| 1 |
Agate |
Quartz |
Agate |
1.530–1.540 |
2.58–2.64 |
6.5–7 |
Uniaxial (+) |
~0.009 |
Dyeing |
Chalcedony berlapis/banded |
| 2 |
Alexandrite |
Chrysoberyl |
Alexandrite |
1.746–1.755 |
3.70–3.73 |
8.5 |
Biaxial (+) |
0.008–0.011 |
Heat |
Color change |
| 3 |
Amazonite |
Microcline |
Amazonite |
1.522–1.530 |
2.54–2.58 |
6–6.5 |
Biaxial (−) |
~0.007 |
— |
Feldspar |
| 4 |
Amber |
Organic |
Amber |
1.530–1.550 |
1.05–1.10 |
2–2.5 |
Aggregate |
— |
Heat, filling |
Organic gem material |
| 5 |
Amethyst |
Quartz |
Amethyst |
1.544–1.553 |
2.65–2.66 |
7 |
Uniaxial (+) |
~0.009 |
Heat |
Purple quartz |
| 6 |
Andalusite |
Andalusite |
Andalusite |
1.629–1.650 |
3.13–3.16 |
7.5 |
Biaxial (−) |
~0.015 |
— |
Strong pleochroism |
| 7 |
Aquamarine |
Beryl |
Aquamarine |
1.564–1.590 |
2.68–2.80 |
7.5–8 |
Uniaxial (−) |
~0.006 |
Heat |
Fe-bearing beryl |
| 8 |
Aventurine Quartz |
Quartz |
Aventurine |
1.544–1.553 |
2.63–2.66 |
7 |
Uniaxial (+) |
~0.009 |
— |
Included quartz |
| 9 |
Azurite |
Azurite |
Azurite |
1.730–1.838 |
3.77–3.89 |
3.5–4 |
Biaxial (+) |
~0.108 |
— |
Very high birefringence |
| 10 |
Beryl |
Beryl |
— |
1.564–1.595 |
2.63–2.92 |
7.5–8 |
Uniaxial (−) |
~0.005–0.007 |
Heat |
Species containing Emerald & Aquamarine |
| 11 |
Bloodstone |
Quartz |
Bloodstone |
1.530–1.540 |
2.58–2.64 |
6.5–7 |
Uniaxial (+) |
~0.009 |
Dyeing possible |
Chalcedony with inclusions |
| 12 |
Carnelian |
Quartz |
Carnelian |
1.530–1.540 |
2.58–2.64 |
6.5–7 |
Uniaxial (+) |
~0.009 |
Heat, dyeing |
Orange-red chalcedony |
| 13 |
Chalcedony |
Quartz |
Chalcedony |
1.530–1.540 |
2.58–2.64 |
6.5–7 |
Aggregate |
— |
Dyeing |
Microcrystalline quartz |
| 14 |
Charoite |
Charoite |
Charoite |
1.550–1.570 |
2.54–2.78 |
5–6 |
Biaxial |
— |
— |
Fibrous structure |
| 15 |
Chrysoberyl |
Chrysoberyl |
— |
1.746–1.755 |
3.70–3.73 |
8.5 |
Biaxial (+) |
0.008–0.011 |
Heat |
Includes Alexandrite |
| 16 |
Citrine |
Quartz |
Citrine |
1.544–1.553 |
2.65–2.66 |
7 |
Uniaxial (+) |
~0.009 |
Heat |
Natural and heated |
| 17 |
Clinozoisite |
Clinozoisite |
— |
1.672–1.724 |
3.30–3.50 |
6–7 |
Biaxial |
~0.015–0.050 |
— |
Epidote-group mineral |
| 18 |
Coral |
Organic |
Coral |
Variable |
2.60–2.70 |
3–4 |
Aggregate |
— |
Dyeing, bleaching |
Organic |
| 19 |
Diamond |
Diamond |
Diamond |
2.417–2.419 |
3.52 |
10 |
Isotropic |
None |
HPHT, CVD, irradiation |
Highest Mohs hardness |
| 20 |
Diopside |
Diopside |
— |
1.664–1.730 |
3.22–3.38 |
5–6 |
Biaxial (+) |
~0.030 |
Heat possible |
Chrome Diopside is green variety |
| 21 |
Emerald |
Beryl |
Emerald |
1.560–1.590 |
2.67–2.78 |
7.5–8 |
Uniaxial (−) |
~0.006 |
Oil, resin |
Cr/V-bearing beryl |
| 22 |
Epidote |
Epidote |
— |
1.720–1.768 |
3.35–3.50 |
6–7 |
Biaxial (−) |
~0.015–0.045 |
— |
Strong pleochroism |
| 23 |
Fluorite |
Fluorite |
— |
1.433–1.435 |
3.18 |
4 |
Isotropic |
None |
Irradiation possible |
Cubic |
| 24 |
Garnet |
Garnet Group |
Various |
1.720–1.890 |
3.50–4.30 |
6.5–7.5 |
Isotropic* |
None* |
Heat possible |
RI/SG vary greatly by species |
| 25 |
Hessonite |
Grossular |
Hessonite |
1.730–1.760 |
3.60–3.70 |
6.5–7.5 |
Isotropic |
None |
Heat possible |
“Cinnamon” garnet |
| 26 |
Iolite |
Cordierite |
Iolite |
1.542–1.578 |
2.58–2.66 |
7–7.5 |
Biaxial (−) |
~0.008–0.012 |
Heat possible |
Strong pleochroism |
| 27 |
Jadeite |
Jadeite |
Jadeite |
1.654–1.667 |
3.30–3.38 |
6.5–7 |
Aggregate / polycrystalline |
~0.012 |
Dye, impregnation, bleaching |
Toughness higher than hardness suggests |
| 28 |
Jasper |
Quartz |
Jasper |
1.530–1.540 |
2.58–2.90 |
6.5–7 |
Aggregate |
— |
Dyeing possible |
Opaque microcrystalline quartz |
| 29 |
Kyanite |
Kyanite |
Kyanite |
1.710–1.734 |
3.53–3.70 |
4.5–7 |
Biaxial (−) |
~0.015 |
— |
Hardness varies by direction |
| 30 |
Labradorite |
Feldspar |
Labradorite |
1.559–1.573 |
2.68–2.72 |
6–6.5 |
Biaxial |
~0.008–0.010 |
— |
Labradorescence |
| 31 |
Lapis Lazuli |
Rock / Lazurite dominant |
Lapis Lazuli |
1.500–1.550 |
2.70–2.90 |
5–5.5 |
Aggregate |
— |
Dyeing, impregnation |
Rock, not single mineral |
| 32 |
Larimar |
Pectolite |
Larimar |
1.600–1.650 |
2.70–2.90 |
4.5–5 |
Biaxial |
Variable |
— |
Blue pectolite |
| 33 |
Malachite |
Malachite |
— |
1.655–1.909 |
3.60–4.05 |
3.5–4 |
Biaxial |
Very high |
Wax, impregnation |
Often banded |
| 34 |
Moldavite |
Natural Glass |
Moldavite |
~1.48–1.54 |
2.32–2.40 |
5.5–6 |
Isotropic |
None |
— |
Impact glass |
| 35 |
Moonstone |
Feldspar |
Moonstone |
1.518–1.526 |
2.55–2.60 |
6–6.5 |
Biaxial |
Variable |
Coating possible |
Adularescence |
| 36 |
Morganite |
Beryl |
Morganite |
1.572–1.590 |
2.71–2.90 |
7.5–8 |
Uniaxial (−) |
~0.006 |
Heat |
Pink beryl |
| 37 |
Nephrite |
Amphibole |
Nephrite |
1.600–1.630 |
2.90–3.10 |
6–6.5 |
Aggregate |
— |
Dye, impregnation |
Very tough fibrous aggregate |
| 38 |
Obsidian |
Natural Glass |
Obsidian |
~1.450–1.550 |
2.35–2.60 |
5–5.5 |
Isotropic |
None |
Heat/coating possible |
Volcanic glass |
| 39 |
Onyx |
Quartz |
Onyx |
1.530–1.540 |
2.58–2.65 |
6.5–7 |
Aggregate |
— |
Dyeing |
Commercial term often broad |
| 40 |
Opal |
Hydrated Silica |
Opal |
1.370–1.470 |
1.98–2.25 |
5.5–6.5 |
Amorphous |
None |
Smoke, sugar-acid, impregnation |
Water content variable |
| 41 |
Peridot |
Olivine |
Peridot |
1.635–1.690 |
3.27–3.37 |
6.5–7 |
Biaxial (+) |
~0.036 |
Heat possible |
Strong birefringence |
| 42 |
Prehnite |
Prehnite |
Prehnite |
1.611–1.669 |
2.80–2.95 |
6–6.5 |
Biaxial (+) |
~0.020 |
— |
Often included |
| 43 |
Pyrite |
Pyrite |
— |
~1.81–1.83 |
4.95–5.10 |
6–6.5 |
Isotropic |
None |
Coating possible |
Metallic luster |
| 44 |
Quartz |
Quartz |
— |
1.544–1.553 |
2.65–2.66 |
7 |
Uniaxial (+) |
~0.009 |
Heat, irradiation |
Major gem mineral |
| 45 |
Rhodochrosite |
Rhodochrosite |
— |
1.600–1.820 |
3.45–3.70 |
3.5–4 |
Uniaxial (−) |
~0.200 |
— |
Carbonate mineral |
| 46 |
Rhodonite |
Rhodonite |
— |
1.716–1.740 |
3.40–3.70 |
5.5–6.5 |
Triclinic / Biaxial |
Variable |
— |
Mn-bearing |
| 47 |
Ruby |
Corundum |
Ruby |
1.762–1.770 |
3.97–4.05 |
9 |
Uniaxial (−) |
~0.008 |
Heat, flux, diffusion, filling |
Cr-bearing corundum |
| 48 |
Sapphire |
Corundum |
Sapphire |
1.762–1.770 |
3.97–4.05 |
9 |
Uniaxial (−) |
~0.008 |
Heat, diffusion, filling |
Non-red gem corundum |
| 49 |
Scapolite |
Scapolite Group |
Various |
1.540–1.590 |
2.50–2.80 |
5.5–6 |
Uniaxial / Biaxial |
Variable |
Heat possible |
Composition-dependent |
| 50 |
Serpentine |
Serpentine Group |
Various |
1.560–1.580 |
2.44–2.62 |
2.5–5.5 |
Biaxial |
Variable |
Dyeing, impregnation |
Several polymorphs |
| 51 |
Sillimanite |
Sillimanite |
— |
1.654–1.680 |
3.23–3.25 |
6.5–7.5 |
Biaxial (+) |
~0.011 |
— |
Polymorph of Al₂SiO₅ |
| 52 |
Smithsonite |
Smithsonite |
— |
1.621–1.849 |
4.30–4.50 |
4–4.5 |
Uniaxial (−) |
Very high |
Dyeing possible |
Carbonate |
| 53 |
Sodalite |
Sodalite |
— |
1.483–1.487 |
2.14–2.40 |
5.5–6 |
Isotropic |
None |
Dyeing possible |
Often confused with Lapis |
| 54 |
Spessartine |
Garnet |
Spessartine |
1.790–1.810 |
4.12–4.20 |
7–7.5 |
Isotropic |
None |
Heat possible |
Mn-rich garnet |
| 55 |
Spinel |
Spinel |
Various |
1.712–1.762 |
3.54–3.63 |
8 |
Isotropic |
None |
Heat, diffusion possible |
Cubic |
| 56 |
Sugilite |
Sugilite |
— |
1.610–1.620 |
2.74–2.80 |
5.5–6.5 |
Uniaxial / Biaxial |
Variable |
Dyeing possible |
Purple mineral |
| 57 |
Tanzanite |
Zoisite |
Tanzanite |
1.691–1.700 |
3.35–3.56 |
6–7 |
Biaxial |
~0.009 |
Heat |
Usually heat-treated |
| 58 |
Tiger’s Eye |
Quartz |
Tiger’s Eye |
1.544–1.553 |
2.64–2.71 |
6.5–7 |
Uniaxial (+) |
~0.009 |
Dyeing possible |
Chatoyancy |
| 59 |
Topaz |
Topaz |
— |
1.606–1.634 |
3.49–3.57 |
8 |
Biaxial (+) |
~0.008–0.010 |
Irradiation, heat |
Perfect basal cleavage |
| 60 |
Tourmaline |
Tourmaline Group |
Various |
1.614–1.666 |
3.00–3.26 |
7–7.5 |
Uniaxial (−) |
~0.014–0.040 |
Heat, irradiation possible |
Strong pleochroism |
| 61 |
Tsavorite |
Grossular |
Tsavorite |
1.740–1.770 |
3.61–3.68 |
7–7.5 |
Isotropic |
None |
Usually none |
Green Grossular |
| 62 |
Turquoise |
Turquoise |
— |
1.610–1.650 |
2.40–2.90 |
5–6 |
Aggregate / cryptocrystalline |
Variable |
Wax, stabilization, dye |
Porous material |
| 63 |
Unakite |
Rock |
Unakite |
~1.53–1.57 |
2.60–2.90 |
6–7 |
Aggregate |
— |
— |
Epidote + feldspar + quartz |
| 64 |
Variscite |
Variscite |
— |
1.550–1.600 |
2.55–2.61 |
3.5–4.5 |
Biaxial |
Variable |
Dyeing possible |
Phosphate mineral |
| 65 |
Vesuvianite |
Vesuvianite |
— |
1.700–1.750 |
3.32–3.45 |
6.5 |
Uniaxial / Biaxial |
Variable |
Heat possible |
Idocrase |
| 66 |
Wollastonite |
Wollastonite |
— |
1.620–1.635 |
2.84–2.92 |
4.5–5 |
Biaxial |
~0.015 |
— |
Calcium silicate |
| 67 |
Xenotime |
Xenotime-(Y) |
— |
1.720–1.815 |
4.40–4.60 |
4–5 |
Biaxial (+) |
Variable |
— |
Rare phosphate |
| 68 |
Yellow Sapphire |
Corundum |
Yellow Sapphire |
1.762–1.770 |
3.97–4.05 |
9 |
Uniaxial (−) |
~0.008 |
Heat, diffusion |
Fe-bearing corundum |
| 69 |
Zircon |
Zircon |
Zircon |
1.810–2.024 |
3.90–4.73 |
6.5–7.5 |
Uniaxial (+) |
~0.059 |
Heat |
High/low/intermediate type |
| 70 |
Zoisite |
Zoisite |
— |
1.690–1.700 |
3.10–3.38 |
6–7 |
Biaxial (+) |
~0.005–0.018 |
Heat |
Tanzanite is a variety |