0.045 Moderate to High Lamellar Twinning Good. 2 sets at 124° (Amphibole Cleavage) Inclined 10-20° Prisms Moderate to Large 60-85° Positive or Negative Metamorphic / rare in igneous Amphibole Monoclinic
Gypsum Colourless Very Low Very Low to Low Tends to be distorted / Polysynthetic twinning can form during thin-section making / Simple Twinning Good. 3 sets Inclined 15° Plates / Fibrous / Granular Moderate to Small 58° Positive Sedimentary Monoclinic
Harmotome Colourless Very Low Very Low Heating during thin-section making changes the optical characteristics Inclined 28-32° Thick Columns / Elongate Prisms Large to Small 79° Positive Igneous (Cavity and Fractures Filling in basic Volcanic rocks, in veins in plutonic rocks) Cubic Zeolite Monoclinic
Hastingsite Group Bright Green to Yellow Green / Pleochroic Very Low Moderate to High May have pleochroic haloes / Use associated minerals to distinguish from other amphiboles / Alters to Actinolite, Antigorite, Chlorite / Length Slow Inclined 14-20° Short to Long Columns / Needles / Elongate Prisms Moderate to Large 34-90° Negative Igneous (Intermediate to acidic rocks and Lamprophyrs) / Metamorphic (Amphibolite and Amphibole Schists) Andalusite Biotite Cordierite K-Feldspar Kyanite Muscovite Plagioclase Quartz Green Hornblende Amphibole Monoclinic
Haüyne Colourless / Blue / Purple Blue / Blue Green Isotropic Moderate Negative Dark rims, opaque streaks and clusters / Zoned / Irregular colour distribution / Locally as fine-grained inclusions Good Isotropic Hexagonal / Cubes / Anhedral / Corroded crystals / Isotropic Isotropic Igneous (Mainly alkaline volcanic, rarely plutonic) Leucite Nepheline Sodalite (Feldspathoid) Cubic
Hematite Blood Red / Opaque Not detectable Very High Normally Opaque / Grains may be deep Red on thin edges / Mainly in schists or as accessory mineral in other rocks. None Straight Hexagonal Plates / Granular / Tabular / Fibrous Uniaxial (Opaque) Negative Igneous / Metamorphic (Low to Medium grade) / Sedimentary Clinopyroxenes Leucite Melanite Nepheline Olivine Titanaugite Volcanic Glass / Never With Quartz Oxide Trigonal
Hercynite Deep, "Emerald" Green Isotropic High May be zoned with a darker core / Simple Twinning Isotropic Octahedral / Granular Isotropic Isotropic Igneous (Ultramafic rocks) / Metamorphic (Cordierite Sillimanite Gneisses) Aegirine-Augite Apatite Nepheline K-Feldspar Plagioclase Quartz Sanidine Spinel Cubic
Heulandite Colourless Very Low Very Low Simple Twinning / May occur as Devitrification Product / Length Fast Perfect Inclined 0-32° Platy / Flaky / Radiating / Rosettes / Subparallel Aggregates Small to Moderate 0-50° Positive Igneous (Cavity and Fractures Filling in acidic to basic magmatic rocks) / Metamorphic (in metatuffs and metagreywackes in Zeolite facies) Almandine Cordierite Corundum Flaky Zeolite Monoclinic
Hornblende Green / Brown / Red / orange / Pleochroic Low to Moderate. 0.015-0.02 up to mid 2nd order High Colour of metamorphic Hornblendes often related to grade: Low to high grade goes from Bluish Green to Green to Brownish / Occurs in intermediate Igneous rocks / Occurs in medium grade metamorphic rocks Good. 2 sets at 120° Inclined 2-4° Elongate Prisms / Laths Moderate to Large 50-80° Negative Igneous / Metamorphic (Med grade) Albite Almandine Biotite Kyanite Muscovite Quartz Amphibole Monoclinic
Hypersthene Pale Green / Reddish / Pale Brown / Weakly Pleochroic Very High Moderate to High Outdated term for a mineral in the Enstatite-Ferrosilite series / Zoning with Mg-rich core in Colcanic rocks / often with exsolution lamellae in Plutonic rocks / Alters to serpentine Good. 2 sets Short Columns / Granular / Elongate Prisms Moderate 63-45° Negative Igneous (Intermediate to acidic Volcanic rocks) / Metamorphic (Contact metamorphism, Pyroxene Granulites) Calcite Glaucophane Chlorite Garnet Quartz Sericite Sphene Orthopyroxene Orthorhombic
Illite Colourless High. 0.030-0.035 Low Coats grain surface / Extremely fine Perfect - Fibrous / Wispy / Very fine Small 5-25° Negative Sedimentary Antigorite Actinolite Clinochore Quartz Tremolite Mica Monoclinic
Ilmenite Red in thin flakes or Opaque Not detectable Very High Common accessory mineral None Straight Hexagonal Plates / Laminar / Prismatic / Skeletal / Granular / Flaky Uniaxial (Opaque) Negative Igneous / Metamorphic (High grade) / Sedimentary Apatite Beryl Cassiterite Fluorite Spodumene Topaz Oxide Trigonal
Jadeite Colourless to Pale Green / Weakly Pleochroic Low. 0.006 anomalous Moderate Occurs in Glaucophane rocks and Jadeite-Quartzites Good. 2 sets at 87° Inclined 30-50° / May be Undulose Prisms / Hexagonal / Needles Large 60-90° Positive Metamorphic Albite Epidote Biotite Sphene Talc Calcite Chlorite Quartz Sericite Clinopyroxene Monoclinic
Kaersutite Reddish Brown / Pleochroic Very High Moderate to High May have zoned colour distribution / Hourglass structure / Reaction Rims / Length Slow Inclined 3-19° Short Columns / Elongate Prisms Large 74-82° Negative Igneous (Na-rich basic rocks) Cristobalite Brown Hornblende Amphibole Monoclinic
Kaolinite Colourless / Pale Yellow Low. 0.007 Low Stacks of tiny plates / Often fills pore space / from the alteration of Feldspars Perfect - Plates / Fibrous / Radiating platelets Small to Moderate 25-50° Negative Sedimentary Calcite Diopside Epidote Grossularite Quartz Vesuvianite Clay / Sheet Triclinic / Monoclinic
Katophorite Greenish Brown Very Low Moderate to High May have zoned colour distribution / Hourglass structure / Reaction Rims / Length Slow Inclined 8-16° Small to Moderate 0-57° Negative Igneous (Na-rich Magmatites) Brown Hornblende Amphibole Monoclinic
Koppite Colourless / Red to Brown Isotropic Very High Simple Twinning / Hard to differentiate from Perovskite, Picotite, Cromite and Melanite Isotropic Euhedral (Dodecahedrons; like a Hexagon with more faces) Isotropic Isotropic Igneous (Carbonatites) Apatite Biotite Hornblende Or Nepheline K-Feldspar Quartz Cubic
Kyanite Colourless / Pale Blue Pleochroic Low. 0.012-0.016 up to 1st order Yellow High > Andalusite and Sillimanite Stress induced curving / Length Slow Perfect. 2 sets at 85° Inclined 0-30°max Prisms Large 85° Negative Metamorphic (Moderate to high grade metapelites) Actinolite Albite Chlorite Clinozoisite Epidote Prehnite Sericite Al Silicate Triclinic
Labradorite Colourless Low. up to White Low Albite Twinning lengthways / Carlsbad Twinning / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / Often with Clinopyroxene and/or Olivine in Igenous rocks. Perfect and Good. 2 sets at 86° Inclined 28-39° Prisms / Rectangular Laths Large 70-90° Negative Igenous / Metamorphic (High grade) Fluorite K-Feldspar Li-Mica Quartz Rutile Topaz Tourmaline Plagioclase Feldspar Triclinic
Laumontite Colourless Very Low Very Low Extinction angle related to degree of water loss / Length Slow Inclined 8-11° Radial / Columns / Elongate Prisms / Spherulitic Moderate 33-47° Negative Igneous (Cavity and Fractures Filling in acidic to basic magmatic rocks) / Metamorphic (in metatuffs and metagreywackes in Zeolite facies) Zircon Cassiterite Ilmenite Rutile Mordenite Fibrous Zeolite Monoclinic
Lawsonite Colourless / Rare Blueish Moderate. 0.020 Moderate Lamellar Twinning / Length Fast / in Glaucophane schists, Greenschist and amphibolites Perfect. 2 sets Straight / May be Undulose Diamond / Prisms / Plates Large 76-87° Positive Metamorphic Leucite Nepheline Olivine Perovskite Pyroxene Never With Quartz Epidote Orthorhombic
Lepidolite Colourless / Pale pink / Weakly Pleochroic Very High Very Low to Moderate Pleochroic haloes around zircon / Occurs as fine-speckled in extinction orientation / Length Slow Perfect Straight (Parallel to Cleavage) Platy / Flaky / Scaly / Columns Small to Moderate 23-58° Negative Igneous (Li-rich Granite Pegmatites) / Metamorphic (Greisen) Leucite Nepheline Olivine Perovskite Pyroxene Never With Quartz Lithionite Series Mica Monoclinic
Leucite Colourless Very Low. Almost Isotropic. 0.001 / Anomalous Moderate Negative Multiple Twinning / Volcanic only Poor Straight Euhedral (Icositetrahedral) / Trapeze shaped Almost Isotropic Positive Igneous Opal Zeolites Feldspathoid Tetragonal / Pseudo Cubic
Limonite Ochre-Yellow to Reddish-Brown Very Low / Opaque if dendritic Very High to Very Low Broad term for unidentifiable massive Fe oxides / No visible crystals / Most commonly just Goethite None Oolitic spheres / Crust and Soil-Like / Radiating From alteration of Hematite or Magnetite / Igneous / Metamorphic / Sedimentary Cristobalite Tridymite Volcanic Glass Oxide -
Lizardite Colourless to Pale Green / Weakly Pleochroic Very Low Low Main phase in Bastite (Pseudomorphous after orthopyroxenes) / Length Slow Perfect Straight Fine-Scaly / Fibrous Small 0° Negative Metamorphic (Serpentinites) Analcite Calcite Zeolites Serpentine Monoclinic
Magnesite Colourless / Gray Brown Very High Very Low to High May have Lamellar Twinning / Length Fast Straight Granular / Fibrous / Dense Uniaxial Negative Metamorphic (Talc and chlorite schist, as gel in serpentinites, as ore deposit in metasomatic zones) Carbonate Trigonal
Magnetite Opaque Isotropic if translucent Very High Magnetic / AKA Lodestone None Isotropic Cubes / Octahedral / Granular / Skeletal Isotropic Isotropic Igneous / Metamorphic / Sedimentary Oxide Cubic
Melanite Brown Isotropic Very High Zonal texture None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Igneous (Alkaline rocks) Garnet Cubic
Mesolite Colourless Very Low Very Low Isotypic (Similar crystal structure and chemical formula) with Natrolite and Scolecite / Length Fast Inclined 2-5° Fibrous Large to Small 80° Positive Igneous (Cavity filling in phonolites and basalts) Natrolite Fibrous Zeolite Monoclinic
Microcline Colourless Low. 0.006-0.010 up to Gray Very Low Cross-hatch Twinning Perfect. 2 sets Inclined Prisms Moderate to Large 60-80° Negative Igneous / Metamorphic (Med to High Grade) / Sedimentary Calcite Epidote Fassaite Grossularite Sphene Spinel Wollastonite Alkali Feldspar Triclinic
Monazite Colourless / Green - Yellow / Weakly pleochroic High to Very High High Simple Twinning / May be fractured / May look like Zircon or Sphene / Higher birefringence and less pleochroic than Staurolite Good Straight / May be Inclined 2-6° Tabular / Plates Small 10-25° Positive Igneous (Granites) / Metamorphic (Dolostones and Mica Schists) / Sedimentary (highly resistant to weathering) Epidote Cordierite Apatite Ilmenite Bastnasite Phosphate Monoclinic
Mordenite Colourless / Red Very Low Very Low May occur as Devitrification Product Good Straight Fibrous / Radial / Fine grained Large 76-90° Positive / Negative Igneous (Cavity and Fractures Filling in acidic Volcanic rocks) / Sedimentary Cassiterite Li-Mica Quartz Topaz Tourmaline Mordenite Fibrous Zeolite Orthorhombic
Muscovite Colourless / Pale Yellow / Pale Green (Cr-rich) High. 0.036-0.04 up to upper 2nd order Moderate Cleavage kink due to deformation / Length Slow Perfect Straight or 1-2° (Undulose) Plates / Fine aggregates / Flakes Moderate 30-50° Negative Igneous (Al-rich granites) / Metamorphic / Sedimentary Calcite Zeolite Mica Monoclinic
Natrolite Colourless Very Low Very Low Pseudomorphous after Plagioclases / Length Slow Good Straight Radiating Needles / Lath / Fibrous / Radiating Aggregates Moderate 58-64° Positive Igneous (Cavity filling in basic to intermediate magmatic rocks) Clinopyroxenes Olivine Plagioclase Spinel Natrolite Fibrous Zeolite Orthorhombic
Nepheline Colourless / Cloudy from inclusions Low. 0.009-0.005 (<quartz) up to dark Gray Low Negative Euhedral blocky shapes (i.e. hexagons or rectangles) are only seen in lavas, Anhedral elsewhere / Length Fast Poor Straight Hexagonal / Prisms / Euhedral blocks Uniaxial Negative Igneous (Alkali rocks) Clinopyroxenes Olivine Plagioclase Spinel Feldspathoid Hexagonal
Nosean Colourless Isotropic Moderate Negative Dark rims, opaque streaks and clusters / Zoned / Irregular colour distribution / Locally as fine-grained inclusions Poor Isotropic Hexagonal / Cubes / Anhedral corroded crystals / Isotropic Isotropic Igneous (Mainly alkaline volcanic, rarely plutonic) Biotite Clinopyroxenes Hornblende Plagioclase Volcanic Glass Sodalite (Feldspathoid) Cubic
Oligoclase Colourless Low. up to White Very Low Albite Twinning lengthways / Carlsbad Twinning / Often zoned: typically Anorthite (Na-rich) centres and Albite (Ca-rich) rims. Anorthite cores tend to alter to a fine-grained, turbid, white mica (Sericite) / Often with Biotite and K-feldspar in Igneous rocks / In low-med grade metamorphic rocks Perfect and Good. 2 sets at 86° Inclined 12° Prisms / Rectangular Laths Large 70-90° Negative Igenous / Metamorphic (Low grade) Clinopyroxenes Leucite Nepheline Olivine Plagioclase Sodalites Plagioclase Feldspar Triclinic
Olivine Group Colourless (Mg-rich) to Yellow or Pale Brown (Fe-rich) High. 0.032-0.05 up to upper 2nd order, or 3st in Fayalite (Fe-rich Olivines) High May have different birefringence colours along curving cracks / May alter to serpentine / Occurs in basic and ultrabasic igneous rocks / Occurs in meta marbles / Fayalite (Fe-rich olivines) rare in granitic and syenitic rocks. None. Curving Cracks Straight Diamond / Hexagonal / Octahedral / Granular Uniaxial Positive for Forsterite (Mg-rich) / Negative for Fayalite (Fe-rich) Igneous (Basic to Ultrabasic) / Metamorphic (e.g. Serpentinites, Marbles) Biotite Garnet MicroclineK-Feldspar Plagioclase Pyroxene Quartz Sphene Olivine Orthorhombic
Omphacite Colourless to Pale Green / faintly Pleochroic Low. 0.012 moderately anomalous Moderate to High Like Augite but with lower Birefringence Good . 2 sets at 87° Inclined 34-48° Prisms / Hexagonal Moderate to Large 55-85° Positive Metamorphic (Only Eclogites) Biotite Garnet MicroclineK-Feldspar Plagioclase Pyroxene Quartz Sphene Clinopyroxene Monoclinic
Opal Colourless / Yellowish / Reddish Anomalous Very Low Often altered to Cristobalite or Chalcedony / Shrinkage cracks / Hydrated SiO2 Not a crystal Amorphous / Spherical Not a crystal Not a crystal Igneous (Volcanic) Albite Almandine Epidote Oxide
Orthoclase / K-Feldspar Colourless Low. 0.006-0.010 up to Gray Low Carlsbad Twinning / Perthitic Exsolution common / Often turbid Perfect. 2sets at 90° Straight Prisms Large 60-80° Negative Igneous (Acid to Intermediate rocks, Volcanic) / Metamorphic (Orthogneiss) Biotite Clinopyroxene Orthopyroxene Plagioclase Volcanic Glass Alkali Feldspar Monoclinic
Orthopyroxene Group Colourless to Pale Pink / Green Pleochroic Low. 0.007 to Moderate at Ferrosilite (Fe-rich). up to 1st order Yellow Moderate to High Pleochroic grains usually have a negative optic sign / Occurs in basic and ultrabasic rocks / Occurs in high-grade metamorphic rocks (i.e. metabasites) / Length Fast Good. 2 sets at 87° Straight Prisms / Hexagonal Moderate to Large 55-90° Positive for 88-100 Fe% / Negative at 12-88 Fe% Igneous / Metamorphic Olivine Plagioclase Titanaugite Pyroxene Orthorhombic
Oxybiotite Red to Dark Brown Very Low Moderate to High Reaction Rims / Pleochroic haloes around Zircon / Occurs as fine-speckled in extinction orientation / Length Slow Perfect Straight (Parallel to Cleavage) Platy / Flaky / Scaly / Columns Small 20-30° Negative Igneous (Intermediate Volcanic rocks) Aegirine-Augite Apatite Arfvedsonite Nepheline Sanidine Olivine Titanbiotite Mica Monoclinic
Oxyhornblende Red to Dark Brown Very Low Moderate to High Changeable relief and birefringence in a single crystal / Haloes / Reaction Rims / Length Slow Perfect. 2 sets at 124° Straight to Inclined 12° Short to Long Columns Moderate to Large 56-88° Negative Igneous (Acidic to intermediate Volcanic rocks) Aegirine-Augite Anorthoclase K-Feldspar Nepheline Riebeckite Sodalite Brown Hornblende Amphibole Monoclinic
Paragonite Colourless High. 0.036-0.04 Moderate Perfect Straight or 1-2° (Undulose) Plates Moderate 40° Negative Metamorphic / Sedimentary Beryl Cassiterite Quartz Spodumene Topaz Tourmaline Mica Monoclinic
Perovskite Colourless / Dark Brown / Yellowish / Greenish Isotropic / Very weak / Anomalous Very High May have zoned colour distribution / Very small grains are opaque / Simple and Lamellar Twinning Poor Almost Isotropic Octahedral / Cubes Almost Isotropic Positive Igneous (Kimberlites, Alkaline and Volcanic rocks) Cassiterite Quartz Topaz Wolframite Pervoskite Orthorhombic
Phengite Colourless / Pale Green High. 0.036-0.04 Moderate A Si-rich Muscovite / Can't be distinguished from Muscovite Optically / Length Slow Perfect Straight or 1-2° (Undulose) Fine aggregates / Flakes Moderate 25-35° Negative Igneous / Metamorphic (Glaucophane schist, Eclogite, Gneiss) Clino And Orthopyroxenes Oxyhornblende Plagioclase Quartz Volcanic Glass Sanidine Mica Monoclinic
Phillipsite Colourless Very Low Very Low Interpenetrating Twinning / Occurs in basalt cavities / Length Slow Inclined 11-30° Thick Columns Moderate to Large 60-80° Positive Igneous (Cavity and Fractures Filling in basic Volcanic rocks, Nepheline syenite) Aegirine-Augite Apatite Na-Sanidine Nepheline Nosean Cubic Zeolite Monoclinic
Phlogopite Colourless / Pale Yellow and Green / Orange / Pink / Brown High. 0.028-0.045 Low to Moderate A Mg-rich Mica / Pleochroic Haloes around inclusions / Length Slow Perfect Straight or slightly Inclined Needles / Elongate Laths / Micaceous Flakes Small <15° Negative Igneous (Basic and Ultrabasic, Kimberlites) / Metamorphic (Marbles) Calcite Pyrite Quartz Biotite Mica Monoclinic
Picotite Yellow to Brown Isotropic Very High to Very Low Occurs as small inclusions in Olivines or Serpentine / Simple Twinning Isotropic Granular within Olivine or Serpentine Isotropic Isotropic Igneous (Alkali basalts) Calcite Chlorite Chrysotile Olivine Pyroxene Zeolite Spinel Cubic
Piemontite Yellow / Pink / Magenta / Deep Brown Pleochroism Low to High. 0.025-0.075 / May be Anomalous High A Mn-rich Epidote Good. 2 sets Straight or Inclined Prisms Moderate to Large 50-85° Positive Metamorphic Hornblende Microcline OlivineK-Feldspar Pyroxene Quartz Serpentine Epidote Monoclinic
Pigeonite Colourless to Greenish Pinkish or Brownish Moderate to High. 0.023-0.029 Moderate to High May alter along cracks / Lamellar Twinning / Often as matrix Good. 2 sets at 87° Inclined 37-44° Prisms / Hexagonal Small 0-30° Positive Igneous (Ti-rich Alkali Rocks) Amphibole Biotite Delessite Pyroxene Clinopyroxene Monoclinic
Plagioclase Group Colourless Very Low. 0.007-0.013 Low Lamellar Twinning Perfect Inclined Prisms Large Positive for Ab 77, Negative for An 78 Igneous / Metamorphic / Sedimentary Actinolite Albite Biotite Epidote Glaucophane Lawsonite Pumpellyite Quartz Sericite Zoisite Plagioclase Feldspar Triclinic
Pleonaste Greenish Gray Isotropic High to Very Low Simple Twinning Isotropic Octahedral Isotropic Isotropic Igneous (Mafic) / Metamorphic (e.g. Marbles) Chrysotile Magnesite Olivine Orthopyroxene Talc Spinel Cubic
Prehnite Colourless Very Low / May be Anomalous Blue to Brown Moderate Lamellar Twinning Good Straight Plates / Flaky / Radiating Aggregates / Dendritic / Skeletal Moderate to Large 64-71° Positive Igneous (Basic Volcanic rocks) / Metamorphic (Greenschists, metabasalts and in metamorphic siliceous limestones) Alumino-Silicate Orthorhombic
Pumpellyite Colourless / Green / Blue-Gray / Brownish / Pleochroic Low to Moderate / May be anomalous Blue to Brown Moderate to High Twinning / Zoned / Intergrown with Lawsonite Good. 2 sets Inclined 5-22° Radiating Rays / Laths / Needles / Fibrous / Rosettes Small to Large 7-110° Positive or Negative Metamorphic (Green and Blueschist) Antigorite Bronzite Chrysotile Pumpellyite Epidote Monoclinic
Pyrite Opaque Isotropic High Hard to ID in Transmitted light / Often weathered / Interpenetrating Twinning Isotropic Octahedral / Cubes / Granular Isotropic Isotropic Igneous / Metamorphic (Schists) / Sedimentary Aegirine-Augite Aenigmatite Arfvedsonite Quartz Volcanic Glass Cubic
Pyrochlore Reddish to Opaque Brown Isotropic Very High Simple Twinning / Hard to differentiate from Perovskite, Picotite, Chromite and Melanite Isotropic Octahedral / Granular Isotropic Isotropic Igneous (Pegmatites and Volcanic ejections) Analcite Calcite Heulandite Laumontite Na-Sanidine Nepheline Scolecite Stilbite Thomsonite Cubic
Pyrope Pale Red Isotropic Very Low Celyphytic rims common None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Metamorphic (Peridotites, Kimberlites, Serpentinites and Eclogites) Calcite Chalcedony Zeolite Garnet Cubic
Pyrrhotite Opaque Very Low Hard to ID in Transmitted light Granular / Tabular/ Massive Igneous (Mafic to Ultramafic) Albite Analcite Calcite Chabazite Chalcedony Chlorite Heulandite Natrolite Scolecite Stilbite Thomsonite Hexagonal
Quartz Colourless Low. 0.009 up to cream Low Length Slow None Straight if Prisms edge visible (may be Undulose) Irregular Prisms Uniaxial Positive Igneous / Metamorphic (Low grade) / Sedimentary Albite Analcite Calcite Chabazite Chalcedony Chlorite Heulandite Natrolite Scolecite Stilbite Thomsonite Framework SiO2 Trigonal
Riebeckite Green / Purple / Brown / Dark Blue / Pleochroic Low. 0.006-0.016 / May be anomalous Moderate to High Length Fast Good. 2 sets at 124° Inclined 3-15° Short Prisms / Needles Moderate to Large 40-100° Negative to Positive Igneous (Na-rch) / Metamorphic Heulandite Laumontite Stilbite Alkali Amphibole Monoclinic
Rutile Deep Reddish Brown / Yellow Brown / Opaque Very High. 0.29 Very High Occurs in coarse-grained, high pressure, metamorphic rocks (e.g. eclogites, or kyanite-bearing) / Occurs in Igneous rocks as tiny grains (may be opaque) / May have radioactive haloes / Length Slow Good Straight (Not easy to see) Granules / Plates Uniaxial Positive Metamorphic (High-P) / Igneous Albite Apophyllite Calcite Chlorite Epidote Prehnite Quartz Zeolite Oxide Tetragonal
Sanidine Colourless Low. 0.006-0.008 Low Small 2V is key / Carlsbad Twinning Perfect Straight Prisms Small to Moderate 0-60° Negative Igneous Analcite Laumontite Quartz Stilbite Alkali Feldspar Monoclinic
Sapphirine Colourless / Pale Blue Pleochroic Very Low to Low. 0.005-0.009 anomalous High Often in Symplectite associations Moderate Straight or slightly Inclined Irregular Moderate to Large Negative Metamorphic Calcite Clay Minerals Heulandite Laumontite Quartz Pyroxene Monoclinic
Scapolite Group Colourless / Yellow Very Low (Na) to High (Ca) Low to Moderate May be cloudy / Fluid and mineral inclusions common / Scapolite group is a series between Marialite and Meionite Good. 2 sets Straight or symmetrical to cleavage Cubes / Prisms Uniaxial Negative Igneous / Metamorphic Chabazite Heulandite Laumontite Mordenite Scolecite Stilbite Framework Tetragonal
Scolecite Colourless Very Low Very Low Simple Twinning / Length Fast Good Inclined 15-18° Fibrous / Radial Moderate 36-58° Negative Igneous (Amygdules in basic to ultramafic magmatic rocks) / Metamorphic (Fracture filling) Analcite Calcite Chabazite Chalcedony Natrolite Thomsonite Natrolite Fibrous Zeolite Monoclinic
Sericite Colourless Moderate to High Low to Moderate From the hydrothermal alteration of Orthoclase or Plagioclase / Variety of Muscovite Good Straight Flakes / Irregular Granules Moderate 30-50° Negative Metamorphic Feldspars Biotite Muscovite Ore Deposits Tin Copper Quartz Pyrite Fluorite Epidote Calcite Mica Monoclinic
Serpentine Group Colourless Low. 0.006-0.013 Low Positive Mineral group with Lizardite, Chrysotile, Antigorite/ Mesh window texture / From the alteration of Olivine Good Straight Fibrous / Flakes Uniaxial or Moderate Negative Igneous / Metamorphic Calcite Hyalophane Laumontite Natrolite Sheet Trigonal / Monoclinic / Orthorhombic
Siderite Colourless to Pale Yellow Brown Very High Moderate to Very High Carbonates with the highest relief and birefringence / Simple Twinning / Length Fast Straight Granular / Oolitic spheres / Needles / Dendritic Aggregates / Skeletal Uniaxial Negative Metamorphic (as gangue in ore body, as ore in metasomatic and hydrothermal deposits) Analcite Calcite Phillipsite Thomsonite Carbonate Trigonal
Sillimanite Colourless / Rare Brown Moderate. 0.018-0.022 up to mid 2nd order. High Higher briefringence and relief than Andalusite / Fibrous texture often associated with Biotite / Needles often associated with Quartz / Length Slow Good Straight Fibrous (Fibrolite) or Diamond/ Needles Small 20-30° Positive High T Metamorphic Aegirine-Augite Anorthoclase Arfvedsonite Riebeckite Al Silicate Orthorhombic
Smectite Group Colourless / Pale Brown / Yellow / Olive-Green Moderate to High Low Group of Clay minerals / Fills pores / Main constituent of Bentonite Perfect - Irregular Plates - Negative Sedimentary Beryl Cassiterite Wolframite Fluorite Li-Mica Quartz Tourmaline Clay / Sheet Monoclinic
Sodalite Colourless / Pale Gray Isotropic Moderate Negative Simple Twinning / Slight birefringence around inclusions Poor Isotropic Anhedral to Euhedral / Cubes / Hexagonal / Corroded-looking Isotropic Isotropic Igneous (Mainly alkaline volcanic) Calcite Gypsum Halite Quartz Sodalite (Feldspathoid) Cubic
Spessartine Pale Yellow Isotropic High with Almandine None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Metamorphic (Hornfels) / Sedimentary Anhydrite Calcite Halite Quartz Garnet Cubic
Sphene / Titanite Colourless to Pale Brown Very High. 0.1-0.2 Extreme - pinky buff colours Very High Occurs in intermediate and acid igneous rocks / Occurs in metabasites / Low birefringence grains seldom go fully extinct, going from dull anomalous orange to dull blue Good Inclined 35-50° Commonly Diamond / Lozenge shaped Small to Moderate 17-55° Positive Igneous (Intermediate and Acidic, never in Gabbro or Basalts) / Metamorphic (Amphibolites, Marbles) Celestite Quartz Humite Monoclinic
Spinel Group Colourless / Brown / Green / Pink / Pale Blue / Never Pleochroic Isotropic if translucent Very High Simple Twinning / Transparent Spinels mainly in metamorphic rocks / Colourless Spinels in marbles / Coloured Spinels in high-grade metapelites / Deep Brown, Cr-rich, Spinels in basic and ultrabasic rocks None Isotropic Cubes / Octahedral Isotropic Isotropic Metamorphic Hematite Lepidocrocite Oxide / Spinel Cubic
Staurolite Honey Yellow / Pleochroic Low. 0.011-0.014 up to 1st order Yellow High Only found in metapelites / Usually as porphyroblasts with quartz inclusions / Length Slow Moderate Straight Short Prisms / Tabular Large 80-90° Positive Metamorphic (Metapelites) Kyanite Garnet Mica Biotite Sillimanite Staurolite Monoclinic / Orthorhombic
Stilbite Colourless Very Low Very Low Interpenetrating Twinning Inclined 3-12° Radial / Fibrous / Bundled Aggregates / Skeletal / Plates Small to Moderate 30-49° Negative Igneous (Cavity and Fractures Filling in basic to acidic Volcanic rocks) Clinopyroxenes Arfvedsonite K-Feldspar Nepheline Riebeckite Flaky Zeolite Monoclinic
Stilpnomelane Yellow / Green / Brown / Strongly Pleochroic High to Very High. 0.03-0.11 Moderate to High Cleavage less perfect than Biotite / Length Slow Good Straight Elongate Prisms / Laths / Needles / Radiating / Flaky Pseudo Uniaxial Negative Metamorphic (Phyllite, Schist, Quartzite, Blueschist) Biotite Chlorite Hornblende Muscovite Quartz Sheet Triclinic / Monoclinic
Talc Colourless to Pale Green High. 0.037-0.050 Moderate Indisguishable from Sericite by microscope / Very soft clay / From the alteration of Mg Silicates / Length Slow Perfect Straight Fibrous / Scaly Small 0-30° Negative Metamorphic / Sedimentary Clay / Sheet Monoclinic
Thomsonite Colourless Very Low Very Low to Low Highest birefringence of all the Zeolites / May have Simple Twinning / Renamed in 1820 in honour of Scotsman Thomas Thomson, professor of chemistry at the University of Glasgow. Perfect Straight Radially / Fibrous / Columns / Elongate Prism / Flaky Moderate to Large 44-75° Positive Igneous (Amygdules in basic to ultramafic magmatic rocks) / Metamorphic (Fracture filling) Calcite Clay Minerals Quartz Natrolite Fibrous Zeolite Orthorhombic
Titanaugite Brown / Purple / Brownish Yellow / Pleochroic Very High High Hourglass texture / Zoned / Anomalous Brown to Blue-Gray at extinction/ Twinning Good. 2 sets at 87° Inclined 32-55° Short to Long Columns / Platy Moderate 42-65° Positive Igneous (Ti-rich alkali rocks) Alkali-Feldspar Volcanic Glass Tridymite Zeolite Clinopyroxene Monoclinic
Titanbiotite Orange / Red Brown Very Low Moderate to High Weathered grains are bleached / Pleochroic haloes around Zircon / Occurs as fine-speckled in extinction orientation / Length Slow Perfect Straight (Parallel to Cleavage) Platy / Flaky / Scaly / Columns Small to Moderate 5-38° Negative Igneous (Na-rich, Ti-rich magmatic rocks) Chlorite K-Feldspar Mica Plagioclase Quartz Rutile Mica Monoclinic
Topaz Colourless Very High Moderate Contains fluid inclusions / Length Slow / Named after Topasos Island in the Red Sea Perfect Straight Short Columns / Needles / Laths / Granular Moderate 48-68° Positive Metamorphic (Greisen and granitic contact metamorphism) / Igneous (Tin pegmatites) Apatite Calcite Diopside Vesuvianite Wollastonite Quartz Mica Feldspar Fluorite Cassiterite Tourmaline Orthorhombic
Tourmaline Opaque / Blue / Green / Yellow / Brown / Strongly Pleochroic Moderate. 0.02-0.03 up to up 2nd order. Moderate Pleochroism darkest when N-S / Often colour zoned / Radioactive haloes around Zircon / Good indication that the rock is Boron rich / Distinguished from biotite and hornblende by the lack of cleavage / Length Fast Poor Straight Triangular / Prisms / Needle-like Uniaxial Negative Igneous / Metamorphic Topaz Epidote Trigonal
Tremolite Colourless to Green Pleochroic Moderate. 0.027 up to mid 2nd Moderate Colour more intense for Fe-rich Tremolites / Only found in carbonate-rich metamorphic rocks (e.g. marbles) / May have pleochroic haloes / Length Slow Good. 2 sets at 124° Inclined 30° max typically 10-15° Fine Prisms / Laths / Fibrous / Needle-like Large 80-90° Negative Metamorphic (Green and Blueschist, Serpentinite, Marbles) Apatite Calcite Phlogopite Actinolite Amphibole Monoclinic
Tridymite Colourless Very Low. 0.002-0.004 Moderate Negative Lines vesicles in high temperature lavas / High temperature polymorph of Quartz / Occurs in volcanic rocks / Fracture Filling / Twinning / Length Fast Poor Straight Radiating Rays / Platy Moderate to Large 40-90° Positive Igneous (Volcanic) Metamorphic (Sanidine facies contact met.) Framework SiO2 Orthorhombic
Tschermakite Group Bright Green to Yellow Green / Pleochroic Very High Moderate to High May have pleochroic haloes / Use associated minerals to distinguish from other amphiboles / Alters to Actinolite, Antigorite, Chlorite / Length Slow Inclined 15-22° Short to Long Columns / Needles Moderate to Large 65-90° Negative Igneous (Intermediate to acidic rocks and Lamprophyrs) / Metamorphic (Amphibolite and Amphibole Schists) Clinopyroxenes Leucite Nepheline Sanidine Sodalites Green Hornblende Amphibole Monoclinic
Uvarovite Pale "Emerald" Green Isotropic (may be anomalous) Very High Zonal growth rings / Mottled colour texture None Isotropic Euhedral (Rhombic Dodecahedrons; like a Hexagon with more faces) / Anhedral Grains Isotropic Isotropic Found in Chromite rich rocks Tridymite Zeolite Garnet Cubic
Vesuvianite / Idocrase Colourless / Yellow / Green / Brown / Weakly Pleochroic Low / May be anomalous Purple Blue or Leather Brown High May have zoned colour distribution / Hourglass texture Poor Straight Short Prisms / Granular / Needles / Spherulitic Uniaxial Positive / Negative Metamorphic (Contact metamorphism and marbles) Olivine Serpentine Tetragonal
Volcanic Glass Colourless / Yellow to Brown Opaque / Anomalous Very Low to Moderate Fluid textures / Contraction and Conchoidal fractures / Radial devitrification textures Amorphous Igneous (Volcanic rocks, dykes and sills) Carbonates Serpentine - -
Wollastonite Colourless Low. 0.013 Moderate Refractive index < Diopside / Twinning / Poikiloblastic Good. 3 sets at 84 and 70° Inclined 30-40° Prisms / Hexagonal / Needles Moderate 35-60° Negative Metamorphic (Marbles) Technically not a Pyroxene Triclinic
Xenotime Colourless / Yellow / Green / Red / Weakly Pleochroic Very High High May have Pleochroic haloes / Length Slow Good Straight Short Prisms / Granular Uniaxial Positive Igneous (Felsic rocks) / Metamorphic (Orthogneiss) / Sedimentary (Sandstones) Phosphate Tetragonal
Zeolite Group Colourless Low (1st order White) Low to Moderate Negative Cavity filling in volcanic rocks - - - Uniaxial or Biaxial Positive or Negative Igneous Olivine Phlogopite Pyroxene Serpentine Feldspathoid -
Zinnwaldite Colourless to Brown-grey / Weakly Blue Gray Pleochroic Very High Low to Moderate Occurs as fine-speckled in extinction orientation / Length Slow Perfect Straight (Parallel to Cleavage) Fan Shaped / Radiating / Platy / Flaky / Scaly / Columns Small to Moderate 15-32° Negative Igneous (Granite Pegmatites) / Metamorphic (Greisen) Cassiterite Clino And Ortho Pyroxene Ilmenite Magnetite Olivine Plagioclase Lithionite Series Mica Monoclinic
Zircon Colourless to Pale Brown / Greenish or Pink / Weak or No Pleochroism High. 0.04-0.065 up to 3rd order Very High Often within biotite / May have pleochroic haloes / May be zoned / Rich in inclusions / Occurs as rare detrital grains in Quartzites and mature sedimentary rocks / Length Slow Poor Straight Prisms / Cubes / Small Euhedral crystals Uniaxial Positive Igneous (often in nepheline syenites) / Metamorphic / Sedimentary Humite Tetragonal
Zoisite / Thulite Colourless / Purple / Strongly Pleochroic Very Low / Anomalous Blue to Brown Moderate Length Fast Good. 2 sets Straight Prisms Uniaxial Positive Metamorphic (Low Grade) Epidote Orthorhombic