| Material | Group | Formula | Crystal system | Mohs | RI | SG | Sources |
|---|
| Bone |
|
Ca5(PO4)3(OH) (hydroxyapatite) with collagen; roughly 60-70% mineral in a protein matrix |
None (biological composite, non-crystalline) |
2.5 |
1.5400-1.5500 |
1.900-2.200 |
wiki |
| Horn |
|
Keratin (fibrous structural protein) with traces of calcium and pigment |
None (biological, non-crystalline) |
2.5 |
1.5600-1.5600 |
1.700-1.850 |
wiki |
| Ivory |
|
Ca5(PO4)3(OH) (hydroxyapatite, about 65%) with collagen and elastin (about 35%); ivory is dentine |
None (biological composite, amorphous) |
2.3-2.8 |
1.5350-1.5400 |
1.700-2.000 |
wiki |
| Lapis Lazuli |
|
Rock; chief mineral lazurite Na7Ca(Al6Si6O24)(SO4)(S3)·H2O with calcite, pyrite, sodalite ± hauyne, diopside |
- |
5.0-6.0 |
1.5000-1.6700 |
2.500-3.000 |
GIAmindatwiki |
| Maw Sit Sit |
|
Rock; chief constituent kosmochlor NaCrSi2O6 with chromian jadeite, albite feldspar, amphibole and chlorite |
- |
6.0-7.0 |
1.5200-1.7400 |
2.450-3.150 |
mindatwiki |
| Ruby-in-Zoisite (Anyolite) |
|
Zoisite Ca2Al3(SiO4)3(OH) with ruby Al2O3 and pargasite (amphibole) |
- |
6.0-7.0 |
1.6910-1.7000 |
3.300-3.450 |
GIAmindatwiki |
| Tortoiseshell |
|
Keratin (beta-keratin protein) with embedded pigment granules |
None (biological, amorphous) |
2.5 |
1.5500-1.5500 |
1.260-1.350 |
wiki |
| Vegetable Ivory (Tagua) |
|
Cellulose and hemicellulose (plant endosperm of tagua palm nuts); no mineral |
None (plant tissue, non-crystalline) |
2.5 |
1.5400-1.5400 |
1.380-1.420 |
wiki |
| Kyanite |
Al2SiO5 polymorphs (with andalusite and sillimanite) |
Al2SiO5 |
Triclinic |
4.0-7.5 |
1.7160-1.7310 |
3.550-3.680 |
mindatwiki |
| Andalusite |
Al2SiO5 polymorphs (with kyanite and sillimanite) |
Al2SiO5 |
Orthorhombic |
7.0-7.5 |
1.6340-1.6430 |
3.130-3.210 |
GIAmindatwiki |
| Unakite |
Altered granite |
Rock: pink orthoclase feldspar + green epidote + quartz (composition varies) |
- |
6.0-7.0 |
1.5200-1.7600 |
2.850-3.200 |
mindatwiki |
| Apatite |
Apatite |
Ca5(PO4)3(F,OH,Cl) |
Hexagonal |
5.0 |
1.6340-1.6380 |
3.130-3.230 |
mindatwiki |
| Beryl |
Beryl |
Be3Al2Si6O18 |
Hexagonal |
7.5-8.0 |
1.5770-1.5830 |
2.670-2.900 |
GIAmindatwiki |
| Howlite |
Borates (inoborate) |
Ca2B5SiO9(OH)5 |
Monoclinic |
3.5 |
1.5860-1.6050 |
2.450-2.580 |
GIAmindatwiki |
| Diamond |
Carbon |
C |
Cubic |
10.0 |
2.4170-2.4170 |
3.510-3.530 |
GIAmindatwiki |
| Malachite |
Carbonate |
Cu2CO3(OH)2 |
Monoclinic |
3.5-4.0 |
1.6550-1.9090 |
3.250-4.100 |
GIAmindatwiki |
| Rhodochrosite |
Carbonate |
MnCO3 |
Trigonal |
3.5-4.0 |
1.5970-1.8170 |
3.450-3.700 |
GIAmindatwiki |
| Calcite |
Carbonate (calcite group) |
CaCO3 |
Trigonal |
3.0 |
1.4860-1.6580 |
2.650-2.750 |
GIAmindatwiki |
| Magnesite |
Carbonate (calcite group) |
MgCO3 |
Trigonal |
3.5-4.5 |
1.5090-1.7000 |
3.000-3.200 |
GIAmindatwiki |
| Chrysoberyl |
Chrysoberyl |
BeAl2O4 |
Orthorhombic |
8.5 |
1.7460-1.7550 |
3.710-3.750 |
GIAmindatwiki |
| Coral |
Cnidarian (colonial marine animal skeleton) |
Calcareous type: CaCO3 (magnesian calcite). Conchiolin/horny type: protein (conchiolin) |
None (polycrystalline aggregate of calcite/aragonite fibres) |
3.0-4.0 |
1.4860-1.6580 |
2.600-2.700 |
GIAwiki |
| Iolite |
Cordierite |
Mg2Al4Si5O18 |
Orthorhombic |
7.0-7.5 |
1.5420-1.5510 |
2.560-2.660 |
GIAmindatwiki |
| Corundum |
Corundum |
Al2O3 |
Trigonal |
9.0 |
1.7620-1.7700 |
3.950-4.100 |
GIAmindatwiki |
| Sugilite |
Cyclosilicate |
KNa2(Fe,Mn,Al)2Li3Si12O30 |
Hexagonal |
5.5-6.5 |
1.6070-1.6100 |
2.690-2.800 |
GIAmindatwiki |
| Zoisite |
Epidote |
Ca2Al3(SiO4)3(OH) |
Orthorhombic |
6.0-7.0 |
1.6910-1.7000 |
3.100-3.450 |
GIAmindatwiki |
| Epidote |
Epidote group (with clinozoisite, zoisite, piemontite, allanite) |
Ca2(Al,Fe)3(SiO4)3(OH) |
Monoclinic |
6.0-7.0 |
1.7290-1.7680 |
3.250-3.500 |
GIAmindatwiki |
| Microcline Feldspar |
Feldspar |
KAlSi3O8 |
Triclinic |
6.0-6.5 |
1.5220-1.5300 |
2.540-2.580 |
mindatwiki |
| Orthoclase Feldspar |
Feldspar |
KAlSi3O8 |
Monoclinic |
6.0-6.5 |
1.5180-1.5260 |
2.550-2.610 |
GIAmindatwiki |
| Labradorite Feldspar |
Feldspar (plagioclase series) |
(Ca,Na)(Al,Si)4O8 (50-70 percent anorthite component) |
Triclinic |
6.0-6.5 |
1.5590-1.5680 |
2.650-2.750 |
GIAmindatwiki |
| Oligoclase Feldspar |
Feldspar (plagioclase series) |
(Na,Ca)(Al,Si)4O8 (10-30 percent anorthite component) |
Triclinic |
6.0-6.5 |
1.5370-1.5470 |
2.620-2.670 |
GIAmindatwiki |
| Sodalite |
Feldspathoid (sodalite group) |
Na8(Al6Si6O24)Cl2 |
Cubic |
5.5-6.0 |
1.4830-1.4830 |
2.150-2.400 |
GIAmindatwiki |
| Ammonite |
Fossil (ammonoid shell; gem layer is ammolite) |
CaCO3 (aragonite) with variable calcite, pyrite, silica and trace elements |
Aragonite (orthorhombic) occurring as stacked sub-microscopic platelets - reads as aggregate |
3.5-4.5 |
1.5200-1.6800 |
2.600-2.850 |
wiki |
| Almandine Garnet |
Garnet |
Fe3Al2(SiO4)3 |
Cubic |
7.0-7.5 |
1.7700-1.8200 |
3.950-4.300 |
GIAmindatwiki |
| Andradite Garnet |
Garnet |
Ca3Fe2(SiO4)3 |
Cubic |
6.5-7.0 |
1.8800-1.8890 |
3.810-3.900 |
GIAmindatwiki |
| Grossular Garnet |
Garnet |
Ca3Al2(SiO4)3 |
Cubic |
6.5-7.5 |
1.7300-1.7600 |
3.570-3.730 |
GIAmindatwiki |
| Hydrogrossular Garnet |
Garnet |
Ca3Al2(SiO4)3-x(OH)4x |
Cubic |
6.5-7.0 |
1.6700-1.7300 |
3.150-3.550 |
GIAmindatwiki |
| Pyrope Garnet |
Garnet |
Mg3Al2(SiO4)3 |
Cubic |
7.0-7.5 |
1.7140-1.7420 |
3.620-3.870 |
GIAmindatwiki |
| Rhodolite Garnet |
Garnet |
(Mg,Fe)3Al2(SiO4)3 |
Cubic |
7.0-7.5 |
1.7400-1.7800 |
3.740-3.940 |
GIAmindatwiki |
| Spessartine Garnet |
Garnet |
Mn3Al2(SiO4)3 |
Cubic |
7.0-7.5 |
1.7900-1.8100 |
4.120-4.200 |
GIAmindatwiki |
| Tsavorite Garnet |
Garnet |
Ca3Al2(SiO4)3 |
Cubic |
7.0-7.5 |
1.7300-1.7400 |
3.600-3.680 |
GIAmindatwiki |
| Charoite |
Gem rock dominated by the mineral charoite (charoitite) |
(K,Na)5(Ca,Ba,Sr)8(Si6O15)2(Si4O9)(OH,F)·11H2O (mineral charoite) |
Monoclinic |
5.0-6.0 |
1.5500-1.5590 |
2.540-2.780 |
GIAmindatwiki |
| Fluorite |
Halide |
CaF2 |
Cubic |
4.0 |
1.4340-1.4340 |
3.000-3.250 |
mindatwiki |
| Chrysocolla |
Hydrous copper silicate (phyllosilicate/mineraloid) |
(Cu,Al)2H2Si2O5(OH)4·nH2O |
Amorphous to orthorhombic (mineraloid; structure debated) |
2.0-4.0 |
1.4600-1.5700 |
1.900-2.400 |
GIAmindatwiki |
| Jadeite |
Jade |
NaAlSi2O6 |
Monoclinic |
6.5-7.0 |
1.6600-1.6800 |
3.250-3.400 |
GIAmindatwiki |
| Nephrite |
Jade |
Ca2(Mg,Fe)5Si8O22(OH)2 |
Monoclinic |
6.0-6.5 |
1.6060-1.6320 |
2.900-3.100 |
GIAmindatwiki |
| Glass (gem imitation) |
Man-made product |
Amorphous silica (SiO2) melt with fluxes, stabilisers and colourants; high-lead 'strass' variants for brilliancy |
Amorphous |
5.0-6.0 |
1.4700-1.7000 |
2.300-4.500 |
GIAmindatwiki |
| Hematine (Imitation Hematite) |
Man-made product |
Man-made ceramic iron oxide, commonly barium-strontium ferrite composites (contains no natural hematite crystal material despite the name) |
- |
5.0-6.5 |
- |
4.900-5.300 |
GIAmindatwiki |
| Plastic (gem imitation) |
Man-made product |
Amorphous organic polymers (varies: acrylic, polystyrene, celluloid, phenolic/Bakelite, epoxy, polyester) |
Amorphous |
1.5-3.0 |
1.4600-1.7000 |
1.050-1.550 |
GIAmindatwiki |
| Strontium Titanate |
Man-made product (diamond simulant) |
SrTiO3 (synthetic tausonite-structure perovskite) |
Cubic |
5.0-6.0 |
2.4090-2.4090 |
5.110-5.150 |
GIAmindatwiki |
| GGG (Gadolinium Gallium Garnet) |
Man-made product (synthetic garnet-structure crystal) |
Gd3Ga5O12 |
Cubic |
6.5 |
1.9700-1.9700 |
6.950-7.090 |
GIAmindatwiki |
| YAG (Yttrium Aluminium Garnet) |
Man-made product (synthetic garnet-structure crystal) |
Y3Al5O12 |
Cubic |
8.3 |
1.8330-1.8330 |
4.500-4.600 |
GIAmindatwiki |
| Shell |
Mollusc (bivalve and gastropod shell) |
CaCO3 (as aragonite and/or calcite) with conchiolin (organic binder) and water |
None (polycrystalline biological aggregate) |
3.5 |
1.5300-1.6850 |
2.700-2.890 |
wiki |
| Pearl |
Mollusc (nacreous pearl) |
CaCO3 (mostly aragonite, some calcite) with conchiolin binder and 2-4% water |
None (aggregate of microscopic aragonite platelets in an organic matrix) |
2.5-4.5 |
1.5200-1.6900 |
2.600-2.850 |
GIAwiki |
| Calcareous Concretions |
Mollusc (non-nacreous pearl-like concretions) |
CaCO3 (coarser aragonite/calcite crystals than nacre) with organic matter and water |
None (porcellaneous biological aggregate) |
2.5-4.0 |
1.5300-1.6850 |
2.810-2.870 |
wiki |
| Obsidian |
Natural volcanic glass |
Silica-rich rhyolitic glass (about 70%+ SiO2 with Al, Na, K, Fe) |
Amorphous (glass) |
5.0-5.5 |
1.4800-1.5100 |
2.330-2.500 |
GIAmindatwiki |
| Peridot |
Olivine |
(Mg,Fe)2SiO4 |
Orthorhombic |
6.5-7.0 |
1.6540-1.6900 |
3.270-3.480 |
GIAmindatwiki |
| Amber |
Organic (fossil tree resin) |
Organic resin, approx C10H16O; Baltic succinite additionally contains 3-8% succinic acid |
Amorphous (none — organic) |
2.0-2.5 |
1.5400-1.5400 |
1.040-1.100 |
GIAmindatwiki |
| Jet |
Organic (fossilised wood — gem-quality lignite) |
Organic: primarily C with H and O (fossilised conifer wood, Araucariaceae) |
Amorphous (none — organic) |
2.5-4.0 |
1.6400-1.6800 |
1.300-1.340 |
GIAmindatwiki |
| Copal |
Organic (immature tree resin) |
Organic resin — diterpenoid and triterpenoid hydrocarbons (no succinic acid) |
Amorphous (none — organic) |
2.0 |
1.5300-1.5400 |
1.030-1.100 |
GIAmindatwiki |
| Hematite |
Oxide (hematite group) |
Fe2O3 |
Trigonal |
5.5-6.5 |
2.8700-3.2200 |
4.900-5.300 |
GIAmindatwiki |
| Turquoise |
Phosphate |
CuAl6(PO4)4(OH)8·4H2O |
Triclinic |
5.0-6.0 |
1.6100-1.6500 |
2.400-2.900 |
GIAmindatwiki |
| Variscite |
Phosphate |
AlPO4·2H2O |
Orthorhombic |
4.5-5.0 |
1.5600-1.5900 |
2.500-2.610 |
GIAmindatwiki |
| Diopside |
Pyroxene (clinopyroxene) |
CaMgSi2O6 |
Monoclinic |
5.5-6.0 |
1.6750-1.7010 |
3.220-3.400 |
GIAmindatwiki |
| Rhodonite |
Pyroxenoid (inosilicate) |
(Mn,Fe,Mg,Ca)SiO3 |
Triclinic |
5.5-6.5 |
1.7330-1.7470 |
3.500-3.760 |
GIAmindatwiki |
| Chalcedony |
Quartz |
SiO2 |
Trigonal |
6.5-7.0 |
1.5300-1.5390 |
2.550-2.700 |
GIAmindatwiki |
| Quartz |
Quartz |
SiO2 |
Trigonal |
7.0 |
1.5440-1.5530 |
2.640-2.690 |
GIAmindatwiki |
| Serpentine |
Serpentine |
(Mg,Fe,Ni)3Si2O5(OH)4 |
Monoclinic (antigorite) to trigonal (lizardite); gem material is massive aggregate |
2.5-5.5 |
1.5600-1.5700 |
2.440-2.800 |
GIAmindatwiki |
| Opal |
Silica |
SiO2·nH2O |
Amorphous |
5.0-6.5 |
1.3700-1.4700 |
1.980-2.230 |
GIAmindatwiki |
| Spinel |
Spinel |
MgAl2O4 |
Cubic |
8.0 |
1.7120-1.7360 |
3.580-3.980 |
GIAmindatwiki |
| Spodumene |
Spodumene |
LiAlSi2O6 |
Monoclinic |
6.5-7.0 |
1.6600-1.6760 |
3.150-3.210 |
GIAmindatwiki |
| Pyrite |
Sulfide (pyrite group) |
FeS2 |
Cubic (isometric) |
6.0-6.5 |
- |
4.800-5.200 |
GIAmindatwiki |
| Cubic Zirconia (CZ) |
Synthetic |
ZrO2, cubic-stabilised with ~10% yttrium oxide (Y2O3) or calcium oxide |
Cubic |
8.0-8.5 |
2.1500-2.1800 |
5.600-6.000 |
GIAmindatwiki |
| Synthetic Moissanite |
Synthetic |
SiC (silicon carbide, gem material is the 6H polytype) |
Hexagonal |
9.3 |
2.6500-2.6900 |
3.150-3.220 |
GIAmindatwiki |
| Synthetic Opal |
Synthetic |
SiO2.nH2O (same hydrous silica as natural opal) |
Amorphous |
4.5-6.0 |
1.4300-1.4700 |
1.970-2.200 |
GIAmindatwiki |
| Synthetic Quartz |
Synthetic |
SiO2 |
Trigonal (hexagonal crystallographic axes) |
7.0 |
1.5440-1.5530 |
2.630-2.670 |
GIAmindatwiki |
| Synthetic Rutile |
Synthetic |
TiO2 (titanium dioxide) |
Tetragonal |
6.0-6.5 |
2.6160-2.9030 |
4.230-4.290 |
GIAmindatwiki |
| Synthetic Spinel |
Synthetic |
MgO.Al2O3 - commercial flame-fusion material is deliberately alumina-rich (non-stoichiometric), which raises its RI |
Cubic |
8.0 |
1.7250-1.7320 |
3.520-3.660 |
GIAmindatwiki |
| Moldavite |
Tektite (natural impact glass) |
SiO2 (about 75-80% silica glass with Al2O3, FeO and alkalis) |
Amorphous (glass) |
5.0-5.5 |
1.4800-1.5100 |
2.320-2.400 |
GIAmindatwiki |
| Sphene (Titanite) |
Titanite group |
CaTiSiO5 |
Monoclinic |
5.0-5.5 |
1.9000-2.0340 |
3.500-3.540 |
GIAmindatwiki |
| Topaz |
Topaz |
Al2SiO4(F,OH)2 |
Orthorhombic |
8.0 |
1.6190-1.6270 |
3.490-3.570 |
GIAmindatwiki |
| Tourmaline |
Tourmaline |
Na(Li,Al)3Al6(BO3)3Si6O18(OH)4 (elbaite) |
Trigonal |
7.0-7.5 |
1.6240-1.6440 |
3.000-3.260 |
GIAmindatwiki |
| Idocrase (Vesuvianite) |
Vesuvianite group |
Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4 |
Tetragonal |
6.5 |
1.7130-1.7180 |
3.320-3.450 |
mindatwiki |
| Zircon |
Zircon |
ZrSiO4 |
Tetragonal |
6.0-7.5 |
1.7800-1.9840 |
3.900-4.730 |
GIAmindatwiki |