This table shows gemstones arranged by their refractive index, from low to high. It’s a handy guide to help narrow down what the gem might be.
Once you have the RI, then narrow down further with birefringence, optical character, and specific gravity.
Just remember, RI alone isn’t enough, use it together with other clues like color, UV reaction, spectroscope patterns, inclusions, to get a reliable identification.
| Gemstone | Refractive Index | Birefringence | Optical Character | Specific Gravity |
|---|---|---|---|---|
| Opal | 1.40 - 1.46 | n/a | I | 2.00 - 2.20 |
| Fluorite | 1.43 - 1.44 | n/a | I | 3.00 - 3.20 |
| Sodalite | 1.48 approx. | n/a | - | 2.30 approx. |
| Calcite varieties | 1.48 - 1.66 | 0.172 | U- | 2.58 - 2.75 |
| Lapis Lazuli | 1.50 approx. | n/a | opaque | 2.70 - 2.90 |
| Natural Glass | 1.50 approx. | n/a | I (ADR) | 2.40 approx. |
| Paste / artificial glass | 1.50 - 1.70 | n/a | I (ADR) | 2.00 - 4.20 |
| Gypsum varieties | 1.52 - 1.53 | n/a | B+ | 2.30 approx. |
| Feldspar varieties | 1.52 - 1.57 | 0.004 - 0.009 | B+/- | 2.56 - 2.75 |
| Quartz, polycrystalline | 1.53 - 1.55 | n/a | polycr. Anisotropic | 2.60 approx. |
| Ivory, dentine | 1.53 - 1.57 | n/a | opaque | 1.70 - 2.00 |
| Amber | 1.54 approx. | n/a | I (ADR) | 1.05 - 1.10 |
| Ivory, vegetable | 1.54 approx. | n/a | opaque | 1.40 approx. |
| Quartz, crystalline | 1.54 - 1.56 | 0.009 | U+ | 2.65 approx. |
| Scapolite | 1.54 - 1.58 | 0.009 - 0.026 | U- | 2.50 - 2.74 |
| Iolite | 1.54 - 1.56 | 0.008 - 0.012 | B- | 2.57 - 2.61 |
| Steatite | 1.55 approx. | n/a | polycr. anisotropic | 2.70 - 2.80 |
| Tortoiseshell | 1.55 approx. | n/a | I (ADR) | 1.29 |
| Serpentine | 1.56 approx. | n/a | polycr. anisotropic | 2.60 approx. |
| Beryl varieties | 1.56 - 1.60 | 0.003 - 0.010 | U- | 2.65 - 2.80 |
| Grandidierite | 1.58 - 1.64 | 0.037 - 0.039 | B- | 2.85 - 3.00 |
| Rhodochrosite | 1.59 - 1.82 | 0.22 | U- / also poly | 3.50 - 3.70 |
| Topaz | 1.61 - 1.64 | 0.008 - 0.010 | B+ | 3.50 - 3.60 |
| Prehnite | 1.61 - 1.67 | 0.020 - 0.033 | B+ | 2.80 - 2.95 |
| Nephrite Jade | 1.62 approx. | n/a | - | 2.80 - 3.10 |
| Turquoise | 1.62 approx. | n/a | - | 2.60 - 2.90 |
| Tourmaline | 1.62 - 1.65 | 0.014 - 0.021 | U- | 3.00 - 3.10 |
| Andalusite | 1.63 - 1.64 | 0.007 - 0.013 | B- | 3.15 - 3.20 |
| Apatite | 1.63 - 1.64 | 0.002 - 0.006 | U- | 3.17 - 3.23 |
| Peridot | 1.65 - 1.69 | 0.036 | B+/- | 3.32 - 3.37 |
| Jadeite Jade | 1.66 approx. | n/a | polycr. anisotropic | 3.30 - 3.36 |
| Jet | 1.66 approx. | n/a | opaque | 1.30 approx. |
| Spodumene | 1.66 - 1.68 | 0.015 - 0.016 | B+ | 3.17 - 3.19 |
| Diopside | 1.67 - 1.70 | 0.024 - 0.030 | B+ | 3.26 - 3.32 |
| Sinhalite | 1.67 - 1.71 | 0.038 | B- | 3.47 - 3.50 |
| Tanzanite | 1.69 - 1.70 | 0.006 - 0.013 | B+ | 3.15 - 3.38 |
| Hydrogrossular Garnet | 1.70 - 1.73 | n/a | I (ADR) | 3.30 - 3.60 |
| Hessonite Garnet | 1.70 - 1.75 | n/a | I (ADR) | 3.40 - 3.80 |
| Diaspore | 1.702 - 1.75 | 0.048 | B+ | 3.30 - 3.39 |
| Kyanite | 1.71 - 1.73 | 0.017 | B- | 3.60 - 3.70 |
| Spinel | 1.71 - 1.74 | n/a | I (ADR) | 3.58 - 3.61 |
| Rhodonite | 1.72 approx. | n/a | opaque, B+ | 3.60 - 3.70 |
| Synthetic Spinel | 1.72 - 1.73 | n/a | I (ADR) | 3.61 - 3.67 |
| Pyrope Garnet | 1.72 - 1.76 | n/a | I (ADR) | 3.70 - 3.80 |
| Tsavorite Garnet | 1.73 - 1.75 | n/a | I (ADR) | 3.40 - 3.80 |
| Epidote | 1.73 - 1.77 | 0.019 - 0.045 | B- | 3.38 - 3.49 |
| Chrysoberyl | 1.74 - 1.76 | 0.008 - 0.010 | B+ | 3.71 - 3.75 |
| Rhodolite Garnet | 1.75 - 1.78 | n/a | I (ADR) | 3.80 - 3.95 |
| Corundum | 1.76 - 1.78 | 0.008 - 0.009 | U- | 3.80 - 4.05 |
| Almandine Garnet | 1.76 - 1.81 | n/a | I (ADR) | 3.80 - 4.20 |
| Zircon | 1.78 - 1.99 | up to 0.059 | U+ | 3.90 - 4.80 |
| Spessartite Garnet | 1.79 - 1.82 | n/a | I (ADR) | 4.12 - 4.20 |
| YAG | 1.83 approx. | n/a | - | 4.60 approx. |
| Malachite | 1.85 approx. | n/a | opaque | 3.60 - 4.00 |
| Sphene / Titanite | 1.88 - 2.05 | 0.105 - 0.135 | B+ | 3.40 - 3.60 |
| Demantoid Garnet | 1.89 approx. | n/a | I | 3.82 - 3.85 |
| Cubic Zirconia CZ | 2.17 approx. | n/a | I | 5.60 - 6.00 |
| Diamond | 2.42 | n/a | I | 3.52 |
| Synthetic moissanite | 2.65 - 2.69 | 0.043 | U | 3.22 |