Silicate minerals

▪ Table

Silicate minerals

name colour lustre Mohs hardness specific gravity

Tectosilicates (three-dimensional networks)

feldspar (for other examples, see feldspar)

orthoclase flesh-red, white to pale yellow, red, green vitreous 6–6½ 2.6

feldspathoid (for other examples, see feldspathoid)

nepheline light-coloured; reddish, greenish, brownish vitreous to greasy 5½–6 2.6–2.7

silica (for other examples, see silica mineral)

quartz variable vitreous to greasy (coarse-grained); waxy to dull (fine-grained) 7 (a hardness standard) 2.65

zeolite (for other examples, see zeolite)

chabazite white; flesh-red vitreous 4½ 2.0–2.1

Phyllosilicates (sheet structures)

clay (for other examples, see clay mineral)

chlorite green vitreous or pearly 2–3 2.6–3.0

smectite 2.2–2.7

mica (for other examples, see mica)

apophyllite colourless, white, pink, pale yellow, or green pearly iridescent 4½–5 2.3–2.4

muscovite commonly white or colourless; light shades of green, red, or brown vitreous to silky or pearly 2–2½ 2.8–3.0

prehnite pale green to gray, white, or yellow vitreous 6–6½ 2.9–3.0

pyrophyllite white and various pale colours dull and glistening 1–2 2.6–2.9

talc colourless; white; pale or dark green; brown pearly 1 (a hardness standard) 2.6–2.8

Inosilicates (chain structures)

amphibole (for other examples, see amphibole)

common hornblende pale to dark green glassy 5–6 3.0–3.4

mullite white 3.0

pyroxene (for other examples, see pyroxene)

augite brown, green, black vitreous 5½–6 3.2–3.5

rhodonite pink to brownish red vitreous 5½–6½ 3.6–3.8

wollastonite white; also colourless, gray, or very pale green vitreous 4½–5 2.9–3.1

Cyclosilicates (ring structures)

axinite clove- or lilac-brown; pearl-gray; yellowish highly glassy 6½–7 3.3–3.4

beryl various greens; variable, including deep-green (emerald), blue-green (aquamarine), pink (morganite), yellow (heliodore) vitreous 7½–8 2.7–2.8

cordierite various blues vitreous 7 2.5–2.8

tourmaline extremely variable vitreous to resinous 7–7½ 3.0–3.2

Sorosilicates (double tetrahedral structures)

hemimorphite white, sometimes tinted bluish or greenish; yellow to brown vitreous 5 3.4–3.5

melilite colourless; grayish green; brown vitreous to resinous 5–6

gehlenite 3.1

åkermanite 2.9

Nesosilicates (independent tetrahedral structures)

andalusite pink, white, or rose-red; also variable vitreous 6½–7½ 3.1–3.2

chrysocolla green, bluish green vitreous 2–4 2.0–2.8

datolite colourless or white; also various pale tints vitreous 5–5½ 2.9–3.0

epidote yellowish green to dark green vitreous 6–7 3.3–3.5

garnet variable vitreous to resinous 6–7½

almandine 4.3

andradite 3.9

grossularite 3.6

pyrope 3.6

spessartite 4.2

uvarovite 3.9

kyanite blue; white; also variable vitreous to pearly 4–7 (variable) 3.5–3.7

olivine (for other examples, see olivines)

forsterite-fayalite series various greens and yellows vitreous 6½–7 3.2 (forsterite) to 4.4 (fayalite)

phenacite colourless; also wine-yellow, pale rose, brown vitreous 7½–8 3.0

sillimanite colourless or white; also various browns and greens vitreous to subadamantine 6½–7½ 3.2–3.3

sphene colourless, yellow, green, brown, black adamantine to resinous 5 3.4–3.6

staurolite dark red-brown; yellow-brown; brown-black subvitreous to resinous 7–7½ 3.7–3.8

thorite black; also orange-yellow (orangite) 4½–5 4.5–5.0; 5.2–5.4 (orangite)

topaz straw- or wine-yellow; white; grayish, greenish, bluish, reddish vitreous 8 (a hardness standard) 3.5–3.6

vesuvianite yellow, green, brown vitreous 6–7 3.3–3.4

willemite white or greenish yellow vitreous to resinous 5½ 3.9–4.2

zircon reddish brown, yellow, gray, green, or colourless adamantine 7½ 4.6–4.7

zoisite white; gray; green-brown; pink (thulite) vitreous 6–6½ 3.2–3.4

name habit fracture or cleavage refractive indices crystal system

Tectosilicates (three-dimensional networks)

feldspar (for other examples, see feldspar)

orthoclase twinned crystals two good cleavages of 90 degrees alpha = 1.518–1.529

beta = 1.522–1.533

gamma = 1.522–1.539 monoclinic

feldspathoid (for other examples, see feldspathoid)

nepheline small glassy crystals or grains poor cleavage omega = 1.529–1.546

epsilon = 1.526–1.542 hexagonal

silica (for other examples, see silica mineral)

quartz prismatic and rhombohedral crystals; massive conchoidal fracture omega = 1.544

epsilon = 1.553 hexagonal

zeolite (for other examples, see zeolite)

chabazite single, cubelike rhombohedrons poor cleavage omega = 1.470–1.494

epsilon = 1.470–1.494 hexagonal

Phyllosilicates (sheet structures)

clay (for other examples, see clay mineral)

chlorite large crystalline blocks; fine-grained, flaky aggregates platy cleavage alpha = 1.57–1.64

gamma = 1.575–1.645 monoclinic or triclinic

smectite broad undulating mosaic sheets that break into irregular fluffy masses of minute particles alpha = 1.480–1.590

gamma = 1.515–1.630

mica (for other examples, see mica)

apophyllite tabular, prismatic, or granular crystals; prisms and bipyramids when well-formed one perfect, one poor cleavage omega = 1.534–1.535

epsilon = 1.535–1.537 tetragonal

muscovite large tabular blocks (called books); pseudohexagonal crystals; fine-grained aggregates one perfect, platy cleavage alpha = 1.552–1.574

beta = 1.582–1.610

gamma = 1.587–1.616

prehnite rosettes of small radiating crystals; tabular or prismatic crystals; lamellar or botryoidal massive one good cleavage alpha = 1.611–1.632

beta = 1.615–1.642

gamma = 1.632–1.665 orthorhombic

pyrophyllite lamellar massive; granular to compact massive one perfect cleavage alpha = 1.534–1.556

beta = 1.586–1.589

gamma = 1.596–1.601 monoclinic

talc compact foliated masses one perfect cleavage alpha = 1.539–1.553

beta = 1.589–1.594

gamma = 1.589–1.600 monoclinic

Inosilicates (chain structures)

amphibole (for other examples, see amphibole)

common hornblende massive one good cleavage of 56 degrees alpha = 1.615–1.705

beta = 1.618–1.714

gamma = 1.632–1.730 monoclinic

mullite elongated prismatic crystals; melts one distinct cleavage alpha = 1.642–1.653

beta = 1.644

gamma = 1.654–1.679 orthorhombic

pyroxene (for other examples, see pyroxene)

augite short, thick, tabular crystals one good cleavage of 87 degrees alpha = 1.671–1.735

beta = 1.672–1.741

gamma = 1.703–1.761 monoclinic

rhodonite rounded tabular crystals; cleavable to compact massive; embedded grains two perfect cleavages alpha = 1.711–1.738

beta = 1.715–1.741

gamma = 1.724–1.751 triclinic

wollastonite cleavable, fibrous, or compact massive; tabular crystals one perfect, two good cleavages alpha = 1.616–1.640

beta = 1.628–1.650

gamma = 1.631–1.653 triclinic

Cyclosilicates (ring structures)

axinite broad, sharp-edged, wedge-shaped crystals; lamellar massive one good cleavage alpha = 1.674–1.693

beta = 1.681–1.701

gamma = 1.684–1.704 triclinic

beryl long hexagonal crystals conchoidal to uneven fracture omega = 1.569–1.598

epsilon = 1.565–1.590 hexagonal

cordierite short prismatic crystals; embedded grains; compact massive one distinct cleavage alpha = 1.522–1.558

beta = 1.524–1.574

gamma = 1.527–1.578 orthorhombic

tourmaline parallel or radiating groups of striated, elongated hexagonal prisms, often rounded or barrel-shaped; massive subconchoidal to uneven fracture omega = 1.635–1.675

epsilon = 1.610–1.650 hexagonal

Sorosilicates (double tetrahedral structures)

hemimorphite sheaflike crystal aggregates one perfect cleavage alpha = 1.614

beta = 1.617

gamma = 1.636 orthorhombic

melilite short prismatic crystals; tablets one distinct cleavage tetragonal

gehlenite omega = 1.669

epsilon = 1.658

åkermanite omega = 1.632

epsilon = 1.640

Nesosilicates (independent tetrahedral structures)

andalusite coarse prisms; massive one good cleavage of 89 degrees alpha = 1.629–1.640

beta = 1.633–1.644

gamma = 1.638–1.650 orthorhombic

chrysocolla crusts; botryoidal masses conchoidal fracture omega = 1.46

epsilon = 1.54 orthorhombic?

datolite tabular or short prismatic crystals; botryoidal and globular or divergent and radiating massive conchoidal to uneven fracture alpha = 1.622–1.626

beta = 1.649–1.654

gamma = 1.666–1.670 monoclinic

epidote striated elongated crystals; fibrous or granular massive; disseminated one perfect cleavage alpha = 1.712–1.756

beta = 1.720–1.789

gamma = 1.723–1.829 monoclinic

garnet crystals; irregular embedded grains; compact, granular, or lamellar massive subconchoidal fracture isometric

almandine n = 1.830

andradite n = 1.887

grossularite n = 1.734

pyrope n = 1.714

spessartite n = 1.800

uvarovite n = 1.86

kyanite elongated tabular, bladed crystals one good, one perfect cleavage alpha = 1.712–1.718

beta = 1.719–1.723

gamma = 1.727–1.734 triclinic

olivine (for other examples, see olivines)

forsterite-fayalite series flattened crystals; compact or granular massive; embedded grains one indistinct cleavage alpha = 1.631–1.827

beta = 1.651–1.869

gamma = 1.670–1.879 orthorhombic

phenacite rhombohedral crystals one distinct cleavage omega = 1.654

epsilon = 1.670 hexagonal

sillimanite vertically striated, square prisms; long, slender parallel crystal groups to fibrous or columnar massive one perfect cleavage alpha = 1.654–1.661

beta = 1.658–1.670

gamma = 1.673–1.684 orthorhombic

sphene wedge-shaped crystals, often twinned; compact massive one good cleavage alpha = 1.843–1.950

beta = 1.870–2.034

gamma = 1.943–2.110 monoclinic

staurolite cruciform twins one distinct cleavage alpha = 1.739–1.747

beta = 1.744–1.754

gamma = 1.750–1.762 monoclinic

thorite square prismatic crystals; small masses one distinct cleavage omega = 1.8 tetragonal

topaz prismatic crystals one perfect cleavage alpha = 1.606–1.629

beta = 1.609–1.631

gamma = 1.616–1.638 orthorhombic

vesuvianite prismatic crystals; massive subconchoidal to uneven fracture omega = 1.703–1.752

epsilon = 1.700–1.746 tetragonal

willemite hexagonal prismatic crystals; disseminated grains; fibrous massive one easy cleavage omega = 1.691–1.714

epsilon = 1.719–1.732 hexagonal

zircon square prismatic crystals; irregular forms; grains conchoidal fracture omega = 1.923–1.960

epsilon = 1.968–2.015 tetragonal

zoisite striated prismatic crystals; columnar to compact massive one perfect cleavage alpha = 1.685–1.705

beta = 1.688–1.710

gamma = 1.697–1.725 orthorhombic

See as table:

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