Dispersion of Gemstones — Fire Reference Chart

Last updated: August 2026

Dispersion values (the B–G interval) for 130 gemstone species, 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 recorded at 0.000 (opaque and aggregate materials) display no fire at all.

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

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Gem Dispersion (B–G) RI Range Optic Character Hardness
Cinnabar 0.400 2.905–3.256 Uniaxial (+) 2–2.5
Sphalerite 0.156 2.369–2.500 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 2.010–2.100 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 6–7.5
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 1.685–1.752 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
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 1.560–1.590 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
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 0.000 1.539–1.545 SR 2–2.5
Black Opal 0.000 1.440–1.460 SR 5.5–6.5
Chrysocolla 0.000 1.460–1.630 Aggregate 2.5–7
Coral 0.000 1.486–1.658 Aggregate 3–4
Fire Opal 0.000 1.370–1.470 SR 5.5–6.5
Hematite 0.000 2.940–3.220 Uniaxial (−) 5.5–6.5
Howlite 0.000 1.583–1.608 Aggregate 3.5
Ivory 0.000 1.535–1.540 Aggregate 2.5–3
Jadeite 0.000 1.654–1.688 Aggregate 6.5–7
Jet 0.000 1.640–1.680 SR 2.5–4
Lapis Lazuli 0.000 1.500–1.670 Aggregate 5–6
Nephrite 0.000 1.600–1.627 Aggregate 6–6.5
Pearl 0.000 1.520–1.690 Aggregate 2.5–4.5
Pietersite 0.000 1.534–1.540 Aggregate 6.5–7
Serpentine 0.000 1.560–1.571 Aggregate 3–4
Sodalite 0.000 1.483–1.487 Aggregate 5.5–6
Turquoise 0.000 1.610–1.650 Aggregate 5–6

Click a column header to re-sort the table.

Which gemstone has the highest dispersion?
Among the 130 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).

What does a dispersion value of 0.000 mean?
It is recorded for materials that display no fire — opaque, translucent-aggregate, and organic materials where spectral separation is not observable. 17 species in this chart carry a 0.000 value.

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