RI, SG, Mohs hardness, optic character, and the key diagnostic feature for 63 stones. Print it or save as PDF.
Other cheat sheets: All 130 stones · GIA 20-stone
| Gem | RI | SG | Mohs | Optic | Key diagnostic feature |
|---|---|---|---|---|---|
| Alexandrite | 1.746–1.755 | 3.70–3.78 | 9 | B+ | Dramatic color change |
| Almandine Garnet | 1.770–1.830 | 3.93–4.30 | 7.0–7.5 | SR | Deep red color |
| Amber | 1.539–1.545 | 1.05–1.09 | 2.0–2.5 | SR | Extremely low SG (floats in salt water) |
| Amethyst | 1.544–1.553 | 2.63–2.65 | 7 | U+ | 'Bull's eye' optic figure |
| Andalusite | 1.629–1.649 | 3.13–3.21 | 7.0–7.5 | B− | Striking trichroism: green / red-brown / yellow-orange, often visible to naked eye |
| Apatite | 1.628–1.649 | 3.17–3.23 | 5 | U− | Hardness exactly 5.0 (Mohs reference mineral) — scratched by a knife or steel file |
| Aquamarine | 1.577–1.583 | 2.68–2.78 | 7.5–8.0 | U− | Low RI and SG |
| Black Opal | 1.440–1.460 | 2.09–2.16 | 5.5–6.5 | SR | Dark body tone (N1–N4 on GIA tone scale) with vivid play-of-color |
| Cat's Eye Chrysoberyl | 1.746–1.755 | 3.70–3.78 | 9 | B+ | 'Milk and honey' effect: tilting the stone under a single point light reveals one half whitish ('milk') and one half gold/yellow ('honey') — unique to chrysoberyl among chatoyant gems |
| Chalcedony | 1.530–1.543 | 2.58–2.64 | 6.5–7.0 | AGG | Microcrystalline quartz aggregate — RI ~1.535 lower than macrocrystalline quartz (1.544–1.553) |
| Chrome Diopside | 1.664–1.730 | 3.22–3.38 | 5.5–6.5 | B+ | Chelsea filter red — chromium coloring (confirms Cr; does not distinguish from emerald without RI) |
| Chrome Tourmaline | 1.624–1.660 | 3.00–3.20 | 7.0–7.5 | U− | Chelsea filter RED — chromium coloring causes strong red reaction, unlike Fe-colored verdelite |
| Chrysoberyl | 1.746–1.755 | 3.70–3.78 | 9 | B+ | High hardness of 8.5 |
| Citrine | 1.544–1.553 | 2.63–2.65 | 7 | U+ | 'Bull's eye' optic figure |
| Color-Change Sapphire | 1.762–1.770 | 3.99–4.01 | 9 | U− | RI 1.762 — higher than alexandrite (1.746) — primary physical separator |
| Coral | 1.486–1.658 | 2.60–2.70 | 3.0–4.0 | AGG | Organic origin (skeletal material) |
| Cubic Zirconia | 2.150–2.180 | 5.60–6.00 | 8.0–8.5 | SR | Very high SG (5.6–6.0) — heaviest common gem material; dramatically heavier than any natural simulant |
| Demantoid Garnet | 1.880–1.895 | 3.82–3.88 | 6.5–7.0 | SR | Dispersion higher than diamond |
| Diamond | 2.417 | 3.50–3.53 | 10 | SR | Adamantine luster |
| Emerald | 1.565–1.602 | 2.67–2.78 | 7.5–8.0 | U− | Shows red through Chelsea filter |
| Fire Opal | 1.370–1.470 | 1.98–2.20 | 5.5–6.5 | SR | Orange-red body color with no play-of-color (typically) |
| Fluorite | 1.432–1.436 | 3.17–3.19 | 4 | SR | Low hardness (4) |
| Goshenite | 1.577–1.583 | 2.68–2.80 | 7.5–8.0 | U− | RI 1.577–1.583 clearly lower than white sapphire (1.762) and white topaz (1.619–1.627) |
| Green Tourmaline | 1.616–1.650 | 3.00–3.10 | 7.0–7.5 | U− | Much lower RI (1.624-1.644) than green sapphire (1.762) or tsavorite (1.740) |
| Grossular Garnet | 1.734–1.759 | 3.57–3.73 | 6.5–7.5 | SR | Colorless (leuco) to delicate mint green — paler, softer green than tsavorite (which is rich saturated green) |
| Heliodor | 1.568–1.580 | 2.68–2.74 | 7.5–8.0 | U− | Beryl RI and SG — separates from all yellow simulants |
| Hessonite Garnet | 1.730–1.760 | 3.59–3.65 | 7.0–7.5 | SR | Treacly or roiled internal appearance |
| Hiddenite | 1.660–1.676 | 3.15–3.21 | 6.5–7.0 | B+ | Perfect cleavage in two directions — chips easily along cleavage planes |
| Indicolite | 1.624–1.644 | 3.02–3.10 | 7.0–7.5 | U− | Strong dichroism — dark blue vs. light blue/colorless when rotated |
| Iolite | 1.535–1.547 | 2.57–2.66 | 7.0–7.5 | B− | Extreme pleochroism |
| Jadeite | 1.654–1.688 | 3.24–3.43 | 6.5–7.0 | AGG | Interlocking blocky granular texture (orange-peel surface on polished stones) |
| Jet | 1.640–1.680 | 1.10–1.40 | 2.5–4.0 | SR | Extremely low SG 1.10–1.40 — nearly floats in saturated salt water; noticeably light in hand |
| Kunzite | 1.660–1.676 | 3.15–3.21 | 6.5–7.0 | B+ | Strong pleochroism |
| Kyanite | 1.712–1.734 | 3.53–3.68 | 4.5–7.0 | B− | Variable hardness by direction — 4.5 along crystal length, 6.5–7.0 across (unique among gemstones) |
| Lapis Lazuli | 1.500–1.670 | 2.70–2.90 | 5.0–6.0 | AGG | Intense blue color |
| Malachite | 1.655–1.909 | 3.60–4.05 | 3.5–4.0 | B− | Concentric banded green patterns — swirling bull's-eye and wavy bands are the primary visual identifier |
| Morganite | 1.572–1.600 | 2.71–2.85 | 7.5–8.0 | U− | Higher RI and SG than other beryls |
| Nephrite | 1.600–1.627 | 2.90–3.03 | 6.0–6.5 | AGG | Fibrous, felted texture |
| Opal | 1.370–1.470 | 1.98–2.25 | 5.5–6.5 | SR | Play-of-color |
| Peridot | 1.654–1.690 | 3.27–3.48 | 6.5–7.0 | B+ | Very strong facet doubling |
| Pink Sapphire | 1.762–1.770 | 3.98–4.01 | 9 | U− | Strong red LW fluorescence (especially Myanmar material) — stronger than rubellite |
| Prehnite | 1.611–1.665 | 2.82–2.94 | 6.0–6.5 | B+ | Pale apple-green to yellow-green color typical |
| Pyrope Garnet | 1.730–1.760 | 3.62–3.87 | 7.0–7.5 | SR | Blood-red color |
| Rhodochrosite | 1.600–1.820 | 3.40–3.70 | 3.5–4.0 | U− | Extreme birefringence 0.220 — back facets visibly doubled even to the naked eye |
| Rhodolite Garnet | 1.740–1.770 | 3.74–3.94 | 7.0–7.5 | SR | Distinctive purplish-red to raspberry red color |
| Rhodonite | 1.716–1.752 | 3.57–3.76 | 5.5–6.5 | B+ | Pink to red color |
| Rose Quartz | 1.544–1.553 | 2.63–2.65 | 7 | U+ | Typically translucent to opaque |
| Rubellite | 1.624–1.644 | 3.02–3.10 | 7.0–7.5 | U− | Deep saturated red-pink stable under incandescent and daylight illumination |
| Ruby | 1.762–1.770 | 3.97–4.05 | 9 | U− | Strong red fluorescence (LW) |
| Sapphire | 1.762–1.770 | 3.95–4.03 | 9 | U− | Strong dichroism |
| Scapolite | 1.540–1.572 | 2.50–2.74 | 6.0–6.5 | U− | Strong orange LW and SW fluorescence — diagnostically useful, shared by few other gems |
| Serpentine | 1.560–1.571 | 2.44–2.62 | 3.0–4.0 | AGG | RI 1.560–1.571 — dramatically lower than jadeite (1.654–1.688) and nephrite (1.600–1.627) |
| Sinhalite | 1.665–1.712 | 3.47–3.50 | 6.5–7.0 | B− | Diagnostic spectroscope absorption bands at 452, 475, and 493 nm — essentially unique to sinhalite |
| Sodalite | 1.483–1.487 | 2.14–2.40 | 5.5–6.0 | AGG | Hackmanite variety shows strong orange LW fluorescence (tenebrescence); plain sodalite is inert to LW UV — lapis lazuli shows only weak orange LW |
| Spessartite Garnet | 1.790–1.815 | 4.12–4.18 | 7.0–7.5 | SR | Bright orange color |
| Sphene | 1.843–2.110 | 3.45–3.55 | 5.0–5.5 | B+ | Extreme dispersion (fire) |
| Spinel | 1.712–1.736 | 3.57–3.63 | 7.5–8.0 | SR | Singly refractive |
| Tanzanite | 1.691–1.700 | 3.35–3.38 | 6.0–7.0 | B+ | Extreme trichroism in heated (commercial) material: a-axis blue-violet, b-axis purple, c-axis green-yellow; unheated material shows brownish-red on one axis |
| Topaz | 1.609–1.643 | 3.49–3.57 | 8 | B+ | High SG for its RI range |
| Tourmaline | 1.624–1.644 | 3.01–3.26 | 7.0–7.5 | U− | Strong pleochroism |
| Tsavorite Garnet | 1.730–1.760 | 3.59–3.65 | 7.0–7.5 | SR | Bright, intense green color |
| Turquoise | 1.610–1.650 | 2.60–2.90 | 5.0–6.0 | AGG | Opaque with waxy luster |
| Zircon | 1.925–1.984 | 4.60–4.80 | 8 | U+ | Extreme facet doubling |
Optic: SR = singly refractive · U = uniaxial · B = biaxial · AGG = aggregate · +/− = optic sign. Values are typical ranges; individual stones vary. Indicators, not certifications.