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 |
