For gemologists, refractive index and double refraction (birefringence) serve as important clues for identifying gems. The following table lists these values for a variety of stones found in jewelry and gem collections. [Reading time: 3 min]
spinel - gemstone refractive indices and double refraction

Rubies and spinels may show similar colors. One of the simplest ways to distinguish these gems is to test for double refraction with a dichroscope. Since spinels have an isometric crystal structure, they have no double refraction. On the other hand, rubies do have double refraction. Brilliant-cut oval spinel, 6.88 cts, recut by AGTA Spectrum Award-winner Mark Kaufman. Mogok gem tract, Myanmar. © Rob Lavinsky, www.iRocks.com. Used with permission.

Refractive Indices and Double Refraction Values

The following table organizes gemstones from highest to lowest refractive indices.

Gemstone Refractive Index Double Refraction
Hematite 2.940-3.220 0.287
Cinnabar 2.905-3.256 0.351
Proustite 2.881-3.084 0.203
Pyrargyrite 2.880-3.080 0.200
Cuprite 2.849 none
Rutile 2.616-2.903 0.287
Brookite 2.583-2.700 0.117
Anatase 2.488-2.564 0.046-0.067
Diamond 2.417-2.419 anomalous
Fabulite 2.409 none
Stibiotantalite 2.370-2.450 0.080
Sphalerite 2.368-2.371 none
Crocoite 2.290-2.660 0.270
Wulfenite 2.280-2.400 0.120
Tantalite 2.260-2.430 0.160
Linobate 2.210-2.300 0.090
Manganotantalite 2.190-2.340 0.150
Cubic zirconia (CZ) 2.150-2.180 none
Mimetite 2.120-2.135 0.015
Phosgenite 2.114-2.145 0.028
Senarmontite 2.087 none
Boleite 2.030-2.050 0.020
Zincite 2.013-2.029 0.016
Cassiterite 1.997-2.098 0.096-0.098
Simpsonite 1.994-2.040 0.058
Gadolinium gallium garnet (GGG) 1.970-2.020 0.058
Sulfur 1.958-2.245 0.291
Bayldonite 1.950-1.990 0.04
Scheelite 1.918-1.937 0.010-0.018
Andradite garnet 1.880-1.940 none
Anglesite 1.878-1.895 0.017
Uvarovite garnet 1.865 none
Purpurite 1.850-1.920 0.007
Sphene (titanite) 1.843-2.110 0.100-0.192
Yttrium aluminum garnet (YAG) 1.833-1.835 none
Zircon 1.810-2.024 0.002-0.059
Cerussite 1.804-2.079 0.274
Gahnite 1.791-1.818 none
Spessartite garnet 1.790-1.820 none
Painite 1.787-1.816 0.029
Monazite 1.774-1.849 0.049-0.055
Almandine garnet 1.770-1.820 none
Gadolinite 1.770-1.820 0.01-0.04
Ruby (corundum) 1.762-1.778 0.008
Sapphire (corundum) 1.762-1.778 0.008
Benitoite 1.757-1.804 0.047
Shattuckite 1.752-1.815 0.063
Chrysoberyl 1.746-1.763 0.007-0.011
Periclase 1.740 none
Scorodite 1.738-1.816 0.027-0.030
Staurolite 1.736-1.762 0.010-0.015
Grossular garnet 1.734-1.759 none
Chambersite 1.732-1.744 0.012
Hessonite garnet 1.730-1.757 none
Epidote 1.729-1.768 0.015-0.049
Pyroxmangite 1.726-1.764 0.016-0.020
Azurite 1.720-1.848 0.108-0.110
Pyrope garnet 1.720-1.756 none
Hodgkinsonite 1.719-1.748 0.022-0.026
Taaffeite 1.719-1.730 0.004-0.009
Rhodonite 1.716-1.752 0.010-0.014
Gahnospinel 1.715-1.754 none
Spinel 1.712-1.762 none
Kyanite 1.710-1.734 0.015-0.033
Adamite 1.708-1.760 0.048-0.050
Diaspore 1.702-1.750 0.048
Serendibite 1.701-1.743 0.005
Sapphirine 1.701-1.734 0.004-0.007
Aegirine-augite 1.700-1.800 0.030-0.050
Idocrase (vesuvianite) 1.700-1.723 0.002-0.012
Tanzanite 1.691-1.700 0.009
Neptunite 1.690-1.736 0.029-0.045
Willemite 1.690-1.723 0.028-0.033
Rhodizite 1.690 none
Triphylite 1.689-1.702 0.006-0.008
Lithiophilite 1.680-1.700 0.01
Dumortierite 1.678-1.689 0.015-0.037
Legrandite 1.675-1.740 0.060
Hypersthene 1.673-1.731 0.010-0.016
Parisite 1.671-1.772 0.081-0.101
Clinozoisite 1.670-1.734 0.010
Sinhalite 1.665-1.712 0.036-0.042
Lawsonite 1.665-1.686 0.019-0.021
Diopside 1.664-1.730 0.024-0.031
Bustamite 1.662-1.707 0.014-0.015
Kornerupine 1.660-1.699 0.012-0.017
Hiddenite 1.660-1.681 0.014-0.016
Kunzite 1.660-1.681 0.014-0.016
Boracite 1.658-1.673 0.010-0.011
Axinite 1.656-1.704 0.010-0.012
Malachite 1.655-1.909 0.254
Sillimanite 1.655-1.684 0.014-0.021
Jadeite 1.652-1.688 0.20
Peridot 1.650-1.703 0.036-0.038
Ludlamite 1.650-1.697 0.038-0.044
Enstatite 1.650-1.680 0.009-0.012
Euclase 1.650-1.677 0.019-0.025
Phenakite 1.650-1.670 0.016
Dioptase 1.644-1.709 0.051-0.053
Jet 1.640-1.680 none
Eosphorite 1.638-1.671 0.028-0.035
Spurrite 1.637-1.681 0.039-0.040
Jeremejevite 1.637-1.653 0.007-0.013
Barite 1.636-1.648 0.012
Siderite 1.633-1.875 0.242
Danburite 1.630-1.636 0.006-0.008
Clinohumite 1.629-1.674 0.028-0.041
Apatite 1.628-1.649 0.002-0.006
Andalusite 1.627-1.649 0.007-0.013
Friedelite 1.625-1.664 0.030
Smithsonite 1.621-1.849 0.228
Datolite 1.621-1.675 0.040-0.050
Celestite 1.619-1.635 0.010-0.012
Tourmaline 1.614-1.666 0.014-0.032
Actinolite 1.614-1.653 0.020-0.025
Hemimorphite 1.614-1.636 0.022
Lazulite 1.612-1.646 0.031-0.036
Prehnite 1.611-1.669 0.021-0.039
Gaspéite 1.610-1.810 0.22
Turquoise 1.610-1.650 0.040
Topaz 1.609-1.643 0.008-0.016
Sugilite 1.607-1.611 0.001-0.004
Sogdianite 1.606-1.608 0.002
Brazilianite 1.602-1.623 0.019-0.021
Rhodochrosite 1.600-1.820 0.208-0.220
Odontolite 1.600-1.640 0.010
Nephrite 1.600-1.627 0.027
Pectolite (larimar) 1.595-1.645 0.038
Montebrasite 1.594-1.633 0.22
Phosphophyllite 1.594-1.621 0.021-0.033
Meliphanite 1.593-1.612 0.019
Eudialyte 1.591-1.633 0.003-0.010
Chondrodite 1.592-1.646 0.028-0.034
Catapleiite 1.590-1.629 0.039
Wardite 1.590-1.599 0.009
Herderite 1.587-1.627 0.023-0.032
Colemanite 1.586-1.615 0.028-0.030
Howlite 1.586-1.605 0.019
Zektzerite 1.582-1.585 0.003
Amblygonite 1.578-1.646 0.024-0.030
Ekanite 1.572-1.573 0.001
Anhydrite 1.570-1.614 0.044
Augelite 1.570-1.590 0.014-0.020
Emerald (beryl) 1.565-1.602 0.006
Aquamarine (beryl) 1.564-1.596 0.004-0.005
Variscite 1.563-1.594 0.031
Beryl (precious) 1.562-1.602 0.004-0.010
Tremolite 1.560-1.643 0.017-0.027
Vivianite 1.560-1.640 0.050-0.075
Serpentine 1.560-1.571 0.008-0.014
Larbradorite 1.559-1.570 0.008-0.010
Hambergite 1.553-1.628 0.072
Pyrophyllite 1.552-1.600 0.048
Muscovite 1.552-1.618 0.036-0.043
Beryllonite 1.552-1.561 0.009
Charoite 1.550-1.561 0.004-0.009
Amethyst (quartz) 1.544-1.553 0.009
Aventurine (quartz) 1.544-1.553 0.009
Rose quartz 1.544-1.553 0.009
Citrine (quartz) 1.544-1.553 0.009
Prasiolite (quartz) 1.544-1.553 0.009
Smoky quartz 1.544-1.553 0.009
Rock crystal (quartz) 1.544-1.553 0.009
Andesine 1.543-1.551 0.008
Cordierite 1.542-1.578 0.008-0.012
Oligoclase 1.542-1.549 0.007
Talc 1.540-1.590 0.050
Scapolite 1.540-1.579 0.006-0.037
Petrified Wood 1.540 none
Jasper 1.540 none
Amber 1.539-1.545 none
Ivory 1.535-1.570 none
Apophyllite 1.535-1.537 0.002
Tiger’s eye 1.534-1.540 none
Aragonite 1.530-1.685 0.155
Agate 1.530-1.540 0.004-0.009
Chalcedony 1.530-1.540 0.004-0.009
Chrysoprase 1.530-1.540 0.004-0.009
Moss agate 1.530-1.540 0.004-0.009
Sepiolite 1.530 none
Witherite 1.529-1.677 0.148
Milarite 1.529-1.551 0.003
Nepheline 1.526-1.546 0.0004
Sunstone 1.525-1.548 0.01
Amazonite 1.522-1.530 0.008
Pearl 1.520-1.690 0.156
Ammolite 1.520-1.680 0.155
Strontianite 1.520-1.670 0.150
Gypsum 1.520-1.529 0.009
Orthoclase 1.518-1.530 0.008
Sanidine 1.518-1.530 0.008
Moonstone 1.518-1.526 0.008
Pollucite 1.517-1.525 none
Carletonite 1.517-1.521 0.004
Stichtite 1.516-1.544 0.026
Thomsonite 1.515-1.542 0.006-0.025
Magnesite 1.509-1.717 0.022
Scolecite 1.509-1.525 0.007-0.012
Leucite 1.504-1.509 0.001
Mesolite 1.504-1.508 0.001
Dolomite 1.502-1.698 0.185
Petalite 1.502-1.519 0.012-0.017
Lapis lazuli 1.500 none
Haüyne 1.496-1.510 none
Tugtupite 1.496-1.502 0.006
Cancrinite 1.495-1.528 0.024-0.029
Celluloid 1.495-1.520 none
Ulexite 1.491-1.520 0.029
Yugawaralite 1.490-1.509 0.011-0.014
Whewellite 1.489-1.651 0.159-0.163
Kurnakovite 1.488-1.525 0.036
Inderite 1.486-1.507 0.017-0.020
Calcite 1.486-1.658 0.172
Coral 1.486-1.658 0.160-0.172
Moldavite 1.48-1.540 none
Natrolite 1.480-1.493 0.013
Sodalite 1.480 none
Analcime 1.479-1.489 none
Thaumasite 1.464-1.507 0.036
Creedite 1.461-1.485 0.024
Chrysocolla 1.460-1.570 0.023-0.040
Obsidian 1.450-1.550 none
Gaylussite 1.443-1.523 0.080
Glass 1.440-1.900 none
Fluorite 1.434 none
Sellaite 1.378-1.390 0.012
Opal 1.370-1.520 none

Notes

A double refraction of “none” means the stone is either isometric or amorphous. “Anomalous” means this singly refractive stone may show anomalous double refraction (ADR). Singly refractive gems with high refractive indices may show ADR.