Gems

Quartz (Crystalline)

Amber

Chemical CompositionC-H-O compound (fossil resin)
Crystal SystemAmorphous
FractureConchoidal, brittle
Hardness2-2.5
Refractive Index1.54
Specific Gravity1.05-1.09
LustreResinous

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Beryl

VarietiesAquamarine (light blue, dark blue, blue-green)
Emerald (green, green-yellow, green-blue)
Goshenite (colourless)
Golden beryl (yellow, yellow-green, golden-yellow)
Morganite (pink to violet)
Chemical CompositionBe3AI2(SiO3)6 Beryllium aluminum silicate
Crystal SystemHexagonal
HabitPrismatic
CleavageVery difficult in one direction, rarely seen
FractureConchoidal
Hardness7.25-7.75
Optic NatureUniaxial Negative
Refractive Index1.577-1.583 (+ or - 0.017)
Birefringence0.005-0.009
DispersionLow, 0.014
Specific Gravity2.72 (+0.18, -0.05)
LustreVitreous to resinous
PleochroismWeak to moderate

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Chrysoberyl

VarietiesGreen, yellow, brown, red
Alexandrite (colour change)
Chemical CompositionBeAI2O4
Crystal SystemOrthorhombic
HabitPseudo-hexagonal twins
CleavageWeak to moderate
FractureConchoidal to uneven
Hardness8.5
Optic NatureBiaxial Positive
Refractive Index1.74-1.75
Birefringence0.009
DispersionLow, 0.014
Specific Gravity3.72
LustreBright vitreous
PleochroismModerate to strong

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Corundum

VarietiesRuby (red)
Sapphire (blue, green, purple, yellow, orange, colourless)
Chemical CompositionAI2O3
Crystal SystemTrigonal
HabitPrismatic, tabular
CleavageNone; twinned stones may show parting
FractureConchoidal
Hardness9
Optic NatureUniaxial Negative
Refractive Index1.762-1.770 (+.009,-.005)
Birefringence0.008-0.010
DispersionLow, 0.018
Specific Gravity3.99
LustreVitreous to Sub adamantine
PleochroismWeak to moderate

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Fluorite

Chemical CompositionCaF2 Calcium fluoride
Crystal SystemCubic
HabitOctahedral, cubes, interpenetrant twins
CleavagePerfect, octahedral
Hardness4
Optic NatureIsotropic
Refractive Index1.434
BirefringenceIsotropic
DispersionVery low, 0.007
Specific Gravity3.18
LustrePoor citreous
FluorescenceBluish-white, purple (LW)

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Garnet

Chemical CompositionX3Y2(SiO4)3
X site is divalent (+2) and can be: ferrous iron, calcium, manganese, magnesium.
Y site is trivalent (+3) and can be: ferric iron, aluminum, chromium, titanium.
Crystal SystemCubic
HabitDodecahedra
CleavageNone
Hardness6.5-8.0
Optic NatureIsotropic
Refractive Index1.73-1.89
BirefringenceNone
Specific Gravity3.40-4.18
LustreVitreous to sub-adamantine

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Jadeite Jade

VarietiesGreen, lilac, white, pink, brown, red, blue, black, orange, yellow.
Chemical CompositionNaAl(SiO3)2
Crystal SystemMonoclinic
HabitPolycrystalline
FractureSplintery
Hardness6.5-7
Specific Gravity3.30-3.37
LustreGreasy to vitreous

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Lapis Lazuli

Chemical CompositionLazurite, hauyne, calcite and pyrite
HabitAggregate
FractureUneven
Hardness5.5
Refractive Index1.500 - 1.670
Specific Gravity2.50 - 3.00
LustreResinous to vitreous

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Malachite

VarietiesBanded light and dark green
Chemical CompositionCu2(CO3)(OH)2
Crystal SystemMonoclinic
HabitBotryoidal, stalactitic, globular
CleavageDistinct
FractureConchoidal, splintery
Hardness3.5-4
Optic NatureBiaxial Negative
Refactive Index1.655 - 1.909
Birefringence0.254
DispersionWeak
Specific Gravity3.60 - 4.05
LustreDull, silky, vitreous
TransparencyTranslucent to opaque
PleochroismNone

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Nephrite Jade

VarietiesGreen to black
Chemical CompositionComplex Ca Mg/Fe (calcium magnesium/iron) silicate
Crystal SystemMonoclinic
HabitPolycrystalline
FractureSplintery
Hardness6.5
Refractive Index+/- 1.62
Specific Gravity2.90 - 3.20
LustreGreasy to vitreous

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Opal

VarietiesPrecious opal (white opal, black opal, boulder opal, jelly opal, crystal opal) all with play of colour.
Fire opal (yellow to orange brown) no play of colour
Chemical CompositionSiO2+H2O
Crystal SystemAmorphous
Hardness5 - 6.5
Refractive Index1.45 (+.020;-0.080)
Specific Gravity2.15 (+0.07;-0.90)
LustreVitreous
PhenomenonPlay of Color

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Peridot

VarietiesYellow-green, olive-green, brownish-green
Chemical Composition(Mg,Fe)2SiO4
Crystal SystemOrthorhombic
HabitPrismatic
CleavagePoor
FractureConchoidal
Hardness6.5
Optic NatureBiaxial Positive
Refractive Index1.65 - 1.69
Birefringence0.036
DispersionMedium, 0.020
Specific Gravity3.34
LustreVitreous
PleochroismWeak

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Pyralspite

CompositionRefractive IndexSpecific GravityHardnessDispersionColour
PyropeMg3AI2(SiO4)31.73 to 1.763.65 to 3.847.50.022Transparent red, purple red. Allochromatic (Cr, Fe)
AlmandineFe3AI2(SiO4)31.76 to 1.814.09 to 4.317.0 to 8.00.027Transparent brown-red to purple red. Idiochromatic (Fe)
SpessariteMn3Al2(SiO4)31.80 to 1.824.186.5 to 7.50.027Transparent orange, red-orange. Idiochromatic (Mn)

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Quartz (Crystalline)

VarietiesAmethyst (purple)
Ametrine (half purple half yellow)
Citrine (yellow, golden-yellow)
Prasiolite (green)
Rock crystal (colourless)
Rose quartz (pink)
Smokey quartz (smokey brown, grey, black)
Chemical CompositionSiO2 Silicon dioxide
Crystal SystemTrigonal
HabitPrismatic
CleavagePoor
FractureConchoidal
Hardness7
Optic NatureUniaxial Positive
Refractive Index1.544 - 1.553
Birefringence0.009
Dispersion0.013
Specific Gravity2.65
LustreVitreous
PleochroismNone

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Spinel

VarietiesColourless, green, blue, red, black
Chemical CompositionMg(Al2O4) Magnesium aluminum oxide
Crystal SystemCubic
HabitOctahedral, contact twins
CleavageImperfect
FractureConchoidal, uneven
Hardness8
Optic NatureIsotropic
Refractive Index1.712 - 1.736
BirefringenceNone
Dispersion0.026
Specific Gravity3.58 - 3.61
LustreVitreous
PleochroismNone

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Spodumene

VarietiesHiddenite (yellow to green)
Kunzite (pink to violet)
Chemical CompositionLiA(SiO3)2
Crystal SystemMonoclinic
HabitPrismatic, tabular
CleavagePerfect, prismatic
FractureUneven
Hardness7
Optic NatureBiaxial Positive
Refractive Index1.66 - 1.68
Birefringence0.015
DispersionLow, 0.017
Specific Gravity3.18
LustreVitreous
PleochroismStrong

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Topaz

VarietiesColourless, yellow, green, blue, red, pink, orange, brown
Chemical CompositionAl2(F,OH)2SiO4
Crystal SystemOrthorhombic
HabitPrismatic with pyramid/domed terminations
CleavagePerfect, basal plane
FractureSub-conchoidal to uneven
Hardness8
Optic NatureBiaxial Positive
Refractive Index1.606 - 1.644
Birefringence0.008 - 0.010
DispersionLow, 0.014
Specific Gravity3.49 - 3.57
LustreVitreous
PleochroismDistinct to strong (depending on body color)

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Tourmaline

VarietiesAll colours, bi-colour, tri-colour
Chemical CompositionComplex borosilicate
Crystal SystemTrigonal
HabitTrigonal prisms with convex faces
FractureConchoidal
Hardness7.5
Optic NatureUniaxial Negative
Refractive Index1.62 - 1.64
Birefringence0.014 - 0.021 (up to 0.039)
DispersionLow, 0.018
Specific Gravity3.06 (3.01-3.11)
LustreVitreous
PleochroismWeak to Strong

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Turquoise

Chemical CompositionCuAl6(PO4)4(OH)8.5H2O
Crystal SystemTriclinic
HabitBotryoidal, massive, microcrystalline to granular
FractureConchoidal
Hardness5.0 - 6.0
Refractive Index1.610 - 1.650
Specific Gravity2.30-2.90
LustreWaxy

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