Gemopedia - Gem Identification
This reference table provides key gemological properties used for the identification of gemstones. It is designed as a practical overview, combining essential optical and physical characteristics such as refractive index, birefringence, hardness, and specific gravity.
The data presented here follows standard gemological methods and allows for quick comparison between different gemstone species and groups. While no single property is sufficient for a definitive identification, the combination of these values provides a reliable foundation for distinguishing natural gemstones.
This Gemopedia is intended as a growing resource. Detailed information about each gemstone, including treatments, inclusions, and cutting considerations will be available on dedicated pages in the future.
Look below for the column definitions.
Gem Identification Table
| Name | Group | Color(s) | RI | Birefringence | Hardness | SG | Polarization | Pleochroism | Chelsea Filter |
|---|---|---|---|---|---|---|---|---|---|
| Alexandrite | Chrysoberyl | green/red | 1.741–1.760 | 0.009 | 8.5 | 3.70–3.78 | DR | strong | red |
| Amazonite | Feldspar | green | 1.522–1.530 | 0.008 | 6–6.5 | 2.56 | DR | weak | inert |
| Amethyst | Quartz | violet | 1.544–1.553 | 0.009 | 7 | 2.65 | DR | weak | inert |
| Andalusite | Silicate | green, brown | 1.629–1.650 | 0.010 | 7.5 | 3.15 | DR | strong | inert |
| Apatite | Apatite | green, blue | 1.632–1.645 | 0.013 | 5 | 3.2 | DR | weak | inert |
| Aquamarine | Beryl | blue | 1.577–1.583 | 0.005 | 7.5–8 | 2.68–2.74 | DR | weak (blue/light) | inert |
| Azurite | Carbonate | blue | 1.73–1.84 | 0.110 | 3.5–4 | 3.7–3.9 | DR | weak | inert |
| Cat’s Eye Chrysoberyl | Chrysoberyl | yellow-green | 1.746–1.755 | 0.009 | 8.5 | 3.7 | DR | weak | inert |
| Chrysoberyl | Chrysoberyl | yellow, green | 1.745–1.754 | 0.009 | 8.5 | 3.70–3.75 | DR | weak | inert |
| Citrine | Quartz | yellow | 1.544–1.553 | 0.009 | 7 | 2.65 | DR | weak | inert |
| Diamond | Carbon | colorless, yellow, blue, pink | 2.417 | 0 | 10 | 3.52 | Isotropic | none | inert |
| Diopside | Pyroxene | green | 1.664–1.730 | 0.030 | 5.5–6.5 | 3.3 | DR | moderate | inert |
| Emerald | Beryl | green | 1.577–1.583 | 0.006 | 7.5–8 | 2.67–2.78 | DR | distinct (green/blue-green) | red |
| Fire Opal | Opal | orange, red | 1.37–1.47 | 0 | 5–6.5 | 2.1 | Amorphous | none | inert |
| Fluorite | Fluorite | purple, green | 1.433–1.435 | 0 | 4 | 3.18 | Isotropic | none | inert |
| Garnet (Almandine) | Garnet | dark red | 1.76–1.83 | 0 | 7–7.5 | 4.0–4.3 | Isotropic | none | inert |
| Garnet (Andradite) | Garnet | green, black | 1.88–1.94 | 0 | 6.5–7 | 3.8–4.1 | Isotropic | none | inert |
| Garnet (Grossular) | Garnet | green, yellow | 1.72–1.75 | 0 | 6.5–7.5 | 3.5–3.7 | Isotropic | none | inert |
| Garnet (Pyrope) | Garnet | red | 1.73–1.76 | 0 | 7–7.5 | 3.7–3.9 | Isotropic | none | inert |
| Garnet (Spessartine) | Garnet | orange | 1.79–1.82 | 0 | 7 | 4.0–4.2 | Isotropic | none | inert |
| Hematite | Hematite | metallic gray | 2.94 | 0 | 5–6 | 5.3 | Opaque | none | inert |
| Heliodor | Beryl | yellow | 1.577–1.583 | 0.005 | 7.5–8 | 2.66–2.90 | DR | weak | inert |
| Iolite | Cordierite | blue, violet | 1.542–1.578 | 0.008–0.012 | 7–7.5 | 2.6 | DR | strong | inert |
| Imperial Topaz | Topaz | orange, pink | 1.609–1.643 | 0.010 | 8 | 3.50 | DR | weak | inert |
| Jadeite | Jade | green, white | 1.660–1.680 | 0.012 | 6.5–7 | 3.3 | DR | weak | inert |
| Kyanite | Kyanite | blue | 1.712–1.734 | 0.016 | 4.5–7 | 3.6 | DR | moderate | inert |
| Labradorite | Feldspar | gray, blue flash | 1.559–1.573 | 0.008 | 6–6.5 | 2.7 | DR | weak | inert |
| Lapis Lazuli | Rock | blue | 1.50 | 0 | 5–6 | 2.7–2.9 | Aggregate | none | inert |
| Malachite | Carbonate | green | 1.65–1.91 | 0.254 | 3.5–4 | 3.6–4.0 | DR | weak | inert |
| Moonstone | Feldspar | white, blue sheen | 1.518–1.526 | 0.008 | 6–6.5 | 2.56 | DR | weak | inert |
| Morganite | Beryl | pink, peach | 1.577–1.583 | 0.005 | 7.5–8 | 2.71–2.90 | DR | weak (pink/orange) | inert |
| Nephrite | Jade | green | 1.600–1.630 | 0.020 | 6–6.5 | 2.95 | DR | weak | inert |
| Opal | Mineraloid | all colors | 1.37–1.47 | 0 | 5–6.5 | 2.1 | Amorphous | none | inert |
| Paraiba Tourmaline | Tourmaline | neon blue/green | 1.610–1.650 | 0.020 | 7–7.5 | 3.0 | DR | strong | inert |
| Peridot | Olivine | green | 1.650–1.690 | 0.036 | 6.5–7 | 3.3–3.5 | DR | strong (green/yellow) | inert |
| Quartz | Quartz | colorless, violet, yellow | 1.544–1.553 | 0.009 | 7 | 2.65 | DR | weak | inert |
| Rhodonite | Silicate | pink | 1.710–1.740 | 0.010 | 5.5–6.5 | 3.5 | DR | weak | inert |
| Rose Quartz | Quartz | pink | 1.544–1.553 | 0.009 | 7 | 2.65 | DR | weak | inert |
| Ruby | Corundum | red | 1.762–1.770 | 0.008 | 9 | 3.97–4.05 | DR | strong (red/orange) | red |
| Sapphire | Corundum | blue, yellow, pink | 1.762–1.770 | 0.008 | 9 | 3.95–4.03 | DR | weak–strong (blue/green) | inert |
| Sillimanite | Sillimanite | colorless, brown | 1.658–1.677 | 0.017 | 6.5–7.5 | 3.2 | DR | weak | inert |
| Smoky Quartz | Quartz | brown | 1.544–1.553 | 0.009 | 7 | 2.65 | DR | weak | inert |
| Spinel | Spinel | red, blue, pink | 1.718 | 0 | 8 | 3.58–3.61 | Isotropic | none | red (red stones) |
| Sunstone | Feldspar | orange, red | 1.52–1.57 | 0.008 | 6–6.5 | 2.65 | DR | weak | inert |
| Tanzanite | Zoisite | blue, violet | 1.691–1.700 | 0.008 | 6–7 | 3.35 | DR | strong (trichroic) | inert |
| Topaz | Topaz | blue, colorless, yellow | 1.609–1.643 | 0.008–0.010 | 8 | 3.49–3.57 | DR | weak | inert |
| Tourmaline | Tourmaline | all colors | 1.614–1.666 | 0.014–0.040 | 7–7.5 | 3.0–3.3 | DR | strong | variable |
| Zircon | Zircon | colorless, blue, brown | 1.810–2.024 | 0.059 | 6–7.5 | 4.6–4.7 | DR | strong | inert |
| Zoisite | Zoisite | green, pink | 1.690–1.700 | 0.008 | 6–7 | 3.35 | DR | moderate | inert |
Column Definitions
Name
The commonly used trade name of the gemstone.
Group
The mineral group or species the gemstone belongs to. Stones within the same group often share similar chemical and physical properties.
Color(s)
Typical color range observed in the gemstone. Variations may occur depending on trace elements and origin.
Refractive Index (RI)
A measure of how strongly light is bent when entering the gemstone. One of the most important properties for gemstone identification.
Birefringence
The numerical difference between the two refractive indices in double-refractive gemstones. It indicates how strongly light is split into two rays.
Hardness (Mohs)
Resistance to scratching based on the Mohs scale (1–10). This value is important for durability and wearability.
Specific Gravity (SG)
The relative density of the gemstone compared to water. Useful for distinguishing between gemstones with similar appearance.
Polarization
Indicates how the gemstone interacts with polarized light:
-
Isotropic: single refractive (no doubling)
-
DR (Doubly Refractive): splits light into two rays
-
Aggregate / Amorphous: irregular or no crystal structure
Pleochroism
The ability of a gemstone to show different colors when viewed from different directions. Strength and color combinations vary by mineral.
Chelsea Filter
A diagnostic tool used to observe color reactions under specific light wavelengths. Some gemstones show characteristic colors (e.g. red in ruby or emerald).