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.

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 | ||
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Refractive Index | 2.94 - 3.22 |
Double Refraction | Yes |
|
Birefringence | 0.287 |
Diamond | ||
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Refractive Index | 2.417 - 2.419 |
Double Refraction | None |
|
Birefringence | NA |
Sphalerite | ||
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Refractive Index | 2.368 - 2.371 |
Double Refraction | None |
|
Birefringence | NA |
Cassiterite | ||
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Refractive Index | 1.997 - 2.098 |
Double Refraction | Yes |
|
Birefringence | 0.096 to 0.098 |
Demantoid Garnet | ||
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Refractive Index | 1.88 - 1.94 |
Double Refraction | None |
|
Birefringence | NA |
Melanite | ||
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Refractive Index | 1.88 - 1.94 |
Double Refraction | None |
|
Birefringence | NA |
Sphene | ||
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Refractive Index | 1.843 - 2.11 |
Double Refraction | Yes |
|
Birefringence | 0.100 to 0.192 |
Zircon | ||
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Refractive Index | 1.81 - 2.024 |
Double Refraction | Yes |
|
Birefringence | 0.002 to 0.059 |
Spessartite Garnet | ||
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Refractive Index | 1.79 - 1.82 |
Double Refraction | None |
|
Birefringence | NA |
Almandine Garnet | ||
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Refractive Index | 1.77 - 1.82 |
Double Refraction | None |
|
Birefringence | NA |
Ruby | ||
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Refractive Index | 1.762 - 1.778 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Star Sapphire | ||
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Refractive Index | 1.762 - 1.778 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Color Change Sapphire | ||
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Refractive Index | 1.762 - 1.788 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Star Ruby | ||
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Refractive Index | 1.762 - 1.778 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Sapphire | ||
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Refractive Index | 1.762 - 1.778 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Alexandrite | ||
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Refractive Index | 1.746 - 1.763 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.010 |
Chrysoberyl | ||
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Refractive Index | 1.746 - 1.763 |
Double Refraction | Yes |
|
Birefringence | 0.007 to 0.011 |
Chrysoberyl Cat's Eye | ||
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Refractive Index | 1.746 - 1.763 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.010 |
Mali Garnet | ||
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Refractive Index | 1.734 - 1.759 |
Double Refraction | None |
|
Birefringence | NA |
Grossularite Garnet | ||
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Refractive Index | 1.734 - 1.759 |
Double Refraction | None |
|
Birefringence | NA |
Tsavorite Garnet | ||
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Refractive Index | 1.734 - 1.759 |
Double Refraction | None |
|
Birefringence | NA |
Color-Change Garnet | ||
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Refractive Index | 1.73 - 1.756 |
Double Refraction | None |
|
Birefringence | NA |
Hessonite Garnet | ||
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Refractive Index | 1.73 - 1.75 |
Double Refraction | None |
|
Birefringence | NA |
Pyrope Garnet | ||
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Refractive Index | 1.72 - 1.756 |
Double Refraction | None |
|
Birefringence | NA |
Star Garnet | ||
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Refractive Index | 1.72 - 1.756 |
Double Refraction | None |
|
Birefringence | NA |
Rhodolite Garnet | ||
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Refractive Index | 1.72 - 1.76 |
Double Refraction | None |
|
Birefringence | NA |
Azurite | ||
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Refractive Index | 1.72 - 1.848 |
Double Refraction | Yes |
|
Birefringence | 0.108 to 0.110 |
Rhodonite | ||
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Refractive Index | 1.716 - 1.752 |
Double Refraction | Yes |
|
Birefringence | 0.010 to 0.014 |
Spinel | ||
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Refractive Index | 1.712 - 1.762 |
Double Refraction | None |
|
Birefringence | NA |
Kyanite | ||
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Refractive Index | 1.71 - 1.734 |
Double Refraction | Yes |
|
Birefringence | 0.0015 to 0.033 |
Color Change Diaspore | ||
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Refractive Index | 1.702 - 1.75 |
Double Refraction | Yes |
|
Birefringence | 0.048 |
Cat's Eye Diaspore Gems | ||
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Refractive Index | 1.702 - 1.75 |
Double Refraction | Yes |
|
Birefringence | 0.048 |
Idocrase | ||
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Refractive Index | 1.7 - 1.723 |
Double Refraction | Yes |
|
Birefringence | 0.002 to 0.012 |
Ruby-Zoisite | ||
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Refractive Index | 1.691 - 1.7 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Tanzanite | ||
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Refractive Index | 1.691 - 1.7 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Dumortierite Quartz | ||
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Refractive Index | 1.678 - 1.689 |
Double Refraction | Yes |
|
Birefringence | 0.015 to 0.037 |
Tashmarine Diopside | ||
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Refractive Index | 1.664 - 1.73 |
Double Refraction | Yes |
|
Birefringence | 0.024 to 0.031 |
Star Diopside | ||
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Refractive Index | 1.664 - 1.73 |
Double Refraction | Yes |
|
Birefringence | 0.024 to 0.031 |
Chrome Diopside | ||
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Refractive Index | 1.664 - 1.73 |
Double Refraction | Yes |
|
Birefringence | 0.024 to 0.031 |
Spodumene | ||
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Refractive Index | 1.66 - 1.681 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.016 |
Kunzite | ||
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Refractive Index | 1.66 - 1.681 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.016 |
Hiddenite | ||
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Refractive Index | 1.66 - 1.681 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.016 |
Axinite | ||
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Refractive Index | 1.656 - 1.704 |
Double Refraction | Yes |
|
Birefringence | 0.010 to 0.012 |
Sillimanite Cat's Eye | ||
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Refractive Index | 1.655 - 1.684 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.021 |
Malachite | ||
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Refractive Index | 1.655 - 1.909 |
Double Refraction | Yes |
|
Birefringence | 0.254 |
Peridot | ||
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Refractive Index | 1.65 - 1.703 |
Double Refraction | Yes |
|
Birefringence | 0.036 to 0.038 |
Danburite | ||
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Refractive Index | 1.63 - 1.636 |
Double Refraction | Yes |
|
Birefringence | 0.006 to 0.008 |
Clinohumite | ||
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Refractive Index | 1.629 - 1.674 |
Double Refraction | Yes |
|
Birefringence | 0.029 - 0.045 |
Cat's Eye Apatite | ||
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Refractive Index | 1.628 - 1.649 |
Double Refraction | Yes |
|
Birefringence | 0.002 to 0.006 |
Apatite | ||
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Refractive Index | 1.628 - 1.649 |
Double Refraction | Yes |
|
Birefringence | 0.002 to 0.006 |
Andalusite | ||
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Refractive Index | 1.627 - 1.649 |
Double Refraction | Yes |
|
Birefringence | 0.007 to 0.013 |
Smithsonite | ||
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Refractive Index | 1.621 - 1.849 |
Double Refraction | Yes |
|
Birefringence | 0.228 |
Cat's Eye Tourmaline | ||
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Refractive Index | 1.614 - 1.666 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.032 |
Tourmaline | ||
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Refractive Index | 1.614 - 1.666 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.032 |
Rubellite Tourmaline | ||
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Refractive Index | 1.614 - 1.666 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.032 |
Chrome Tourmaline | ||
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Refractive Index | 1.614 - 1.666 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.032 |
Paraiba Tourmaline | ||
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Refractive Index | 1.614 - 1.666 |
Double Refraction | Yes |
|
Birefringence | 0.014 to 0.032 |
Hemimorphite | ||
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Refractive Index | 1.614 - 1.636 |
Double Refraction | Yes |
|
Birefringence | 0.022 |
Prehnite | ||
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Refractive Index | 1.611 - 1.669 |
Double Refraction | Yes |
|
Birefringence | 0.0021 to 0.039 |
Turquoise | ||
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Refractive Index | 1.61 - 1.65 |
Double Refraction | Yes |
|
Birefringence | 0.040 |
Gaspeite | ||
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Refractive Index | 1.61 - 1.81 |
Double Refraction | Yes |
|
Birefringence | 0.22 |
Imperial Topaz | ||
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Refractive Index | 1.609 - 1.643 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.016 |
Rutile Topaz | ||
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Refractive Index | 1.609 - 1.643 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.016 |
Mystic Topaz | ||
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Refractive Index | 1.609 - 1.643 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.016 |
Azotic Topaz | ||
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Refractive Index | 1.609 - 1.643 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.016 |
Topaz | ||
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Refractive Index | 1.609 - 1.643 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.016 |
Sugilite | ||
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Refractive Index | 1.607 - 1.611 |
Double Refraction | Yes |
|
Birefringence | 0.001 to 0.004 |
Jadeite | ||
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Refractive Index | 1.6 - 1.627 |
Double Refraction | Yes |
|
Birefringence | 0.027 |
Nephrite Jade | ||
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Refractive Index | 1.6 - 1.627 |
Double Refraction | Yes |
|
Birefringence | 0.027 |
Rhodochrosite | ||
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Refractive Index | 1.6 - 1.82 |
Double Refraction | Yes |
|
Birefringence | 0.208 to 0.220 |
Larimar | ||
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Refractive Index | 1.595 - 1.645 |
Double Refraction | Yes |
|
Birefringence | 0.038 |
Howlite | ||
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Refractive Index | 1.586 - 1.605 |
Double Refraction | Yes |
|
Birefringence | 0.019 |
Seraphinite | ||
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Refractive Index | 1.576 - 1.599 |
Double Refraction | Yes |
|
Birefringence | 0.005 to 0.011 |
Emerald | ||
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Refractive Index | 1.565 - 1.602 |
Double Refraction | Yes |
|
Birefringence | 0.006 |
Cat's Eye Aquamarine | ||
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Refractive Index | 1.564 - 1.596 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.005 |
Aquamarine | ||
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Refractive Index | 1.564 - 1.596 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.005 |
Variscite | ||
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Refractive Index | 1.563 - 1.594 |
Double Refraction | Yes |
|
Birefringence | 0.031 |
Beryl | ||
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Refractive Index | 1.562 - 1.602 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.010 |
Goshenite | ||
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Refractive Index | 1.562 - 1.602 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.010 |
Morganite | ||
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Refractive Index | 1.562 - 1.602 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.010 |
Serpentine | ||
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Refractive Index | 1.56 - 1.571 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.014 |
Labradorite | ||
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Refractive Index | 1.559 - 1.57 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.010 |
Hambergite | ||
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Refractive Index | 1.553 - 1.628 |
Double Refraction | Yes |
|
Birefringence | 0.0072 |
Verdite | ||
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Refractive Index | 1.552 - 1.576 |
Double Refraction | None |
|
Birefringence | NA |
Andesine Labradorite | ||
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Refractive Index | 1.551 - 1.561 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Charoite | ||
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Refractive Index | 1.55 - 1.561 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.009 |
Citrine | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Rose Quartz | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Pietersite | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Amethyst | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Onyx | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Mystic Quartz | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Quartz | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Strawberry Quartz | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Smoky Quartz | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Ametrine | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Rutile Quartz | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Aventurine | ||
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Refractive Index | 1.544 - 1.553 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Iolite | ||
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Refractive Index | 1.542 - 1.578 |
Double Refraction | Yes |
|
Birefringence | 0.008 to 0.012 |
Jasper | ||
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Refractive Index | 1.54 |
Double Refraction | None |
|
Birefringence | NA |
Peanut Wood | ||
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Refractive Index | 1.54 |
Double Refraction | None |
|
Birefringence | NA |
Cat's Eye Scapolite | ||
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Refractive Index | 1.54 - 1.579 |
Double Refraction | Yes |
|
Birefringence | 0.006 to 0.037 |
Scapolite | ||
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Refractive Index | 1.54 - 1.579 |
Double Refraction | Yes |
|
Birefringence | 0.006 to 0.037 |
Amber | ||
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Refractive Index | 1.539 - 1.545 |
Double Refraction | None |
|
Birefringence | NA |
Tiger's Eye Matrix | ||
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Refractive Index | 1.534 - 1.54 |
Double Refraction | None |
|
Birefringence | NA |
Quartz Cat's Eye | ||
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Refractive Index | 1.534 - 1.54 |
Double Refraction | None |
|
Birefringence | NA |
Tiger's Eye | ||
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Refractive Index | 1.534 - 1.54 |
Double Refraction | None |
|
Birefringence | NA |
Fire Agate | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Chrysoprase | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | 0.004 to 0.009 |
Carnelian | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Agate Geode | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Bloodstone | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Chalcedony | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Star Rose Quartz | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | 0.009 |
Fossil Coral | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Dendritic Agate | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Agate | ||
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Refractive Index | 1.53 - 1.54 |
Double Refraction | Yes |
|
Birefringence | up to 0.004 |
Star Sunstone | ||
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Refractive Index | 1.525 - 1.548 |
Double Refraction | Yes |
|
Birefringence | 0.010 |
Sunstone | ||
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Refractive Index | 1.525 - 1.548 |
Double Refraction | Yes |
|
Birefringence | 0.010 |
Lepidolite | ||
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Refractive Index | 1.525 - 1.586 |
Double Refraction | Yes |
|
Birefringence | 0.0290 to 0.0380 |
Amazonite | ||
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Refractive Index | 1.522 - 1.53 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Maw-Sit-Sit | ||
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Refractive Index | 1.52 - 1.74 |
Double Refraction | Yes |
|
Birefringence | 0.0150 to 0.020 |
Pearl | ||
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Refractive Index | 1.52 - 1.69 |
Double Refraction | Yes |
|
Birefringence | 0.156 |
Ammolite | ||
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Refractive Index | 1.52 - 1.68 |
Double Refraction | Yes |
|
Birefringence | 0.155 |
Star Moonstone | ||
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Refractive Index | 1.518 - 1.526 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Moonstone | ||
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Refractive Index | 1.518 - 1.526 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Rainbow Moonstone | ||
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Refractive Index | 1.518 - 1.526 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Orthoclase | ||
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Refractive Index | 1.518 - 1.53 |
Double Refraction | Yes |
|
Birefringence | 0.008 |
Lapis Lazuli | ||
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Refractive Index | 1.5 |
Double Refraction | None |
|
Birefringence | NA |
Coral | ||
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Refractive Index | 1.486 - 1.658 |
Double Refraction | Yes |
|
Birefringence | White and red: 0.160 to 0.172 |
Calcite | ||
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Refractive Index | 1.486 - 1.658 |
Double Refraction | Yes |
|
Birefringence | 0.172 |
Hackmanite | ||
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Refractive Index | 1.48 |
Double Refraction | None |
|
Birefringence | NA |
Sodalite | ||
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Refractive Index | 1.48 |
Double Refraction | None |
|
Birefringence | NA |
Moldavite | ||
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Refractive Index | 1.48 - 1.54 |
Double Refraction | None |
|
Birefringence | NA |
Chrysocolla | ||
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Refractive Index | 1.469 - 1.57 |
Double Refraction | Yes |
|
Birefringence | 0.023 to 0.040 |
Snowflake Obsidian | ||
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Refractive Index | 1.45 - 1.55 |
Double Refraction | None |
|
Birefringence | NA |
Obsidian | ||
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Refractive Index | 1.45 - 1.55 |
Double Refraction | None |
|
Birefringence | NA |
Fluorite | ||
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Refractive Index | 1.434 |
Double Refraction | None |
|
Birefringence | NA |
Fire Opal | ||
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Refractive Index | 1.37 - 1.52 |
Double Refraction | None |
|
Birefringence | NA |
Boulder Opal | ||
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Refractive Index | 1.37 - 1.52 |
Double Refraction | None |
|
Birefringence | NA |
Opal Doublet | ||
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Refractive Index | 1.37 - 1.52 |
Double Refraction | None |
|
Birefringence | NA |
Opal | ||
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Refractive Index | 1.37 - 1.52 |
Double Refraction | None |
|
Birefringence | NA |
Moss Opal | ||
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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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