Important gemstones

mineral gem name colour Mohs hardness* specific gravity*

beryl aquamarine sky blue to greenish blue 7½–8 2.68–2.71

emerald green 2.68–2.74

goshenite colourless; greenish yellow, yellow green, brownish same as aquamarine

heliodor golden yellow same as aquamarine

morganite pink 2.80–2.90

chrysoberyl alexandrite; also cymophane; cat's-eye green in daylight, red in incandescent light 8½ 3.6–3.8

corundum padmaradschah orange 9 4.0–4.1

ruby red

sapphire blue; variable other than red

diamond colourless to faint yellowish tinge; also variable 10 3.52

feldspar

potash

feldspar orthoclase pale yellow; flesh red 6 2.6

moonstone colourless; also white to yellowish, and reddish to bluish gray

amazonite (amazon-stone) yellow green to blue green

plagioclase peristerite pastel pink to gray 6–6½ 2.6–2.7

sunstone (aventurine) colourless with reddish glow provided by inclusions

labradorite grayish

garnet

almandine carbuncle deep red with a trace of purple 7½ 4.3

andradite demantoid; Uralian emerald deep emerald-green 6½ 3.9

grossularite hessonite; South African jade brownish yellow or orange to orange, red, or green 7¼ 3.6

pyrope dark blood red 7–7½ 3.6

spessartite yellowish orange; brownish to orange red 7¼ 4.2

jade

jadeite Imperial jade pure white to black, red, brown, yellow, blue, mauve, various greens 6 3.2–3.4

nephrite mutton-fat jade deep spinach green to near-white 5–6 3.0–3.4

lazurite lapis; lapis lazuli deep blue, azure blue, greenish blue 5–5½ 2.4–2.95

(bluish coloured with flecks of white and gold) (5½) (2.7–2.9)

olivine peridot; chrysolite yellow green; dark bottle green; olive green 6½–7 3.3–3.5

silica

quartz amethyst purple 7 2.65

cairngorm; smoky quartz smoky gray to brown

citrine yellow

rock crystal colourless

rose quartz pink

agate (moss agate, mocha stone) variable

chalcedony (onyx carnelian, sard, sardonyx, prase, chrysoprase, plasma, bloodstone, heliotrope) variable

jasper variable

cristobalite opal white to colourless; milky to bluish white; variable pale shades 7 2.0–2.3

spinel Balas ruby rubicelle almandine red; also variable 8 3.6

topaz wine yellow; pale blue, green, violet, or red 8 3.5–3.6

tourmaline achroite colourless 7–7½ 3.0–3.2

Brazilian emerald green

dravite brown

indicolite dark blue

rubellite pink

siberite violet

turquoise sky blue; greenish blue 6 2.6–2.8

zircon jargon variable 7½ 4.6–4.7

Matura diamond colourless

hyacinth (jacinth) yellow, orange, red, brown

mineral gem name refractive indices dispersion* transparency crystal system habit remarks

beryl aquamarine epsilon = 1.570–1.580

omega = 1.574–1.586

d = 0.014 transparent hexagonal large, often flawless, crystals with complex terminations

emerald epsilon = 1.571–1.581

omega = 1.577–1.588 simple hexagonal crystals terminated by a flat face; often contains inclusions

goshenite same as aquamarine

heliodor same as aquamarine

morganite epsilon = 1.580–1.590

omega = 1.589–1.601

chrysoberyl alexandrite; also cymophane; cat's-eye alpha = 1.746

beta = 1.748

gamma = 1.756

d = 0.015 transparent orthorhombic flattened crystals often twinned chrysoberyl cat's-eye is chatoyant

corundum padmaradschah epsilon = 1.757–1.768

omega = 1.765–1.776

d = 0.018 transparent hexagonal

ruby flat-terminated crystals fluoresces in ultraviolet light; marked dichroism

sapphire pointed dipyramids marked diochroism

diamond n = 2.4175

d = 0.063 transparent isometric flattened octahedrons; dodecahedrons perfect cleavage parallel to octahedron face; sometimes fluorescent in long-wave ultraviolet light

feldspar

potash

feldspar orthoclase alpha = 1.518

beta = 1.522

gamma = 1.522 transparent to opaque monoclinic crystals two excellent cleavages at right angles

moonstone same as orthoclase nodules; masses blue opalecsence; schiller

amazonite (amazon-stone) alpha = 1.514

beta = 1.518

gamma = 1.521 triclinic large crystals variety of microcline

plagioclase peristerite alpha = 1.527–1.577

beta = 1.531–1.585

gamma = 1.538–1.590 transparent to opaque triclinic prismatic crystals iridescent

sunstone (aventurine) spangled appearance

labradorite compact masses brilliantly iridescent over large areas

garnet

almandine carbuncle n = 1.830

d = 0.024 transparent (for light-coloured varieties) to opaque isometric euhedral crystals, with dodecahedrons and trapezohedrons most common

andradite demantoid; Uralian emerald n = 1.887

d = 0.057

grossularite hessonite; South African jade n = 1.734

d = 0.028

pyrope n = 1.714

d = 0.027

spessartite n = 1.800

jade

jadeite Imperial jade alpha = 1.640–1.658

beta = 1.645–1.663

gamma = 1.652–1.673 translucent to opaque monoclinic compact or fibrous masses

nephrite mutton-fat jade alpha = 1.600–1.672

beta = 1.614–1.686

gamma = 1.627–1.693 translucent to opaque monoclinic compact or fibrous masses

lazurite lapis; lapis lazuli n = 1.50

(opaque) isometric

(compact masses) lapis lazuli is a rock containing lazurite as its colouring agent; because it is a rock, its composition and properties are variable; properties given in parentheses are for the rock, the others for the mineral lazurite

olivine peridot; chrysolite alpha = 1.635–1.671

beta = 1.652–1.698

gamma = 1.671–1.707

d = 0.020 transparent orthorhombic flattened prismatic crystals; granular masses

silica

quartz amethyst epsilon = 1.553

omega = 1.544

d = 0.013 transparent hexagonal

cairngorm; smoky quartz octahedral crystals

citrine

rock crystal

rose quartz

agate (moss agate, mocha stone) translucent to opaque compact masses; nodules

chalcedony (onyx carnelian, sard, sardonyx, prase, chrysoprase, plasma, bloodstone, heliotrope)

jasper

cristobalite opal n = 1.435–1.455 opaque tetragonal submicrocrystalline aggregates; globular or kidney-like crusts; irregular concretions contains a variable amount of water, causing the physical properties to vary

spinel Balas ruby rubicelle almandine n = 1.715–1.725

d = 0.020 transparent isometric octahedral crystals; rounded grains; massive fluoresces red in long-wave ultraviolet light

topaz alpha = 1.606–1.629

beta = 1.609–1.631

gamma = 1.616–1.638

d = 0.014 transparent orthorhombic prismatic crystals

tourmaline achroite epsilon = 1.610–1.650

omega = 1.635–1.675

d = 0.016 transparent hexagonal prismatic crystals, often rounded or barrel-shaped; massive

Brazilian emerald

dravite

indicolite

rubellite

siberite

turquoise alpha = 1.61

beta = 1.62

gamma = 1.65 opaque triclinic cryptocrystalline to fine granular massive colour fades on contact with sunlight

zircon jargon epsilon = 1.968–2.015

omega = 1.923–1.960

d = 0.048 transparent tetragonal square prismatic crystals; grains

*Properties given here are for gem-quality material and hence may differ from those of the mineral.