Dispersion of Gemstones — Fire Reference Chart

Last updated: August 2026

Dispersion values (the B–G interval) for 115 of the 132 gemstone species in this chart, sorted high to low. Dispersion is the property behind "fire" — the rainbow flashes a cut stone throws as it moves.

Common dispersion lookups: Diamond 0.044  ·  Moissanite 0.104  ·  Cubic Zirconia 0.066  ·  Zircon 0.039  ·  Sphene 0.051  ·  Demantoid Garnet 0.057  ·  Sapphire 0.018

Dispersion measures how strongly a gem material spreads white light into its spectral colors — numerically, the difference between its refractive indices at the blue (486.1 nm) and red (656.3 nm) Fraunhofer lines. In a faceted stone that spread appears as fire: the flashes of rainbow color that play across the crown as the stone, the light, or the observer moves. Cut quality controls how much of a stone's potential fire is actually displayed, but the ceiling is set by this constant.

Diamond's fire (0.044) is the benchmark, and the values around it explain a lot of bench observations: moissanite at 0.104 shows more than twice diamond's fire — often the first tell that a "diamond" is too lively, and cubic zirconia at 0.066 also overshoots it. Among colored stones, cinnabar (0.400), sphalerite (0.156), cuprite (0.155) top the chart, though strong body color can mask fire in deeply saturated material.

Dispersion is not measured directly in routine testing — it is observed. Judge fire under a single strong point light against a dark background, and weigh it alongside the measured constants: a stone whose fire is clearly out of proportion to its supposed identity deserves a refractometer reading. Species shown with a dash have no dispersion value recorded — mostly opaque and aggregate materials, where fire is not observable.

More fire than diamond, and what a refractometer says about it More fire than diamond, and what a refractometer says about it All 115 entries with a recorded dispersion, on a log scale. The page's advice for a stone with too much fire is to take a refractometer reading — but a refractometer only shows a shadow edge for an index below about RI 1.81. Above that it reads "over the limit" and gives no number. refractometer gives a reading (100) lowest index above RI 1.81 — reads only "over the limit" (15) diamond 0.044 → more fire Charoite 0.005 · RI 1.550 Fluorite 0.007 · RI 1.432 Larimar 0.010 · RI 1.595 Moldavite 0.010 · RI 1.480 Obsidian 0.010 · RI 1.480 Sugilite 0.010 · RI 1.607 Amazonite 0.012 · RI 1.514 Labradorite 0.012 · RI 1.559 Moonstone 0.012 · RI 1.518 Rainbow Moonstone 0.012 · RI 1.559 Sunstone 0.012 · RI 1.537 Thulite 0.012 · RI 1.691 Agate 0.013 · RI 1.530 Amethyst 0.013 · RI 1.544 Ametrine 0.013 · RI 1.544 Apatite 0.013 · RI 1.628 Aventurine 0.013 · RI 1.544 Bloodstone 0.013 · RI 1.530 Carnelian 0.013 · RI 1.530 Chalcedony 0.013 · RI 1.530 Chrysocolla Chalcedony 0.013 · RI 1.530 Chrysoprase 0.013 · RI 1.530 Citrine 0.013 · RI 1.544 Hawk's Eye 0.013 · RI 1.544 Onyx 0.013 · RI 1.530 Prasiolite 0.013 · RI 1.544 Rock Crystal 0.013 · RI 1.544 Rose Quartz 0.013 · RI 1.544 Smoky Quartz 0.013 · RI 1.544 Star Diopside 0.013 · RI 1.664 Tiger's Eye 0.013 · RI 1.544 Aquamarine 0.014 · RI 1.577 Emerald 0.014 · RI 1.565 Goshenite 0.014 · RI 1.577 Heliodor 0.014 · RI 1.568 Morganite 0.014 · RI 1.572 Red Beryl 0.014 · RI 1.564 Topaz 0.014 · RI 1.609 Alexandrite 0.015 · RI 1.746 Cat's Eye Chrysoberyl 0.015 · RI 1.746 Chrysoberyl 0.015 · RI 1.746 Grandidierite 0.015 · RI 1.590 Phenakite 0.015 · RI 1.654 Rhodochrosite 0.015 · RI 1.600 Andalusite 0.016 · RI 1.629 Rhodonite 0.016 · RI 1.716 Variscite 0.016 · RI 1.560 Calcite 0.017 · RI 1.486 Chrome Tourmaline 0.017 · RI 1.624 Danburite 0.017 · RI 1.627 Enstatite 0.017 · RI 1.663 Green Tourmaline 0.017 · RI 1.616 Hiddenite 0.017 · RI 1.660 Indicolite 0.017 · RI 1.624 Iolite 0.017 · RI 1.540 Kunzite 0.017 · RI 1.660 Paraiba Tourmaline 0.017 · RI 1.624 Rubellite 0.017 · RI 1.624 Scapolite 0.017 · RI 1.540 Tourmaline 0.017 · RI 1.624 Watermelon Tourmaline 0.017 · RI 1.616 Color-Change Sapphire 0.018 · RI 1.762 Hackmanite 0.018 · RI 1.483 Kornerupine 0.018 · RI 1.660 Padparadscha Sapphire 0.018 · RI 1.762 Pink Sapphire 0.018 · RI 1.762 Ruby 0.018 · RI 1.762 Sapphire 0.018 · RI 1.762 Sinhalite 0.018 · RI 1.665 Star Ruby 0.018 · RI 1.762 Star Sapphire 0.018 · RI 1.762 Synthetic Color-Change Corundum 0.018 · RI 1.762 White Sapphire 0.018 · RI 1.762 Yellow Sapphire 0.018 · RI 1.762 Hauyne 0.019 · RI 1.494 Taaffeite 0.019 · RI 1.719 Black Spinel 0.020 · RI 1.712 Chrome Diopside 0.020 · RI 1.664 Diaspore 0.020 · RI 1.702 Kyanite 0.020 · RI 1.712 Opal 0.020 · RI 1.370 Peridot 0.020 · RI 1.654 Prehnite 0.020 · RI 1.611 Spinel 0.020 · RI 1.712 Synthetic Spinel 0.020 · RI 1.725 Clinohumite 0.022 · RI 1.625 Pyrope Garnet 0.022 · RI 1.730 Malaya / Umbalite Garnet 0.023 · RI 1.730 Almandine Garnet 0.024 · RI 1.770 Star Garnet 0.024 · RI 1.770 Malachite 0.025 · RI 1.655 Color-Change Garnet 0.026 · RI 1.740 Rhodolite Garnet 0.026 · RI 1.740 Spessartite Garnet 0.027 · RI 1.790 Grossular Garnet 0.028 · RI 1.734 Hessonite Garnet 0.028 · RI 1.730 Tsavorite Garnet 0.028 · RI 1.730 YAG 0.028 · RI 1.833 Tanzanite 0.030 · RI 1.691 Low-Type Zircon 0.038 · RI 1.780 Zircon 0.039 · RI 1.925 Blue Diamond 0.044 · RI 2.417 Brown Diamond 0.044 · RI 2.417 Diamond 0.044 · RI 2.417 Pink Diamond 0.044 · RI 2.417 Yellow Diamond 0.044 · RI 2.417 Benitoite 0.046 · RI 1.757 Sphene 0.051 · RI 1.843 Demantoid Garnet 0.057 · RI 1.880 Cubic Zirconia 0.066 · RI 2.150 Cassiterite 0.071 · RI 1.997 Moissanite 0.104 · RI 2.648 Cuprite 0.155 · RI 2.849 Sphalerite 0.156 · RI 2.369 Cinnabar 0.400 · RI 2.905 0.005 0.01 0.02 0.05 0.1 0.2 0.5 DISPERSION, B–G (LOG SCALE) Sapphire 0.018 Zircon 0.039 Diamond 0.044 Sphene 0.051 Demantoid Garnet 0.057 Cubic Zirconia 0.066 Moissanite 0.104 Cinnabar 0.400 9 entries have more fire than diamond's 0.044. 8 of them read only "over the limit": cinnabar 0.400, sphalerite 0.156, cuprite 0.155, moissanite 0.104, cassiterite 0.071, cubic zirconia 0.066, demantoid garnet 0.057, sphene 0.051. Only benitoite (RI 1.757–1.804) gives a reading. Diamond itself, at RI 2.417, is over the limit too. So for a too-lively stone the refractometer mostly confirms "high index" and cannot say which of these it is. Across all 115 entries, 15 read over the limit, and 13 of the 14 at diamond's fire or above. The 115 entries of gems.json with a recorded dispersion (B–G interval); 17 with no recorded value are not drawn. Varieties count separately, as in the chart. "Over the limit" means the entry's LOWEST refractive index is above RI 1.81, the reach of a standard refractometer with the common high-index contact liquid (scripts/data/instrument-limits.json, sourced). How much fire a cut stone SHOWS also depends on cut, size and body colour; the figure draws only the constant.

Studying for the GIA or FGA practical? Loupewise drills the observations that go with the numbers — fire, doubling, luster — and runs timed mock exams built around the real exam formats.

Practice exams →
Gem Dispersion (B–G) RI Range Optic Character Hardness
Cinnabar 0.400 2.905–3.256 Uniaxial (+) 2–2.5
Sphalerite 0.156 2.369–2.371 SR 3.5–4
Cuprite 0.155 2.849 SR 3.5–4
Moissanite 0.104 2.648–2.691 Uniaxial (+) 9.25
Cassiterite 0.071 1.997–2.093 Uniaxial (+) 6–7
Cubic Zirconia 0.066 2.150–2.180 SR 8–8.5
Demantoid Garnet 0.057 1.880–1.895 SR 6.5–7
Sphene 0.051 1.843–2.110 Biaxial (+) 5–5.5
Benitoite 0.046 1.757–1.804 Uniaxial (+) 6–6.5
Blue Diamond 0.044 2.417 SR 10
Brown Diamond 0.044 2.417 SR 10
Diamond 0.044 2.417 SR 10
Pink Diamond 0.044 2.417 SR 10
Yellow Diamond 0.044 2.417 SR 10
Zircon 0.039 1.925–1.984 Uniaxial (+) 7.5
Low-Type Zircon 0.038 1.780–1.815 SR 6
Tanzanite 0.030 1.691–1.700 Biaxial (+) 6–7
Grossular Garnet 0.028 1.734–1.759 SR 6.5–7.5
Hessonite Garnet 0.028 1.730–1.760 SR 7–7.5
Tsavorite Garnet 0.028 1.730–1.760 SR 7–7.5
YAG 0.028 1.833 SR 8–8.5
Spessartite Garnet 0.027 1.790–1.815 SR 7–7.5
Color-Change Garnet 0.026 1.740–1.765 SR 7–7.5
Rhodolite Garnet 0.026 1.740–1.770 SR 7–7.5
Malachite 0.025 1.655–1.909 Biaxial (−) 3.5–4
Almandine Garnet 0.024 1.770–1.830 SR 7–7.5
Star Garnet 0.024 1.770–1.830 SR 7–7.5
Malaya / Umbalite Garnet 0.023 1.730–1.780 SR 7–7.5
Clinohumite 0.022 1.625–1.675 Biaxial (+) 6
Pyrope Garnet 0.022 1.730–1.760 SR 7–7.5
Black Spinel 0.020 1.712–1.730 SR 8
Chrome Diopside 0.020 1.664–1.730 Biaxial (+) 5.5–6.5
Diaspore 0.020 1.702–1.752 Biaxial (+) 6.5–7
Kyanite 0.020 1.712–1.734 Biaxial (−) 4.5–7
Opal 0.020 1.370–1.470 SR 5.5–6.5
Peridot 0.020 1.654–1.690 Biaxial (+) 6.5–7
Prehnite 0.020 1.611–1.665 Biaxial (+) 6–6.5
Spinel 0.020 1.712–1.736 SR 7.5–8
Synthetic Spinel 0.020 1.725–1.728 SR 8
Hauyne 0.019 1.494–1.509 SR 5.5–6
Taaffeite 0.019 1.719–1.723 Uniaxial (−) 8–8.5
Color-Change Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Hackmanite 0.018 1.483–1.487 SR 5.5–6
Kornerupine 0.018 1.660–1.699 Biaxial (−) 6.5
Padparadscha Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Pink Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Ruby 0.018 1.762–1.770 Uniaxial (−) 9
Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Sinhalite 0.018 1.665–1.712 Biaxial (−) 6.5–7
Star Ruby 0.018 1.762–1.770 Uniaxial (−) 9
Star Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Synthetic Color-Change Corundum 0.018 1.762–1.770 Uniaxial (−) 9
White Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Yellow Sapphire 0.018 1.762–1.770 Uniaxial (−) 9
Calcite 0.017 1.486–1.658 Uniaxial (−) 3
Chrome Tourmaline 0.017 1.624–1.660 Uniaxial (−) 7–7.5
Danburite 0.017 1.627–1.636 Biaxial (−) 7–7.5
Enstatite 0.017 1.663–1.673 Biaxial (+) 5–5.5
Green Tourmaline 0.017 1.616–1.650 Uniaxial (−) 7–7.5
Hiddenite 0.017 1.660–1.676 Biaxial (+) 6.5–7
Indicolite 0.017 1.624–1.644 Uniaxial (−) 7–7.5
Iolite 0.017 1.540–1.560 Biaxial (−) 7–7.5
Kunzite 0.017 1.660–1.676 Biaxial (+) 6.5–7
Paraiba Tourmaline 0.017 1.624–1.644 Uniaxial (−) 7–7.5
Rubellite 0.017 1.624–1.644 Uniaxial (−) 7–7.5
Scapolite 0.017 1.540–1.572 Uniaxial (−) 6–6.5
Tourmaline 0.017 1.624–1.644 Uniaxial (−) 7–7.5
Watermelon Tourmaline 0.017 1.616–1.650 Uniaxial (−) 7–7.5
Andalusite 0.016 1.629–1.649 Biaxial (−) 7–7.5
Rhodonite 0.016 1.716–1.752 Biaxial (+) 5.5–6.5
Variscite 0.016 1.560–1.594 Biaxial (−) 3.5–4.5
Alexandrite 0.015 1.746–1.755 Biaxial (+) 8.5
Cat's Eye Chrysoberyl 0.015 1.746–1.755 Biaxial (+) 8.5
Chrysoberyl 0.015 1.746–1.755 Biaxial (+) 8.5
Grandidierite 0.015 1.590–1.623 Biaxial (−) 7–7.5
Phenakite 0.015 1.654–1.670 Uniaxial (+) 7.5–8
Rhodochrosite 0.015 1.600–1.820 Uniaxial (−) 3.5–4
Aquamarine 0.014 1.577–1.583 Uniaxial (−) 7.5–8
Emerald 0.014 1.565–1.602 Uniaxial (−) 7.5–8
Goshenite 0.014 1.577–1.583 Uniaxial (−) 7.5–8
Heliodor 0.014 1.568–1.580 Uniaxial (−) 7.5–8
Morganite 0.014 1.572–1.600 Uniaxial (−) 7.5–8
Red Beryl 0.014 1.564–1.574 Uniaxial (−) 7.5–8
Topaz 0.014 1.609–1.643 Biaxial (+) 8
Agate 0.013 1.530–1.543 Aggregate 6.5–7
Amethyst 0.013 1.544–1.553 Uniaxial (+) 7
Ametrine 0.013 1.544–1.553 Uniaxial (+) 7
Apatite 0.013 1.628–1.649 Uniaxial (−) 5
Aventurine 0.013 1.544–1.553 Aggregate 7
Bloodstone 0.013 1.530–1.543 Aggregate 6.5–7
Carnelian 0.013 1.530–1.543 Aggregate 6.5–7
Chalcedony 0.013 1.530–1.543 Aggregate 6.5–7
Chrysocolla Chalcedony 0.013 1.530–1.543 Aggregate 6.5–7
Chrysoprase 0.013 1.530–1.543 Aggregate 6.5–7
Citrine 0.013 1.544–1.553 Uniaxial (+) 7
Hawk's Eye 0.013 1.544–1.553 Aggregate 7
Onyx 0.013 1.530–1.543 Aggregate 6.5–7
Prasiolite 0.013 1.544–1.553 Uniaxial (+) 7
Rock Crystal 0.013 1.544–1.553 Uniaxial (+) 7
Rose Quartz 0.013 1.544–1.553 Uniaxial (+) 7
Smoky Quartz 0.013 1.544–1.553 Uniaxial (+) 7
Star Diopside 0.013 1.664–1.721 Biaxial (+) 5–6
Tiger's Eye 0.013 1.544–1.553 Aggregate 7
Amazonite 0.012 1.514–1.530 Biaxial (−) 6–6.5
Labradorite 0.012 1.559–1.573 Biaxial (+) 6–6.5
Moonstone 0.012 1.518–1.526 Biaxial (−) 6–6.5
Rainbow Moonstone 0.012 1.559–1.572 Biaxial (−) 6–6.5
Sunstone 0.012 1.537–1.572 Biaxial (−) 6–6.5
Thulite 0.012 1.691–1.704 Biaxial (+) 6–7
Larimar 0.010 1.595–1.640 Biaxial (+) 4.5–5
Moldavite 0.010 1.480–1.510 SR 5.5
Obsidian 0.010 1.480–1.510 SR 5–5.5
Sugilite 0.010 1.607–1.610 Uniaxial (−) 5.5–6.5
Fluorite 0.007 1.432–1.436 SR 4
Charoite 0.005 1.550–1.559 Aggregate 5–6
Amber — 1.539–1.545 SR 2–2.5
Black Opal — 1.440–1.460 SR 5.5–6.5
Chrysocolla — 1.575–1.635 Aggregate 2–4
Coral — 1.486–1.658 Aggregate 3–4
Fire Opal — 1.370–1.470 SR 5.5–6.5
Hematite — 2.940–3.220 Uniaxial (−) 5.5–6.5
Howlite — 1.583–1.608 Aggregate 3.5
Ivory — 1.535–1.540 Aggregate 2.5–3
Jadeite — 1.654–1.688 Aggregate 6.5–7
Jet — 1.640–1.680 SR 2.5–4
Lapis Lazuli — 1.500–1.670 Aggregate 5–6
Nephrite — 1.600–1.627 Aggregate 6–6.5
Pearl — 1.520–1.690 Aggregate 2.5–4.5
Pietersite — 1.534–1.540 Aggregate 6.5–7
Serpentine — 1.560–1.571 Aggregate 3–6
Sodalite — 1.483–1.487 Aggregate 5.5–6
Turquoise — 1.610–1.650 Aggregate 5–6

Click a column header to re-sort the table.

Which gemstone has the highest dispersion?
Among the 132 gems in this reference, Cinnabar has the highest dispersion at 0.400, followed by Sphalerite (0.156), Cuprite (0.155), Moissanite (0.104). For comparison, diamond measures 0.044.

Does moissanite have more fire than diamond?
Yes — moissanite's dispersion is 0.104 against diamond's 0.044, well over double. Excessive rainbow fire in a supposed diamond is a practical first flag for moissanite, confirmed by its doubled facets (birefringence 0.043).

Why do some species show — instead of a dispersion value?
No dispersion value is recorded for 17 species in this chart. 15 of them are aggregates or never transparent, so fire is not an observable property; the other 2 (amber, fire opal) simply have no value recorded here. A dash means "not recorded", not a dispersion of zero.

All instrument charts: Refractive Index  ·  Specific Gravity  ·  Mohs Hardness  ·  Birefringence  ·  Fluorescence  ·  Pleochroism  ·  Spectroscope  ·  Optic Character  ·  Chelsea & Hanneman Filters  ·  Magnetism

See also: Full Reference Database  ·  How to Identify a Gemstone  ·  Exam Study Guides  ·  Open dataset (CSV & JSON, CC BY 4.0)

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