Birefringence of Gemstones — Reference Chart
Last updated: August 2026
Birefringence (the difference between a doubly refractive stone's two refractive indices) for 75 doubly refractive species, sorted high to low, with facet-doubling strength for all 130 gems. Singly refractive and aggregate stones show an em-dash — they have no birefringence reading.
Common birefringence lookups: Zircon 0.059 · Moissanite 0.043 · Peridot 0.036 · Sphene 0.100 · Tourmaline 0.020 · Sapphire 0.008 · Ruby 0.008 · Quartz 0.009
Birefringence is the numerical difference between the maximum and minimum refractive indices of a doubly refractive (DR) gemstone. On a refractometer it is measured by taking both shadow-edge readings and subtracting; the result is a physical constant of the species and pairs directly with the refractive index chart. Singly refractive stones (diamond, spinel, garnet) and aggregates have a single RI and no birefringence.
High birefringence has a consequence you can see with nothing more than a 10x loupe: facet doubling. Light splitting into two rays makes the back facet edges appear doubled when viewed through the table. The Facet Doubling column records how visible this is for each species — moissanite (0.043) and zircon (0.059) show it strongly, which is a classic separation from singly refractive diamond, where facet edges stay single.
For exam candidates, doubling visible at 10x is one of the fastest observations on the bench: it immediately rules out every singly refractive candidate before an instrument is picked up. Weak birefringence (0.010 and below) generally produces no visible doubling; from roughly 0.030 upward doubling becomes conspicuous in most viewing directions.
Studying for the GIA or FGA practical? GemID drills refractometer readings and birefringence calls and runs timed mock exams built around the real exam formats.
Practice exams →| Gem | Birefringence | Facet Doubling (10x) | RI Range | Optic Character |
|---|---|---|---|---|
| Cinnabar | 0.351 | Extreme | 2.905–3.256 | Uniaxial (+) |
| Hematite | 0.280 | Extreme | 2.940–3.220 | Uniaxial (−) |
| Malachite | 0.254 | — | 1.655–1.909 | Biaxial (−) |
| Rhodochrosite | 0.220 | Extreme | 1.600–1.820 | Uniaxial (−) |
| Sphene | 0.100 | Extreme | 1.843–2.110 | Biaxial (+) |
| Cassiterite | 0.096 | Extreme | 2.010–2.100 | Uniaxial (+) |
| Zircon | 0.059 | Extreme | 1.925–1.984 | Uniaxial (+) |
| Diaspore | 0.048 | Moderate | 1.685–1.752 | Biaxial (+) |
| Benitoite | 0.047 | Moderate | 1.757–1.804 | Uniaxial (+) |
| Moissanite | 0.043 | Extreme | 2.648–2.691 | Uniaxial (+) |
| Larimar | 0.040 | — | 1.595–1.640 | Biaxial (+) |
| Sinhalite | 0.038 | Strong | 1.665–1.712 | Biaxial (−) |
| Peridot | 0.036 | Extreme | 1.654–1.690 | Biaxial (+) |
| Grandidierite | 0.033 | Weak | 1.590–1.623 | Biaxial (−) |
| Variscite | 0.031 | — | 1.560–1.590 | Biaxial (−) |
| Chrome Diopside | 0.030 | Moderate | 1.664–1.730 | Biaxial (+) |
| Prehnite | 0.030 | Moderate | 1.611–1.665 | Biaxial (+) |
| Star Diopside | 0.030 | — | 1.664–1.721 | Biaxial (+) |
| Clinohumite | 0.028 | Moderate | 1.625–1.675 | Biaxial (+) |
| Scapolite | 0.020 | Moderate | 1.540–1.572 | Uniaxial (−) |
| Tourmaline | 0.020 | Moderate | 1.624–1.644 | Uniaxial (−) |
| Chrome Tourmaline | 0.018 | Weak | 1.624–1.660 | Uniaxial (−) |
| Green Tourmaline | 0.018 | — | 1.616–1.650 | Uniaxial (−) |
| Indicolite | 0.018 | Moderate | 1.624–1.644 | Uniaxial (−) |
| Paraiba Tourmaline | 0.018 | Moderate | 1.624–1.644 | Uniaxial (−) |
| Rubellite | 0.018 | Moderate | 1.624–1.644 | Uniaxial (−) |
| Watermelon Tourmaline | 0.018 | Moderate | 1.616–1.650 | Uniaxial (−) |
| Hiddenite | 0.016 | Weak | 1.660–1.676 | Biaxial (+) |
| Kunzite | 0.016 | Moderate | 1.660–1.676 | Biaxial (+) |
| Kyanite | 0.016 | Moderate | 1.712–1.734 | Biaxial (−) |
| Phenakite | 0.016 | Weak | 1.654–1.670 | Uniaxial (+) |
| Rhodonite | 0.014 | Moderate | 1.716–1.752 | Biaxial (+) |
| Kornerupine | 0.013 | Weak | 1.660–1.699 | Biaxial (−) |
| Iolite | 0.012 | Weak | 1.540–1.560 | Biaxial (−) |
| Labradorite | 0.011 | Moderate | 1.559–1.573 | Biaxial (−) |
| Rainbow Moonstone | 0.011 | Weak | 1.559–1.572 | Biaxial (−) |
| Andalusite | 0.010 | — | 1.629–1.649 | Biaxial (−) |
| Enstatite | 0.010 | — | 1.663–1.673 | Biaxial (+) |
| Sunstone | 0.010 | Weak | 1.537–1.572 | Biaxial (−) |
| Alexandrite | 0.009 | Weak | 1.746–1.755 | Biaxial (+) |
| Amethyst | 0.009 | Weak | 1.544–1.553 | Uniaxial (+) |
| Ametrine | 0.009 | — | 1.544–1.553 | Uniaxial (+) |
| Cat's Eye Chrysoberyl | 0.009 | — | 1.746–1.755 | Biaxial (+) |
| Charoite | 0.009 | — | 1.550–1.559 | Aggregate |
| Chrysoberyl | 0.009 | Weak | 1.746–1.755 | Biaxial (+) |
| Citrine | 0.009 | Weak | 1.544–1.553 | Uniaxial (+) |
| Prasiolite | 0.009 | — | 1.544–1.553 | Uniaxial (+) |
| Rock Crystal | 0.009 | Weak | 1.544–1.553 | Uniaxial (+) |
| Rose Quartz | 0.009 | Weak | 1.544–1.553 | Uniaxial (+) |
| Smoky Quartz | 0.009 | Weak | 1.544–1.553 | Uniaxial (+) |
| Tanzanite | 0.009 | Weak | 1.691–1.700 | Biaxial (+) |
| Thulite | 0.009 | — | 1.691–1.704 | Biaxial (+) |
| Amazonite | 0.008 | Weak | 1.514–1.530 | Biaxial (−) |
| Color-Change Sapphire | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Moonstone | 0.008 | — | 1.518–1.526 | Biaxial (−) |
| Morganite | 0.008 | Weak | 1.572–1.600 | Uniaxial (−) |
| Padparadscha Sapphire | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Pink Sapphire | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Ruby | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Sapphire | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Star Ruby | 0.008 | — | 1.762–1.770 | Uniaxial (−) |
| Star Sapphire | 0.008 | — | 1.762–1.770 | Uniaxial (−) |
| Synthetic Color-Change Corundum | 0.008 | — | 1.762–1.770 | Uniaxial (−) |
| Topaz | 0.008 | Weak | 1.609–1.643 | Biaxial (+) |
| White Sapphire | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Yellow Sapphire | 0.008 | Weak | 1.762–1.770 | Uniaxial (−) |
| Red Beryl | 0.007 | — | 1.564–1.574 | Uniaxial (−) |
| Apatite | 0.006 | — | 1.628–1.649 | Uniaxial (−) |
| Aquamarine | 0.006 | Weak | 1.577–1.583 | Uniaxial (−) |
| Danburite | 0.006 | — | 1.627–1.636 | Biaxial (−) |
| Emerald | 0.006 | Weak | 1.565–1.602 | Uniaxial (−) |
| Goshenite | 0.006 | — | 1.577–1.583 | Uniaxial (−) |
| Heliodor | 0.006 | Weak | 1.568–1.580 | Uniaxial (−) |
| Taaffeite | 0.004 | Weak | 1.719–1.723 | Uniaxial (−) |
| Sugilite | 0.002 | — | 1.607–1.610 | Uniaxial (−) |
| Agate | — | — | 1.530–1.543 | Aggregate |
| Almandine Garnet | — | — | 1.770–1.830 | SR |
| Amber | — | — | 1.539–1.545 | SR |
| Aventurine | — | — | 1.544–1.553 | Aggregate |
| Black Opal | — | — | 1.440–1.460 | SR |
| Black Spinel | — | — | 1.712–1.730 | SR |
| Bloodstone | — | — | 1.530–1.543 | Aggregate |
| Blue Diamond | — | — | 2.417 | SR |
| Brown Diamond | — | — | 2.417 | SR |
| Carnelian | — | — | 1.530–1.543 | Aggregate |
| Chalcedony | — | — | 1.530–1.543 | Aggregate |
| Chrysocolla | — | — | 1.460–1.630 | Aggregate |
| Chrysoprase | — | — | 1.530–1.543 | Aggregate |
| Color-Change Garnet | — | — | 1.740–1.765 | SR |
| Coral | — | — | 1.486–1.658 | Aggregate |
| Cubic Zirconia | — | — | 2.150–2.180 | SR |
| Cuprite | — | — | 2.849 | SR |
| Demantoid Garnet | — | — | 1.880–1.895 | SR |
| Diamond | — | — | 2.417 | SR |
| Fire Opal | — | — | 1.370–1.470 | SR |
| Fluorite | — | — | 1.432–1.436 | SR |
| Grossular Garnet | — | — | 1.734–1.759 | SR |
| Hackmanite | — | — | 1.483–1.487 | SR |
| Hauyne | — | — | 1.494–1.509 | SR |
| Hawk's Eye | — | — | 1.544–1.553 | Aggregate |
| Hessonite Garnet | — | — | 1.730–1.760 | SR |
| Howlite | — | — | 1.583–1.608 | Aggregate |
| Ivory | — | — | 1.535–1.540 | Aggregate |
| Jadeite | — | — | 1.654–1.688 | Aggregate |
| Jet | — | — | 1.640–1.680 | SR |
| Lapis Lazuli | — | — | 1.500–1.670 | Aggregate |
| Low-Type Zircon | — | — | 1.780–1.815 | SR |
| Malaya / Umbalite Garnet | — | — | 1.730–1.780 | SR |
| Moldavite | — | — | 1.480–1.510 | SR |
| Nephrite | — | — | 1.600–1.627 | Aggregate |
| Obsidian | — | — | 1.480–1.510 | SR |
| Onyx | — | — | 1.530–1.543 | Aggregate |
| Opal | — | — | 1.370–1.470 | SR |
| Pearl | — | — | 1.520–1.690 | Aggregate |
| Pietersite | — | — | 1.534–1.540 | Aggregate |
| Pink Diamond | — | — | 2.417 | SR |
| Pyrope Garnet | — | — | 1.730–1.760 | SR |
| Rhodolite Garnet | — | — | 1.740–1.770 | SR |
| Serpentine | — | — | 1.560–1.571 | Aggregate |
| Sodalite | — | — | 1.483–1.487 | Aggregate |
| Spessartite Garnet | — | — | 1.790–1.815 | SR |
| Sphalerite | — | — | 2.369–2.500 | SR |
| Spinel | — | — | 1.712–1.736 | SR |
| Star Garnet | — | — | 1.770–1.830 | SR |
| Synthetic Spinel | — | — | 1.725–1.728 | SR |
| Tiger's Eye | — | — | 1.544–1.553 | Aggregate |
| Tsavorite Garnet | — | — | 1.730–1.760 | SR |
| Turquoise | — | — | 1.610–1.650 | Aggregate |
| YAG | — | — | 1.833 | SR |
| Yellow Diamond | — | — | 2.417 | SR |
Click a column header to re-sort the table.
Which gemstone has the highest birefringence?
Among the 130 gems in this reference, Cinnabar has the highest birefringence at 0.351. The table ranks all 75 doubly refractive species from highest to lowest.
Which gemstones show facet doubling under a loupe?
9 species in this chart are recorded with strong or extreme facet doubling: Cassiterite, Cinnabar, Hematite, Moissanite, Peridot, Rhodochrosite, Sinhalite, Sphene, Zircon. Visible doubling at 10x immediately rules out singly refractive candidates such as diamond, spinel, and garnet.
What is the birefringence of zircon?
Zircon (high type) has a birefringence of 0.059 — its facet doubling is extreme and easily seen with a 10x loupe, a classic separation from diamond.
All instrument charts: Refractive Index · Specific Gravity · Mohs Hardness · Fluorescence · Pleochroism · Spectroscope · Optic Character · Chelsea & Hanneman Filters · Dispersion · Magnetism
See also: Full Reference Database · How to Use a Refractometer · Exam Study Guides
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