Refractive Index Chart
Refractive index, or RI is one of the most important signatures of a gemstone. Measuring the refractive index is one of the first steps in identifying a gemstone, though some gems have similar refractive indices and additional tests are required for a definitive identification.
RI is the difference between the speed of light in a vacuum and the speed of light in the gemstone. As light passes through a gemstone, it slows down because a gemstone is denser than air. This causes the path of light to change. Refraction is the bending of light as it passes in or out of a gem. The angle of refraction in the stone determines its RI. Gemstones with a high RI are more brilliant than those with a low RI. Diamond has an RI of 2.42; quartz, has an RI of 1.54-1.55. The RI of most gems is easily measured using a simple optical instrument known as a refractometer.
Sphalerite, Diamond & Hematite - Gems with High Refractive Indices
Some gemstones are singly refractive; they have only one refractive index, but most are doubly refractive; they have two different refractive indices. When a beam of light enters a doubly refractive gem, it is split into two beams, each travelling at a different speed and on a different path through the crystal. Birefringence is a measurement of the difference between the two refractive indices in gems that are doubly refractive, and it ranges from a low of .003 to a high of .287. Very few gemstones are singly refractive; in fact, the only well-known gems with that property are diamond, spinel and garnet.
The following chart lists the refractive indices for 143 varieties of gemstones, arranged in descending order.
| Hematite | ||
 |
Refractive Index | 2.94 - 3.22 |
| Double Refraction | Yes |
|
| Birefringence | 0.287 |
|
| Diamond | ||
 |
Refractive Index | 2.417 - 2.419 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Sphalerite | ||
 |
Refractive Index | 2.368 - 2.371 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Cassiterite | ||
 |
Refractive Index | 1.997 - 2.098 |
| Double Refraction | Yes |
|
| Birefringence | 0.096 to 0.098 |
|
| Demantoid Garnet | ||
 |
Refractive Index | 1.88 - 1.94 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Melanite | ||
 |
Refractive Index | 1.88 - 1.94 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Sphene | ||
 |
Refractive Index | 1.843 - 2.11 |
| Double Refraction | Yes |
|
| Birefringence | 0.100 to 0.192 |
|
| Zircon | ||
 |
Refractive Index | 1.81 - 2.024 |
| Double Refraction | Yes |
|
| Birefringence | 0.002 to 0.059 |
|
| Spessartite Garnet | ||
 |
Refractive Index | 1.79 - 1.82 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Almandine Garnet | ||
 |
Refractive Index | 1.77 - 1.82 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Ruby | ||
 |
Refractive Index | 1.762 - 1.778 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Star Sapphire | ||
 |
Refractive Index | 1.762 - 1.778 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Color Change Sapphire | ||
 |
Refractive Index | 1.762 - 1.788 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Star Ruby | ||
 |
Refractive Index | 1.762 - 1.778 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Sapphire | ||
 |
Refractive Index | 1.762 - 1.778 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Alexandrite | ||
 |
Refractive Index | 1.746 - 1.763 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.010 |
|
| Chrysoberyl | ||
 |
Refractive Index | 1.746 - 1.763 |
| Double Refraction | Yes |
|
| Birefringence | 0.007 to 0.011 |
|
| Chrysoberyl Cat's Eye | ||
 |
Refractive Index | 1.746 - 1.763 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.010 |
|
| Mali Garnet | ||
 |
Refractive Index | 1.734 - 1.759 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Grossularite Garnet | ||
 |
Refractive Index | 1.734 - 1.759 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Tsavorite Garnet | ||
 |
Refractive Index | 1.734 - 1.759 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Color-Change Garnet | ||
 |
Refractive Index | 1.73 - 1.756 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Hessonite Garnet | ||
 |
Refractive Index | 1.73 - 1.75 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Pyrope Garnet | ||
 |
Refractive Index | 1.72 - 1.756 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Star Garnet | ||
 |
Refractive Index | 1.72 - 1.756 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Rhodolite Garnet | ||
 |
Refractive Index | 1.72 - 1.76 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Azurite | ||
 |
Refractive Index | 1.72 - 1.848 |
| Double Refraction | Yes |
|
| Birefringence | 0.108 to 0.110 |
|
| Rhodonite | ||
 |
Refractive Index | 1.716 - 1.752 |
| Double Refraction | Yes |
|
| Birefringence | 0.010 to 0.014 |
|
| Spinel | ||
 |
Refractive Index | 1.712 - 1.762 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Kyanite | ||
 |
Refractive Index | 1.71 - 1.734 |
| Double Refraction | Yes |
|
| Birefringence | 0.0015 to 0.033 |
|
| Color Change Diaspore | ||
 |
Refractive Index | 1.702 - 1.75 |
| Double Refraction | Yes |
|
| Birefringence | 0.048 |
|
| Cat's Eye Diaspore Gems | ||
 |
Refractive Index | 1.702 - 1.75 |
| Double Refraction | Yes |
|
| Birefringence | 0.048 |
|
| Idocrase | ||
 |
Refractive Index | 1.7 - 1.723 |
| Double Refraction | Yes |
|
| Birefringence | 0.002 to 0.012 |
|
| Ruby-Zoisite | ||
 |
Refractive Index | 1.691 - 1.7 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Tanzanite | ||
 |
Refractive Index | 1.691 - 1.7 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Dumortierite Quartz | ||
 |
Refractive Index | 1.678 - 1.689 |
| Double Refraction | Yes |
|
| Birefringence | 0.015 to 0.037 |
|
| Tashmarine Diopside | ||
 |
Refractive Index | 1.664 - 1.73 |
| Double Refraction | Yes |
|
| Birefringence | 0.024 to 0.031 |
|
| Star Diopside | ||
 |
Refractive Index | 1.664 - 1.73 |
| Double Refraction | Yes |
|
| Birefringence | 0.024 to 0.031 |
|
| Chrome Diopside | ||
 |
Refractive Index | 1.664 - 1.73 |
| Double Refraction | Yes |
|
| Birefringence | 0.024 to 0.031 |
|
| Spodumene | ||
 |
Refractive Index | 1.66 - 1.681 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.016 |
|
| Kunzite | ||
 |
Refractive Index | 1.66 - 1.681 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.016 |
|
| Hiddenite | ||
 |
Refractive Index | 1.66 - 1.681 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.016 |
|
| Axinite | ||
 |
Refractive Index | 1.656 - 1.704 |
| Double Refraction | Yes |
|
| Birefringence | 0.010 to 0.012 |
|
| Sillimanite Cat's Eye | ||
 |
Refractive Index | 1.655 - 1.684 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.021 |
|
| Malachite | ||
 |
Refractive Index | 1.655 - 1.909 |
| Double Refraction | Yes |
|
| Birefringence | 0.254 |
|
| Peridot | ||
 |
Refractive Index | 1.65 - 1.703 |
| Double Refraction | Yes |
|
| Birefringence | 0.036 to 0.038 |
|
| Danburite | ||
 |
Refractive Index | 1.63 - 1.636 |
| Double Refraction | Yes |
|
| Birefringence | 0.006 to 0.008 |
|
| Clinohumite | ||
 |
Refractive Index | 1.629 - 1.674 |
| Double Refraction | Yes |
|
| Birefringence | 0.029 - 0.045 |
|
| Cat's Eye Apatite | ||
 |
Refractive Index | 1.628 - 1.649 |
| Double Refraction | Yes |
|
| Birefringence | 0.002 to 0.006 |
|
| Apatite | ||
 |
Refractive Index | 1.628 - 1.649 |
| Double Refraction | Yes |
|
| Birefringence | 0.002 to 0.006 |
|
| Andalusite | ||
 |
Refractive Index | 1.627 - 1.649 |
| Double Refraction | Yes |
|
| Birefringence | 0.007 to 0.013 |
|
| Smithsonite | ||
 |
Refractive Index | 1.621 - 1.849 |
| Double Refraction | Yes |
|
| Birefringence | 0.228 |
|
| Cat's Eye Tourmaline | ||
 |
Refractive Index | 1.614 - 1.666 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.032 |
|
| Tourmaline | ||
 |
Refractive Index | 1.614 - 1.666 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.032 |
|
| Rubellite Tourmaline | ||
 |
Refractive Index | 1.614 - 1.666 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.032 |
|
| Chrome Tourmaline | ||
 |
Refractive Index | 1.614 - 1.666 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.032 |
|
| Paraiba Tourmaline | ||
 |
Refractive Index | 1.614 - 1.666 |
| Double Refraction | Yes |
|
| Birefringence | 0.014 to 0.032 |
|
| Hemimorphite | ||
 |
Refractive Index | 1.614 - 1.636 |
| Double Refraction | Yes |
|
| Birefringence | 0.022 |
|
| Prehnite | ||
 |
Refractive Index | 1.611 - 1.669 |
| Double Refraction | Yes |
|
| Birefringence | 0.0021 to 0.039 |
|
| Turquoise | ||
 |
Refractive Index | 1.61 - 1.65 |
| Double Refraction | Yes |
|
| Birefringence | 0.040 |
|
| Gaspeite | ||
 |
Refractive Index | 1.61 - 1.81 |
| Double Refraction | Yes |
|
| Birefringence | 0.22 |
|
| Imperial Topaz | ||
 |
Refractive Index | 1.609 - 1.643 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.016 |
|
| Rutile Topaz | ||
 |
Refractive Index | 1.609 - 1.643 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.016 |
|
| Mystic Topaz | ||
 |
Refractive Index | 1.609 - 1.643 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.016 |
|
| Azotic Topaz | ||
 |
Refractive Index | 1.609 - 1.643 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.016 |
|
| Topaz | ||
 |
Refractive Index | 1.609 - 1.643 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.016 |
|
| Sugilite | ||
 |
Refractive Index | 1.607 - 1.611 |
| Double Refraction | Yes |
|
| Birefringence | 0.001 to 0.004 |
|
| Jadeite | ||
 |
Refractive Index | 1.6 - 1.627 |
| Double Refraction | Yes |
|
| Birefringence | 0.027 |
|
| Nephrite Jade | ||
 |
Refractive Index | 1.6 - 1.627 |
| Double Refraction | Yes |
|
| Birefringence | 0.027 |
|
| Rhodochrosite | ||
 |
Refractive Index | 1.6 - 1.82 |
| Double Refraction | Yes |
|
| Birefringence | 0.208 to 0.220 |
|
| Larimar | ||
 |
Refractive Index | 1.595 - 1.645 |
| Double Refraction | Yes |
|
| Birefringence | 0.038 |
|
| Howlite | ||
 |
Refractive Index | 1.586 - 1.605 |
| Double Refraction | Yes |
|
| Birefringence | 0.019 |
|
| Seraphinite | ||
 |
Refractive Index | 1.576 - 1.599 |
| Double Refraction | Yes |
|
| Birefringence | 0.005 to 0.011 |
|
| Emerald | ||
 |
Refractive Index | 1.565 - 1.602 |
| Double Refraction | Yes |
|
| Birefringence | 0.006 |
|
| Cat's Eye Aquamarine | ||
 |
Refractive Index | 1.564 - 1.596 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.005 |
|
| Aquamarine | ||
 |
Refractive Index | 1.564 - 1.596 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.005 |
|
| Variscite | ||
 |
Refractive Index | 1.563 - 1.594 |
| Double Refraction | Yes |
|
| Birefringence | 0.031 |
|
| Beryl | ||
 |
Refractive Index | 1.562 - 1.602 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.010 |
|
| Goshenite | ||
 |
Refractive Index | 1.562 - 1.602 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.010 |
|
| Morganite | ||
 |
Refractive Index | 1.562 - 1.602 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.010 |
|
| Serpentine | ||
 |
Refractive Index | 1.56 - 1.571 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.014 |
|
| Labradorite | ||
 |
Refractive Index | 1.559 - 1.57 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.010 |
|
| Hambergite | ||
 |
Refractive Index | 1.553 - 1.628 |
| Double Refraction | Yes |
|
| Birefringence | 0.0072 |
|
| Verdite | ||
 |
Refractive Index | 1.552 - 1.576 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Andesine Labradorite | ||
 |
Refractive Index | 1.551 - 1.561 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Charoite | ||
 |
Refractive Index | 1.55 - 1.561 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.009 |
|
| Citrine | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Rose Quartz | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Pietersite | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Amethyst | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Onyx | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Mystic Quartz | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Quartz | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Strawberry Quartz | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Smoky Quartz | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Ametrine | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Rutile Quartz | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Aventurine | ||
 |
Refractive Index | 1.544 - 1.553 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Iolite | ||
 |
Refractive Index | 1.542 - 1.578 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 to 0.012 |
|
| Jasper | ||
 |
Refractive Index | 1.54 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Peanut Wood | ||
 |
Refractive Index | 1.54 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Cat's Eye Scapolite | ||
 |
Refractive Index | 1.54 - 1.579 |
| Double Refraction | Yes |
|
| Birefringence | 0.006 to 0.037 |
|
| Scapolite | ||
 |
Refractive Index | 1.54 - 1.579 |
| Double Refraction | Yes |
|
| Birefringence | 0.006 to 0.037 |
|
| Amber | ||
 |
Refractive Index | 1.539 - 1.545 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Tiger's Eye Matrix | ||
 |
Refractive Index | 1.534 - 1.54 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Quartz Cat's Eye | ||
 |
Refractive Index | 1.534 - 1.54 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Tiger's Eye | ||
 |
Refractive Index | 1.534 - 1.54 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Fire Agate | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Chrysoprase | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | 0.004 to 0.009 |
|
| Carnelian | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Agate Geode | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Bloodstone | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Chalcedony | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Star Rose Quartz | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | 0.009 |
|
| Fossil Coral | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Dendritic Agate | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Agate | ||
 |
Refractive Index | 1.53 - 1.54 |
| Double Refraction | Yes |
|
| Birefringence | up to 0.004 |
|
| Star Sunstone | ||
 |
Refractive Index | 1.525 - 1.548 |
| Double Refraction | Yes |
|
| Birefringence | 0.010 |
|
| Sunstone | ||
 |
Refractive Index | 1.525 - 1.548 |
| Double Refraction | Yes |
|
| Birefringence | 0.010 |
|
| Lepidolite | ||
 |
Refractive Index | 1.525 - 1.586 |
| Double Refraction | Yes |
|
| Birefringence | 0.0290 to 0.0380 |
|
| Amazonite | ||
 |
Refractive Index | 1.522 - 1.53 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Maw-Sit-Sit | ||
 |
Refractive Index | 1.52 - 1.74 |
| Double Refraction | Yes |
|
| Birefringence | 0.0150 to 0.020 |
|
| Pearl | ||
 |
Refractive Index | 1.52 - 1.69 |
| Double Refraction | Yes |
|
| Birefringence | 0.156 |
|
| Ammolite | ||
 |
Refractive Index | 1.52 - 1.68 |
| Double Refraction | Yes |
|
| Birefringence | 0.155 |
|
| Star Moonstone | ||
 |
Refractive Index | 1.518 - 1.526 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Moonstone | ||
 |
Refractive Index | 1.518 - 1.526 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Rainbow Moonstone | ||
 |
Refractive Index | 1.518 - 1.526 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Orthoclase | ||
 |
Refractive Index | 1.518 - 1.53 |
| Double Refraction | Yes |
|
| Birefringence | 0.008 |
|
| Lapis Lazuli | ||
 |
Refractive Index | 1.5 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Coral | ||
 |
Refractive Index | 1.486 - 1.658 |
| Double Refraction | Yes |
|
| Birefringence | White and red: 0.160 to 0.172 |
|
| Calcite | ||
 |
Refractive Index | 1.486 - 1.658 |
| Double Refraction | Yes |
|
| Birefringence | 0.172 |
|
| Hackmanite | ||
 |
Refractive Index | 1.48 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Sodalite | ||
 |
Refractive Index | 1.48 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Moldavite | ||
 |
Refractive Index | 1.48 - 1.54 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Chrysocolla | ||
 |
Refractive Index | 1.469 - 1.57 |
| Double Refraction | Yes |
|
| Birefringence | 0.023 to 0.040 |
|
| Snowflake Obsidian | ||
 |
Refractive Index | 1.45 - 1.55 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Obsidian | ||
 |
Refractive Index | 1.45 - 1.55 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Fluorite | ||
 |
Refractive Index | 1.434 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Fire Opal | ||
 |
Refractive Index | 1.37 - 1.52 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Boulder Opal | ||
 |
Refractive Index | 1.37 - 1.52 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Opal Doublet | ||
 |
Refractive Index | 1.37 - 1.52 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Opal | ||
 |
Refractive Index | 1.37 - 1.52 |
| Double Refraction | None |
|
| Birefringence | NA |
|
| Moss Opal | ||
 |
Refractive Index | 1.37 - 1.52 |
| Double Refraction | None |
|
| Birefringence | NA |
|
- 首次发布于: December-23-2007
- 最后更新于：: February-05-2020
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