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Amber

 Chemical Composition  C-H-O compound (fossil resin)
 Crystal System  Amorphous
 Fracture  Conchoidal, brittle
 Hardness  2-2.5
 Refractive Index  1.54
 Specific Gravity  1.05-1.09
 Lustre  Resinous

beryl

 Varieties  Aquamarine(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 Composition  Be3Al2(SiO3)6 Beryllium aluminum silicate
 Crystal System  Hexagonal
 Habit  Prismatic
 Cleavage  Very difficult in one direction, rarely seen
 Fracture  Conchoidal
 Hardness  7.25-7.75
 Optic Nature  Uniaxial Negative
 Refractive Index  1.577-1.583
(+ or - 0.017)
 Birefringence  0.005-0.009
 Dispersion  Low, 0.014
 Specific Gravity  2.72
(+0.18,- 0.05)
 Lustre  Vitreous to resinous
 Pleochroism  Weak to moderate

Chrysoberyl

 Varieties  Green, yellow, brown, red
   Alexandrite (colour change)
 Chemical Composition  BeAl2O4
 Crystal System  Orthorhombic
 Habit  Pseudo-hexagonal twins
 Cleavage  Weak to moderate
 Fracture  Conchoidal to uneven
 Hardness  8.5
 Optic Nature  Biaxial Positive
 Refractive Index  1.74-1.75
 Birefringence  0.009
 Dispersion  Low, 0.014
 Specific Gravity  3.72
 Lustre  Bright vitreous
 Pleochroism  Moderate to strong

corundum

 Varieties  Ruby (red)
   Sapphire (blue, green, purple, yellow, orange, colourless)
 Chemical Composition  Al2O3
 Crystal System  Trigonal
 Habit  Prismatic, tabular
 Cleavage  None; twinned stones may show parting
 Fracture  Conchoidal
 Hardness  9
 Optic Nature  Uniaxial Negative
 Refractive Index  1.762-1.770
(+.009,-.005)
 Birefringence  0.008-0.010
 Dispersion  Low, 0.018
 Specific Gravity  3.99
 Lustre  Vitreous to Sub adamantine
 Pleochroism  Weak to moderate

Fluorite

 Chemical Composition  CaF2 Calcium fluoride
 Crystal System  Cubic
 Habit  Octahedral, cubes, interpenetrant twins
 Cleavage  Perfect, octahedral
 Hardness  4
 Optic Nature  Isotropic
 Refractive Index  1.434
 Birefringence  Isotropic
 Dispersion  Very low, 0.007
 Specific Gravity  3.18
 Lustre  Poor vitreous
 Fluorescence  Bluish-white, purple (LW)

garnet

 Chemical Composition X3Y2(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 System  Cubic
 Habit  Dodecahedra
 Cleavage  None
 Hardness  6.5-8.0
 Optic Nature  Isotropic
 Refractive Index  1.73-1.89
 Birefringence  None
 Specific Gravity  3.40-4.18
 Lustre  Vitreous to sub-adamantine

There are two major isomorphous series of garnet:


pyralspite series

(Y site is aluminum, X site has isomorphous replacement)

   Composition  Refractive Index  Specific Gravity  Hardness  Dispersion Colour
 Pyrope  Mg3Al2(SiO4)3  1.73 to 1.76  3.65 to 3.84  7.5  0.022 Transparent red, purple red. Allochromatic (Cr, Fe)
 Almandine  Fe3Al2(SiO4)3  1.76 to 1.81  4.09 to 4.31  7.0 to 8.0  0.027 Transparent brown-red to purple red. Idiochromatic (Fe)
 Spessarite  Mn3Al2(SiO4)3  1.80 to 1.82  4.18  6.5 to 7.5  0.027 Transparent orange, red-orange. Idiochromatic (Mn)

ugrandite series

(X site is calcium, Y site has isomorphous replacement)

   Composition  Refractive Index  Specific Gravity  Hardness  Dispersion Colour
 Uvarovite  Ca3Cr2(SiO4)3  1.86  3.40 to 3.80  6.5 to 7.0  0.027 Emerald green. Idiochromatic (Cr)
 Grossular  Ca3Al2(SiO4)3  1.734 to 1.75  3.42 to 3.72  6.5 to 7.0  0.027 Colourless when pure
 Grossular
(Hessonite)
   1.74 to 1.75  3.60 to 3.70  6.5 to 7.0  0.027 Brown-red. Allochromatic (Mn, Fe)
 Grossular
(Tsavorite)
   1.74 to 1.75  3.65  6.5 to 7.0  0.027 Green. Allochromatic (V, Cr)
 Andradite  Ca3Fe2(SiO4)3  1.87 to 1.89  3.70 to 4.10  6.5 to 7.0  0.057 Green-brown, brown-yellow
 Andradite
(Demantoid)
   1.87 to 1.89  3.70 to 4.10  6.5 to 7.0  0.057 Bright green. Allochromatic (Cr)

There are no true end members in the garnet series' where one of the sites (X or Y) is 100% one element, the chemical compositions above are only ideal portrayals of a pure garnet variety. Garnets in each series fall somewhere in between the ideal which is why there is a range of refractive index and specific gravity values for each variety. Size discrepancy between the X and Y sites generally prohibits substitution between the series' for the most part, but some substitution can occur.

Jadeite Jade

 Varieties  Green, lilac, white, pink, brown, red, blue, black, orange, yellow
 Chemical Composition  NaAl(SiO3)2
 Crystal System  Monoclinic
 Habit  Polycrystalline
 Fracture  Splintery
 Hardness  6.5 -7
 Specific Gravity  3.30 - 3.37
 Lustre  Greasy to vitreous

Lapis Lazuli

 Chemical Composition  Lazurite, hauyne, calcite and pyrite
 Habit  Aggregate
 Fracture  Uneven
 Hardness  5.5
 Refractive Index  1.500 - 1.670
 Specific Gravity  2.50 - 3.00
 Lustre  Resinous to vitreous

Malachite

 Varieties  Banded light and dark green
 Chemical Composition  Cu2(CO3)(OH)2
 Crystal System  Monoclinic
 Habit  Botryoidal, stalactitic, globular
 Cleavage  Distinct
 Fracture  Conchoidal, splintery
 Hardness  3.5-4
 Optic Nature  Biaxial Negative
 Refractive Index  1.655 - 1.909
 Birefringence  0.254
 Dispersion  Weak
 Specific Gravity  3.60 - 4.05
 Lustre  Dull, silky, vitreous
 Transparency  Translucent to opaque
 Pleochroism  None

Nephrite Jade

 Varieties  Green to black
 Chemical Composition  Complex Ca Mg/Fe (calcium magnesium/iron) silicate
 Crystal System  Monoclinic
 Habit  Polycrystalline
 Fracture  Splintery
 Hardness  6.5
 Refractive Index  ±1.62
 Specific Gravity  2.90 - 3.20
 Lustre  Greasy to vitreous

Opal

 Varieties  Precious 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 Composition  SiO2+H2O
 Crystal System  Amorphous
 Hardness  5 - 6 1/2
 Refractive Index  1.45 (+.020;-0.080)
 Specific Gravity  2.15 (+0.07;-0.90)
 Lustre  Vitreous
 Phenomenon  Play of Color

Peridot

 Varieties  Yellow-green, olive-green, brownish-green
 Chemical Composition  (Mg,Fe)2SiO4
 Crystal System  Orthorhombic
 Habit  Prismatic
 Cleavage  Poor
 Fracture  Conchoidal
 Hardness  6.5
 Optic Nature  Biaxial Positive
 Refractive Index  1.65 - 1.69
 Birefringence  0.036
 Dispersion  Medium, 0.020
 Specific Gravity  3.34
 Lustre  Vitreous
 Pleochroism  Weak

Spinel

 Varieties  Colourless, green, blue, red, black
 Chemical Composition  Mg(Al2O4) Magnesium aluminum oxide
 Crystal System  Cubic
 Habit  Octahedral, contact twins
 Cleavage  Imperfect
 Fracture  Conchoidal, uneven
 Hardness  8
 Optic Nature  Isotropic
 Refractive Index  1.712 - 1.736
 Birefringence  None
 Dispersion  0.026
 Specific Gravity  3.58 - 3.61
 Lustre  Vitreous
 Pleochroism  None

Spodumene

 Varieties  Hiddenite (yellow to green)
   Kunzite (pink to violet)
 Chemical Composition  LiAl(SiO3)2
 Crystal System  Monoclinic
 Habit  Prismatic, tabular
 Cleavage  Perfect, prismatic
 Fracture  Uneven
 Hardness  7
 Optic Nature  Biaxial Positive
 Refractive Index  1.66-1.68
 Birefringence  0.015
 Dispersion  Low, 0.017
 Specific Gravity  3.18
 Lustre  Vitreous
 Pleochroism  Strong

quartz (crystalline)

 Varieties  Amethyst (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 Composition  SiO2 Silicon dioxide
 Crystal System  Trigonal
 Habit  Prismatic
 Cleavage  Poor
 Fracture  Conchoidal
 Hardness  7
 Optic Nature  Uniaxial Positive
 Refractive Index  1.544 - 1.553
 Birefringence  0.009
 Dispersion  0.013
 Specific Gravity  2.65
 Lustre  Vitreous
 Pleochroism  None

Quartz (Polycrystalline)

 Varieties  Aventurine (green with mica inclusions)
   Tigers eye/Hawks eye (golden-yellow, golden-brown, blue-gray, blue-green)
   Chalcedony
- Blue, white, grey
- Carnelian (brownish red to orange)
- Chrysoprase (green)
- Bloodstone (dark green with red spots)
- Agate (all colours, usually banded)
- Onyx (layer stone)
- Jasper (all colours, usually striped or spotted)
- Petrified wood
 Chemical Composition  SiO2 Silicon dioxide
 Crystal System  Trigonal
 Habit  Prismatic
 Cleavage  Poor
 Fracture  Conchoidal
 Hardness  7
 Optic Nature  Uniaxial Positive
 Refractive Index  1.544 - 1.553
 Birefringence  0.009
 Dispersion  0.013
 Specific Gravity  2.65
 Lustre  Vitreous
 Pleochroism  None

Topaz

 Varieties  Colourless, yellow, green, blue, red, pink, orange, brown
 Chemical Composition  Al2(F,OH)2SiO4
 Crystal System  Orthorhombic
 Habit  Prismatic with pyramidal/domed terminations
 Cleavage  Perfect, basal plane
 Fracture  Sub-conchoidal to uneven
 Hardness  8
 Optic Nature  Biaxial Positive
 Refractive Index  1.606-1.644
 Birefringence  0.008 - 0.010
 Dispersion  Low, 0.014
 Specific Gravity  3.49 - 3.57
 Lustre  Vitreous
 Pleochroism  Distinct to strong (depending on body color)

Tourmaline

 Varieties  All colours, bi-colour, tri-colour
 Chemical Composition  Complex borosilicate
 Crystal System  Trigonal
 Habit  Trigonal prisms with convex faces
 Fracture  Conchoidal
 Hardness  7.5
 Optic Nature  Uniaxial Negative
 Refractive Index  1.62 - 1.64
 Birefringence  0.014-0.021 (up to 0.039)
 Dispersion  Low, 0.018
 Specific Gravity  3.06 (3.01-3.11)
 Lustre  Vitreous
 Pleochroism  Weak to strong

Turquoise

 Chemical Composition  CuAl6(PO4)4(OH)8.5H2O
 Crystal System  Triclinic
 Habit  Botryoidal, massive, microcrystalline to granular
 Fracture  Conchoidal
 Hardness  5.0 - 6.0
 Refractive Index  1.610-1.650
 Specific Gravity  2.30-2.90
 Lustre  Waxy

Zircon

 Chemical Composition  ZrSiO4 Zirconium silicate
 Crystal System  Tetragonal
 Habit  Prismatic (squared) with pyramidal terminations
 Cleavage  Poor
 Hardness  7.5
 Optic Nature  Uniaxial Positive to isotropic
 Refractive Index  1.78 - 1.99
 Birefringence  Up to 0.059
 Dispersion  High, 0.039
 Specific Gravity  3.90-4.69
 Lustre  Vitreous to sub-adamantine
 Pleochroism  Weak (stronger in heat-treated)

zoisite

 Varieties  Tanzanite (blue, purple)
   Thulite (opaque pink)
 Chemical Composition  Ca3Al2(SiO4)3 Calcium aluminum silicate
 Crystal System  Orthorhombic
 Habit  Prismatic and massive
 Cleavage  Perfect, prismatic
 Fracture  Uneven
 Hardness  6.5
 Optic Nature  Biaxial +
 Refractive Index  1.685-1.707
 Birefringence  0.008
 Dispersion  Low, 0.012
 Specific Gravity  3.35
 Lustre  Vitreous
 Pleochroism  Strong in blue