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