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 132 gems. Singly refractive and aggregate stones show an em-dash — they have no birefringence reading.

Taking this reading yourself? How to use a refractometer →

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.

Which birefringences a refractometer can measure Which birefringences a refractometer can measure All 75 doubly refractive entries, by birefringence on a log scale. A refractometer measures birefringence by reading both shadow edges — so it can only measure the stones whose two edges both sit on its scale. both edges on the scale — measurable (67) high edge above RI 1.81 — not measurable (8) Sugilite 0.002 Taaffeite 0.004 Apatite 0.006 Aquamarine 0.006 Danburite 0.006 Emerald 0.006 Goshenite 0.006 Heliodor 0.006 Red Beryl 0.007 Amazonite 0.008 Color-Change Sapphire 0.008 Moonstone 0.008 Morganite 0.008 Padparadscha Sapphire 0.008 Pink Sapphire 0.008 Ruby 0.008 Sapphire 0.008 Star Ruby 0.008 Star Sapphire 0.008 Synthetic Color-Change Corundum 0.008 Topaz 0.008 White Sapphire 0.008 Yellow Sapphire 0.008 Alexandrite 0.009 Amethyst 0.009 Ametrine 0.009 Cat's Eye Chrysoberyl 0.009 Chrysoberyl 0.009 Citrine 0.009 Prasiolite 0.009 Rock Crystal 0.009 Rose Quartz 0.009 Smoky Quartz 0.009 Tanzanite 0.009 Thulite 0.009 Andalusite 0.010 Enstatite 0.010 Sunstone 0.010 Labradorite 0.011 Rainbow Moonstone 0.011 Iolite 0.012 Kornerupine 0.013 Rhodonite 0.014 Hiddenite 0.016 Kunzite 0.016 Kyanite 0.016 Phenakite 0.016 Chrome Tourmaline 0.018 Green Tourmaline 0.018 Indicolite 0.018 Paraiba Tourmaline 0.018 Rubellite 0.018 Watermelon Tourmaline 0.018 Scapolite 0.020 Tourmaline 0.020 Clinohumite 0.028 Chrome Diopside 0.030 Prehnite 0.030 Star Diopside 0.030 Variscite 0.031 Grandidierite 0.033 Peridot 0.036 Sinhalite 0.038 Larimar 0.040 Moissanite 0.043 Benitoite 0.047 Diaspore 0.048 Zircon 0.059 Cassiterite 0.096 Sphene 0.100 Calcite 0.172 Rhodochrosite 0.220 Malachite 0.254 Hematite 0.280 Cinnabar 0.351 0.001 0.003 0.01 0.03 0.1 0.3 BIREFRINGENCE (LOG SCALE) Ruby 0.008 Amethyst 0.009 Tourmaline 0.020 Peridot 0.036 Moissanite 0.043 Zircon 0.059 Sphene 0.100 Calcite 0.172 Cinnabar 0.351 67 of the 75 can be measured this way. The other 8 have their high edge above the scale's ceiling of about RI 1.81, which is set by the contact liquid — and they include three of the stones this page's own lookups list: moissanite 0.043, sphene 0.100, zircon 0.059. Of the 6 entries at 0.100 or more, 5 are out of reach. Half of all entries are at or below 0.010. All 75 doubly refractive entries of gems.json; varieties count separately, as in the chart. "Measurable" means the entry's highest refractive index is at or below RI 1.81, the reach of a standard refractometer with the common high-index contact liquid (scripts/data/instrument-limits.json, sourced). The figure says nothing about whether doubling is VISIBLE through a loupe — that depends on cut and clarity as well.

Studying for the GIA or FGA practical? Loupewise 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 — 2.905–3.256 Uniaxial (+)
Hematite 0.280 — 2.940–3.220 Uniaxial (−)
Malachite 0.254 — 1.655–1.909 Biaxial (−)
Rhodochrosite 0.220 Extreme 1.600–1.820 Uniaxial (−)
Calcite 0.172 Extreme 1.486–1.658 Uniaxial (−)
Sphene 0.100 Extreme 1.843–2.110 Biaxial (+)
Cassiterite 0.096 Extreme 1.997–2.093 Uniaxial (+)
Zircon 0.059 Extreme 1.925–1.984 Uniaxial (+)
Diaspore 0.048 Moderate 1.702–1.752 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 — 1.560–1.594 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 Weak 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 — 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 — 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 Weak 1.544–1.553 Uniaxial (+)
Cat's Eye Chrysoberyl 0.009 — 1.746–1.755 Biaxial (+)
Chrysoberyl 0.009 Weak 1.746–1.755 Biaxial (+)
Citrine 0.009 Weak 1.544–1.553 Uniaxial (+)
Prasiolite 0.009 Weak 1.544–1.553 Uniaxial (+)
Rock Crystal 0.009 Weak 1.544–1.553 Uniaxial (+)
Rose Quartz 0.009 — 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 — 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 Weak 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 Weak 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
Charoite — — 1.550–1.559 Aggregate
Chrysocolla — — 1.575–1.635 Aggregate
Chrysocolla Chalcedony — — 1.530–1.543 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 — — 2.369–2.371 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 132 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?
8 transparent species in this chart are recorded with strong or extreme facet doubling: Calcite, Cassiterite, 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  ·  Open dataset (CSV & JSON, CC BY 4.0)

Enter both refractometer readings in Loupewise and the engine computes birefringence and narrows your candidates automatically.

Try Loupewise Free →