Gemstone Refractive Index: The Definitive Guide

This illustrated chart shows refractive index values for 155 natural gemstone varieties. It is the most complete and accurate refractive index scale for gemstones available online, and includes many rare varieties. 

Click on a gem link to see examples or find more information.

  Gem Variety Refractive
Index
Double
Refraction
Hematite Hematite 2.940-3.220 0.287
Cinnabar Cinnabar 2.905-3.256 0.351
Cuprite Cuprite 2.849 none
Natural Diamond Diamond 2.417-2.419 none
Sphalerite Sphalerite 2.368-2.371 none 
Cassiterite Cassiterite 1.997-2.098  0.096-0.098
Scheelite Scheelite 1.918-1.937  0.010-0.018
Demantoid Garnet Demantoid
Garnet
1.88-1.94  none
Uvarovite Garnet Uvarovite
Garnet
1.865 none
Sphene (Titanite) Sphene 
(Titanite)
1.843-2.110 0.100-0.192
Zircon Zircon 1.810-2.024 0.002-0.059
Cerussite Cerussite 1.804-2.079 0.274
Spessartite Garnet Spessartite
Garnet
1.790-1.820 none
Painite Painite 1.787-1.816 0.029
Almandine Garnet Almandine 
Garnet
1.770-1.820 none
Natural Ruby Ruby 1.762-1.778 0.008 
Star Ruby Star Ruby 1.762-1.778 0.008 
Sapphire Sapphire 1.762-1.778 0.008
Star Sapphire Star
Sapphire
1.762-1.778 0.008 
Mali Garnet Mali Garnet 1.760-1.780 none
Benitoite Benitoite 1.757-1.804 0.047
Color Change Alexandrite Alexandrite 1.746-1.763 0.007-0.011
Alexandite Cat's Eye Alexandrite
Cat's Eye
1.746-1.763 0.007-0.011
Chrysoberyl Chrysoberyl 1.746-1.763 0.007-0.011 
Chrysoberyl Cat's Eye Chrysoberyl
Cat's Eye
1.746-1.763 0.007-0.011 
Vanadium Chrysoberyl Vanadium
Chrysoberyl
1.746-1.763 0.007-0.011 
Rhodolite Garnet Rhodolite
Garnet
1.742-1.785 none
Color Change Garnet Color-Change 
Garnet
1.742-1.780 none
Malaia Garnet Malaia Garnet 1.742-1.780 none
Grossular Garnet Grossular
Garnet
1.734-1.759 none
Tsavorite Garnet Tsavorite
Garnet
1.734-1.759 none
Leuco Garnet Leuco Garnet 1.734-1.759 none
Hessonite Garnet Hessonite
Garnet
1.730-1.757 none
Epidote Epidote 1.729-1.768 0.015-0.049
Bastnasite Bastnasite 1.720-1.820 0.100
Azurite Azurite 1.720-1.848 0.108-0.110
Pyrope Garnet Pyrope
Garnet
1.720-1.756  none
Taaffeite Taaffeite 1.719-1.730 0.004-0.009
Rhodonite Rhodonite 1.716-1.752 0.010-0.014
Spinel Spinel 1.712-1.782  none
Kyanite Kyanite 1.710-1.734 0.015-0.033
Diaspore Diaspore 1.702-1.750 0.048
Serendibite Serendibite 1.701-1.743 0.005
Idocrase (Vesuvianite) Idocrase 
(Vesuvianite)
1.700-1.723  0.002-0.012
Tanzanite Tanzanite 1.691-1.700 0.009
Zoisite Zoisite 1.691-1.700 0.009
Dumortierite Dumortierite 1.678-1.689 0.015-0.037
Sinhalite Sinhalite 1.665-1.712 0.036-0.042
Chrome Diopside Chrome
Diopside
1.664-1.730 0.024-0.031
Diopside Diopside 1.664-1.730 0.024-0.031
Kornerupine Kornerupine 1.660-1.699 0.012-0.017
Hiddenite Hiddenite 1.660-1.681 0.014-0.016
Kunzite Kunzite 1.660-1.681 0.014-0.016
Spodumene Spodumene 1.660-1.681 0.014-0.016
Axinite Axinite 1.656-1.704 0.010-0.012
Malachite Malachite 1.666-1.909 0.254
Sillimanite Sillimanite 1.655-1.684 0.014-0.021
Jadeite Jade Jadeite Jade 1.652-1.688 0.020
Peridot Peridot 1.650-1.703 0.036-0.038
Enstatite Enstatite 1.650-1.680 0.009-0.012
Euclase Euclase 1.650-1.677 0.019-0.025
Phenakite Phenakite 1.650-1.670 0.016
Dioptase Dioptase 1.644-1.709 0.051-0.053
Jet Jet 1.640-1.680 none
Jeremejevite Jeremejevite 1.637-1.653 0.007-0.013
Barite Barite 1.636-1.648 0.012
Danburite Danburite 1.630-1.636 0.006-0.008
Clinohumite Clinohumite 1.629-1.674 0.028-0.041
Apatite Apatite 1.628-1.649 0.002-0.006
Cat's Eye Apatite Cat's Eye
Apatite
1.628-1.649 0.002-0.006
Andalusite Andalusite 1.627-1.649 0.007-0.013
Smithsonite Smithsonite 1.621-1.849 0.228
Datolite Datolite 1.621-1.675 0.040-0.060
Celestine Celestine 1.619-1.635 0.010-0.012
Chrome Tourmaline Chrome 
Tourmaline
1.614-1.666 0.014-0.032
Paraiba Tourmaline Paraiba 
Tourmaline
1.614-1.666 0.014-0.032
Rubellite Tourmaline Rubellite 
Tourmaline
1.614-1.666 0.014-0.032
Tourmaline Tourmaline 1.614-1.666 0.014-0.032
Actinolite Actinolite 1.614-1.653 0.020-0.025
Hemimorphite Hemimorphite 1.614-1.638 0.022
Prehnite Prehnite 1.611-1.669 0.021-0.039
Gaspeite Gaspeite 1.610-1.810 0.22
Turquoise Turquoise 1.610-1.650 0.040
Topaz Topaz 1.609-1.643  0.009-0.016
Imperial Topaz Imperial
Topaz
1.609-1.643  0.009-0.016 
Sugilite Sugilite 1.607-1.611 0.001-0.004
Brazilianite Brazilianite 1.602-1.623 0.019-0.021
Pezzotaite Pezzotaite 1.601-1.620 0.008-0.011
Rhodochrosite Rhodochrosite 1.600-1.820 0.208-0.220
Nephrite Jade Nephrite Jade 1.600-1.627 0.027
Larimar Larimar 1.595-1.645 0.038
Eudialyte Eudialyte 1.591-1.633 0.003-0.010
Grandidierite Grandidierite 1,590-1.623 0.033
Howlite Howlite 1.586-1.605 0.019
Amblygonite Amblygonite 1.578-1.646 0.024-0.030
Emerald Emerald 1.565-1.602 0.005
Aquamarine Aquamarine 1.565-1.602 0.005
Morganite Morganite 1.562-1.605  0.004-0.010
Goshenite Beryl Goshenite
Beryl
1.562-1.605 0.004-0.010 
Golden Beryl Golden Beryl 1.562-1.605 0.004-0.010  
Red Beryl Red Beryl
(Bixbite)
1.562-1.605 0.004-0.010 
Labradorite Labradorite 1.559-1.570 0.008-0.010
Hambergite Hambergite 1.553-1.628  0.072
Charoite Charoite 1.550-1.561 0.004-0.009
Amethyst Amethyst 1.544-1.553 0.009 
Aventurine Aventurine 1.544-1.553  0.009
Ametrine Ametrine 1.544-1.553 0.009 
Citrine Citrine 1.544-1.553 0.009 
Gem Silica Gem Silica 1.544-1.553 0.009 
Rock Crystal Rock Crystal 1.544-1.553 0.009 
Rose Quartz Rose
Quartz
1.544-1.553 0.009 
Smoky Quartz Smoky
Quartz
1.544-1.553 0.009 
Andesine Andesine 1.543-1.551 0.009
Iolite Iolite 1.542-1.578 0.008-0.012
Scapolite Scapolite 1.540-1.579 0.009-0.037
Jasper Jasper 1.54 none
Amber Amber 1.539-1.545 none
Oligoclase Oligoclase 1.538-1.550 0.007-0.013
Aragonite Aragonite 1.530-1.685 0.155
Williamsite Williamsite 1.530-1.575 0.001-0.002
Agate Agate 1.530-1.540 0.004-0.009
Bloodstone Bloodstone 1.530-1.540 0.004-0.009
Chalcedony Chalcedony 1.530-1.540 0.004-0.009
Chrome Chalcedony Chrome 
Chalcedony
1.530-1.540 0.004-0.009
Carnelian Carnelian 1.530-1.540 0.004-0.009
Chrysoprase Chrysopase 1.530-1.540 0.004-0.009
Onyx Onyx 1.530-1.540 0.004-0.009
Lepidolite Lepidolite 1.525-1.587 0.013
Sunstone Sunstone 1.525-1.548 0.010
Amazonite Amazonite 1.522-1.530 0.008
Pearl Pearl 1.52-1.69 0.158
Ammolite Ammolite
(Korite)
1.52-1.68 0.155
Orthoclase Orthoclase 1.518-1.530 0.008
Moonstone Moonstone 1.518-1.528 0.008
Carletonite Carletonite 1.517-1.521 0.004
Poudretteite Poudretteite 1.511-1.532 0.021
Petalite Petalite 1.502-1.518 0.012-0.017
Lapis Lazuli Lapis Lazuli 1.50 none
Hauyne Hauyne 1.498-1.510 none
Ulexite Ulexite 1.491-1.520 0.029
Calcite Calcite 1.486-1.658 0.172
Cobaltoalcite Cobaltoalcite 1.486-1.658 0.172
Coral Coral 1.486-1.658 0.160-0.172
Moldavite Moldavite 1.48-1.54 none
Hackmanite Hackmanite 1.48 none
Sodalite Sodalite 1.48 none
Chrysocolla Chrysocolla 1.46-1.57 0.023-0.040
Obsidian Obsidian 1.45-1.55 none
Fluorite Fluorite 1.434 none
Mexican Fire Opal Mexican 
Fire Opal
1.37-1.52 none
Opal Opal 1.37-1.52 none

In gemology, refractive index is one of the chief means of identifying a gemstone. It is measured using an instrument known as a refractometer.

The refractive index (often abbreviated RI) is an optical property that refers to the ratio of the speed of light in a vacuum to the speed of light through a transparent medium. Light is bent as it moves from air to another material, an effect familiar from observing how a stick partially immersed in water appears to be bent.

Gems with a higher refractive index tend to show more brilliance, since light is bent at a higher angle when it passes into the material. More light is then reflected back out the crown to the eye, rather than passing straight through the gem.

Most gemstones have 2 refractive indices, since light is split into 2 beams travelling at different speeds when it enters the gem. This phenomenon is known as birefringence or double refraction, and it is expressed as a value that indicates the difference between the two RI's for the gem material.

Some gemstones are singly refractive and have only 1 RI. Singly refractive gems include diamond, spinel and all the garnets, as well as other cubic crystals like cuprite, fluorite and sphalerite. Amorphous gems -- those with no crystal structure -- are also singly refractive.

See also:

Gemstone Hardness Chart

Gemstone Density Chart

 

 

 

 
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