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Refractive Index
of Gems   (Index of Refraction)

    

Click HERE for the  Alphabetical  Refractive  Index  List.
Click
HERE for the  Numerical  Refractive  Index  List.

 

 

Refractive Index (RI) is the characteristic slowing of light as it travels through a given gem species or substance. The higher the RI, the greater brilliance and luster is possible. The fact that each gem has its own RI makes it necessary to facet each species at slightly different angles and makes it a useful characteristic in gem identification.

What is the Index of Refraction?
Light moves at its maximum possible velocity in the absence of matter. For example, in space light travels approximately 186,000 miles per second. But the presence of matter slows light down; or more specifically, the forces which bind atoms slow light down. The Index of Refraction for any substance is the ratio of the velocity of light in a vacuum to its velocity in a given substance. The higher the index, the slower the velocity. Thus, if we say that a particular crystal has an index of refraction of 2.000 we mean that light would pass through a vacuum at twice the velocity that it can go through that crystal.

Why do different substances have different refractive indices?
As previously pointed out, the velocity of light through any material is retarded by forces binding its atoms and molecules. Therefore, the degree to which a particular beam of light is slowed depends both upon the types of atoms present (the chemical composition) and the nature of the arrangement of those atoms.

For example, light travels in water at 3/4 of its velocity in a vacuum, so we assign a value of 4/3, or 1.333 as the index of refraction of water. But if we freeze that water into ice, a different arrangement of the molecules results and the ice has a refractive index of 1.313. Or, if we boil the water, yet another arrangement of the same molecules is produced, which retards the light very little, and the steam has a refractive index of 1.0002.

In the case of ice, water and steam, we have examples of three different states of matter; solid, liquid and gas. But, even when a single state of matter is considered, it must be remembered that the identical materials can often be arranged in different structures, which are reflected in the differing indices of refraction.

For example, common pure Quartz crystals have an average index of 1.548. But if the crystal is melted and then cooled down to room temperature, the resulting fused silica-quartz has an index of 1.456. Or the same silicon dioxide may also exist as tridymite, cristobalite, coesite or other differing crystal structures, each of which has a different refractive index, although all have the identical chemical composition.

Does light always travel through a given crystal at the same speed?
No. Most minerals crystallize in an orderly lattice work that has different types of inter-molecular bonds in different planes, much like the grain in wood. The strength of these bonds may be very different in different planes.

The form of Calcite known as Iceland Spar presents an outstanding example of the effect on refractive index in different optical directions, since a given crystal will have an index of 1.486 in one direction and 1.658 in another. Fortunately (except for Rutile) most minerals used as gems do not vary so widely in different directions.

What other factors affect the Refractive Index of a mineral?
Temperature of the specimen influences its index, but if measurements are made at a normal range of room temperatures, this effect is so small that it can be neglected.

Impurities in the specimen have an effect proportionate to their concentration in the specimen. For example, Opal consists mainly of a form of silica known as cristobalite with an index of 1.487. But Opal usually contains about 5 to 10% of water in its structure. Since water has an index of 1.33, Opals show an index somewhere between those two values, usually 1.43 to 1.46.

  

Refractive Index of Gems   (Index of Refraction)

Alphabetical  RI  List

Click HERE for the Numerical  RI  List.

Actinolite
Adventurine (Quartz)
Aegirine
Agate
Air (as a reference)
Albite (Feldspar)
Alexandrite
Allanite
Almandine (Garnet)
Amazonite (Feldspar)
Amber
Amblygonite
Amethyst
Ametrine
Anatase
Andalusite
Andesine (Feldspar)
Andradite (Garnet)
Angelsite
Anhydrite
Anorthite (Feldspar)
Apatite
Apophyllite
Aquamarine (Beryl)
Aragonite
Augelite
Axinite
Azurite
Bahianite
Barite
Bastnäsite
Benitoite
Beryl Family
Beryllonite
Bixbite (Beryl)
Boracite
Brazilianite
Bronzite
Burbankite
Bytownite (Feldspar)
Calcite
Cancrinite
Carnelian
Cassiterite
Celestite
Cerussite
Chalcedony
Childrenite
Chkalovite
Chondrodite
Chrome Diopside
Chrysoberyl
Chrysocolla
Chrysoprase
Citrine
Clinozoisite
Colemanite
Coral
Crocoite
Cubic Zirconia
Cuprite
Danburite
Datolite
Demantoid (Garnet)
Diamond
Diopside
Dioptase
Dolomite
Dumortierite
Dunilite
Ekanite
Emerald (Beryl)
Emerald (synth. flux)
Emerald (synth. hydro)
Enstatite
Epidote
Euclase
Fayalite (Olivine)
Fluorite
Friedelite
Gahnite
Gahnospinel
Genthelvite
Glass (man-made)
Gold
Goshenite (Beryl)
Grossular (Garnet)
Hackmanite
Hambergite
Hauyne
Heliodor (Beryl)
Hematite
Hemimorphite
Herderite
Hessonite (Garnet)
Hiddenite (Spodumene)
Howlite
Hydrogrossular (Garnet)
Hypersthene
Idocrase
Iolite
Ivory
Jadeite (Jade)
Jasper (Quartz)
Kentbrooksite
Kornerupine
Kunzite (Spodumene)
Kyanite
Labradorite (Feldspar)
Lapis Lazuli (Lazurite)
Lazulite
Legrandite
Leucite
Ludlamite
Magnesite
Malachite
Maw-Sit-Sit
Microline (Feldspar)
Moissanite
Moldavite
Montebrasite
Moonstone (Feldspar)
Morganite (Beryl)
Natrolite
Nephrite (Jade)
Obsidian
Oligoclase (Feldspar)
Onyx
Opal
Orthoclase (Feldspar)
Painite
Pearl
Pectolite
Periclase
Peridot (Olivine)
Peristerite
Petalite
Pezzottaite
Phenakite
Phosgenite
Phosphophyllite
Poldervaartite
Poudretteite
Powellite
Prasiolite (Quartz)
Prehnite
Proustite
Purpurite
Pyrope (Garnet)
Pyroxmangite
Quartz (all colors)
Rhodizite
Rhodochrosite
Rhodolite (Garnet)
Rhodonite
Richterite
Ruby (Corundum)
Rutile
Sanidine (Feldspar)
Sapphire (Corundum)
Sapphirine
Scapolite
Scheelite
Sellaite
Serendibite
Serpentine
Shattuckite
Shortite
Siderite
Sillimanite
Silver
Simpsonite
Sinhalite
Smithsonite
Sodalite
Spessartine (Garnet)
Sphalerite
Sphene
Spinel
Spinel (synthetic)
Spodumene
Staurolite
Steatite
Stibiotantalite
Strontium Titanate
Suolunite
Taaffeite
Tantalite
Tanzanite (Zoisite)
Tektite
Thaumasite
Thomsonite
Thulite (Zoisite)
Tiger eye (Quartz)
Topaz
Tourmaline (all colors)
Tremolite
Tsavorite (Garnet)
Tugtupite
Turquoise
Ulexite
Unakite
Uvarovite (Garnet)
Vanadinite
Variscite
Vesuvianite
Villiaumite
Vivianite
Water (at
20°C)
Willemite
Witherite
Wulfenite
Zektzerite
Zincite
Zircon, High
Zircon, Medium
Zircon, Low
Zoisite
   

1.614 - 1.655
1.544 - 1.553
1.720 - 1.839
1.535 - 1.539
1.0003
1.527 - 1.538
1.745 - 1.759
1.640 - 1.828
1.775 - 1.830
1.514 - 1.539
1.539 - 1.545
1.578 - 1.612
1.544 - 1.533
1.544 - 1.553
2.488 - 2.564
1.627 - 1.650
1.543 - 1.551
1.880 - 1.940
1.877 - 1.894
1.570 - 1.614
1.577 - 1.590
1.628 - 1.650
1.530 - 1.540
1.567 - 1.590
1.530 - 1.685
1.574 - 1.588
1.672 - 1.694
1.720 - 1.850
1.810 - 1.920
1.636 - 1.648
1.717 - 1.818
1.757 - 1.804
1.563 - 1.620
1.552 - 1.562
1.568 - 1.572
1.658 - 1.673
1.602 - 1.625
1.665 - 1.703
1.615 - 1.627
1.561 - 1.570
1.486 - 1.740
1.495 - 1.528
1.535 - 1.539
1.995 - 2.095
1.619 - 1.635
1.803 - 2.078
1.535 - 1.539
1.649 - 1.691
1.544 - 1.549
1.592 - 1.675
1.668 - 1.702
1.740 - 1.777
1.575 - 1.635
1.535 - 1.539
1.544 - 1.553
1.670 - 1.734
1.586 - 1.614
1.550 - 1.580
2.290 - 2.660
2.170 (iso)
2.848 (iso)
1.627 - 1.639
1.621 - 1.675
1.880 - 1.888
2.417 (iso)
1.664 - 1.721
1.645 - 1.720
1.500 - 1.703
1.668 - 1.723
1.677 - 1.718
1.590 - 1.596
1.575 - 1.602
1.553 - 1.580
1.563 - 1.620
1.650 - 1.680
1.715 - 1.797
1.650 - 1.677
1.827 - 1.879
1.432 - 1.434
1.625 - 1.664
1.790 - 1.820 (iso)
1.735 - 1.790
1.742 - 1.745
1.520 - 1.550
0.470 (iso)
1.566 - 1.602
1.730 - 1.760
1.483 - 1.487
1.550 - 1.630
1.496 - 1.505
1.566 - 1.579
2.880 - 3.220
1.614 - 1.636
1.591 - 1.624
1.742 - 1.748
1.653 - 1.682
1.583 - 1.608
1.690 - 1.730
1.686 - 1.772
1.655 - 1.761
1.533 - 1.596
1.535 - 1.555
1.640 - 1.667
1.544 - 1.553
1.623 - 1.628
1.665 - 1.700
1.653 - 1.682
1.710 - 1.735
1.560 - 1.572
1.500 (iso)
1.604 - 1.662
1.675 - 1.740
1.504 - 1.510
1.650 - 1.697
1.509 - 1.717
1.655 - 1.909
1.520 - 1.680
1.514 - 1.539
2.648 - 2.691
1.460 - 1.540
1.594 - 1.616
1.518 - 1.526
1.572 - 1.600
1.473 - 1.496
1.600 - 1.640
1.450 - 1.520
1.542 - 1.549
1.535 - 1.539
1.370 - 1.470
1.518 - 1.539
1.787 - 1.816
1.530 - 1.685
1.595 - 1.645
1.736 (iso)
1.650 - 1.681
1.531 - 1.546
1.502 - 1.520
1.607 - 1.619
1.650 - 1.695
2.114 - 2.145
1.595 - 1.621
1.634 - 1.656
1.510 - 1.532
1.967 - 1.985
1.544 - 1.553
1.611 - 1.665
2.792 - 3.088
1.850 - 1.920
1.730 - 1.766
1.726 - 1748
1.544 - 1.553
1.694 (iso)
1.578 - 1.840
1.745 - 1.760
1.711 - 1.752
1.615 - 1.636
1.757 - 1.779
2.620 - 2.900
1.518 - 1.534
1.757 - 1.779
1.714 - 1.723
1.536 - 1.596
1.918 - 1.936
1.37 - 1.39
1.701 - 1.706
1.490 - 1.575
1.752 - 1.815
1.531 - 1.570
1.633 - 1.873
1.654 - 1.683
0.180 (iso)
1.976 - 2.045
1.665 - 1.712
1.620 - 1.850
1.483 - 1.487
1.790 - 1.810
2.400 (iso)
1.900 - 2.034
1.712 - 1.735
1.710 - 1.740
1.653 - 1.682
1.736 - 1.762
1.539 - 1.600
2.37 - 2.46
2.400 (iso)
1.610 - 1.623
1.717 - 1.730
2.260 - 2.430
1.692 - 1.705
1.460 - 1.540
1.464 - 1.507
1.497 - 1.544
1.692 - 1.705
1.544 - 1.553
1.609 - 1.643
1.614 - 1.666
1.560 - 1.643
1.735 - 1.744
1.494 - 1.504
1.610 - 1.650
1.496 - 1.519
1.525 - 1.760
1.740 - 1.870
2.350 - 2.416
1.560 - 1.594
1.655 - 1.761
1.327 (iso)
1.569 - 1.675
1.3328
1.690 - 1.723
1.529 - 1.677
2.280 - 2.405
1.582 - 1.584
2.013 - 2.029
1.970 - 2.025
1.840 - 1.970
1.780 - 1.850
1.685 - 1.725
 

Numerical RI List

Hematite
Cuprite
Proustite
Moissanite
Rutile
Anatase
Diamond
Sphalerite
Strontium Titanate
Stibiotantalite
Vanadinite
Crocoite
Wulfenite
Tantalite
Cubic Zirconia
Phosgenite
Zincite
Cassiterite
Simpsonite
Zircon, High
Powellite
Scheelite
Sphene
Andradite (Garnet)
Demantoid (Garnet)
Angelsite
Purpurite
Zircon, Medium
Fayalite (Olivine)
Bahianite
Cerussite
Gahnite
Spessartine (Garnet)
Painite
Zircon, Low
Almandine (Garnet)
Benitoite
Ruby (Corundum)
Sapphire (Corundum)
Shattuckite
Rhodolite (Garnet)
Alexandrite
Hessonite (Garnet)
Genthelvite
Uvarovite (Garnet)
Chrysoberyl
Staurolite
Periclase
Gahnospinel
Tsavorite (Garnet)
Pyrope (Garnet)
Grossular (Garnet)
Pyroxmangite
Azurite
Aegirine
Bastnäsite
Taaffeite
Epidote
Sapphirine
Rhodonite
Spinel (synthetic)
Spinel
Kyanite
Serendibite
Rhodizite
Tanzanite (Zoisite)
Thulite (Zoisite)
Hydrogrossular (Garnet)
Willemite
Hypersthene
Zoisite
Dunilite
Legrandite
Axinite
Clinozoisite
Dumortierite
Chrome Diopside
Sinhalite
Kornerupine
Diopside
Idocrase
Vesuvianite
Bronzite
Boracite
Malachite
Sillimanite
Spodumene
Hiddenite (Spodumene)
Kunzite (Spodumene)
Ludlamite
Phenakite
Peridot (Olivine)
Enstatite
Euclase
Childrenite
Dioptase
Allanite
Jadeite (Jade)
Barite
Poldervaartite
Siderite
Apatite
Andalusite
Danburite
Friedelite
Kentbrooksite
Datolite
Smithsonite
Celestite
Richterite
Burbankite
Tourmaline (all colors)
Actinolite
Hemimorphite
Prehnite
Turquoise
Suolunite
Topaz
Pezzottaite
Lazulite
Brazilianite
Nephrite (Jade)
Pectolite
Phosphophyllite

Montebrasite
Chondrodite
Herderite
Ekanite
Colemanite
Howlite
Zektzerite
Rhodochrosite
Amblygonite
Anorthite (Feldspar)
Chrysocolla
Emerald (Beryl)
Augelite
Morganite (Beryl)
Anhydrite
Vivianite
Beryl Family
Bixbite (Beryl)
Aquamarine (Beryl)
Goshenite (Beryl)
Heliodor (Beryl)
Emerald (synth. hydro)
Bytownite (Feldspar)
Tremolite
Variscite
Labradorite (Feldspar)
Emerald (synth. flux)
Beryllonite
Hambergite
Coral
Adventurine (Quartz)
Amethyst
Ametrine
Citrine
Jasper (Quartz)
Prasiolite (Quartz)
Quartz (all colors)
Tiger eye (Quartz)
Chkalovite
Andesine (Feldspar)
Oligoclase (Feldspar)
Steatite
Amber
Scapolite
Ivory
Agate
Carnelian
Chalcedony
Chrysoprase
Onyx
Iolite
Shortite
Peristerite
Aragonite
Pearl
Apophyllite
Witherite
Albite (Feldspar)
Unakite
Maw-Sit-Sit
Glass (man-made)
Orthoclase (Feldspar)
Sanidine (Feldspar)
Moonstone (Feldspar)
Amazonite (Feldspar)
Microline (Feldspar)
Poudretteite
Magnesite
Leucite
Petalite
Dolomite
Lapis Lazuli (Lazurite)
Thomsonite
Ulexite
Hauyne
Cancrinite
Tugtupite
Serpentine
Calcite
Sodalite
Hackmanite
Natrolite
Thaumasite
Moldavite
Tektite
Obsidian
Fluorite
Opal
Sellaite
Water (at
20°C)
Villiaumite
Air (as a reference)
Gold
Silver
 

2.880 - 3.220
2.848 (iso)
2.792 - 3.088
2.648 - 2.691
2.620 - 2.900
2.488 - 2.564
2.417 (iso)
2.400 (iso)
2.400 (iso)
2.37 - 2.46
2.350 - 2.416
2.290 - 2.660
2.280 - 2.405
2.260 - 2.430
2.170 (iso)
2.114 - 2.145
2.013 - 2.029
1.995 - 2.095
1.976 - 2.045
1.970 - 2.025
1.967 - 1.985
1.918 - 1.936
1.900 - 2.034
1.880 - 1.940
1.880 - 1.888
1.877 - 1.894
1.850 - 1.920
1.840 - 1.970
1.827 - 1.879
1.810 - 1.920
1.803 - 2.078
1.790 - 1.820 (iso)
1.790 - 1.810
1.787 - 1.816
1.780 - 1.850
1.775 - 1.830
1.757 - 1.804
1.757 - 1.779
1.757 - 1.779
1.752 - 1.815
1.745 - 1.760
1.745 - 1.759
1.742 - 1.748
1.742 - 1.745
1.740 - 1.870
1.740 - 1.777
1.736 - 1.762
1.736 (iso)
1.735 - 1.790
1.735 - 1.744
1.730 - 1.766
1.730 - 1.760
1.726 - 1748
1.720 - 1.850
1.720 - 1.839
1.717 - 1.818
1.717 - 1.730
1.715 - 1.797
1.714 - 1.723
1.711 - 1.752
1.710 - 1.740
1.710 - 1.735
1.710 - 1.735
1.701 - 1.706
1.694 (iso)
1.692 - 1.705
1.692 - 1.705
1.690 - 1.730
1.690 - 1.723
1.686 - 1.772
1.685 - 1.725
1.677 - 1.718
1.675 - 1.740
1.672 - 1.694
1.670 - 1.734
1.668 - 1.723
1.668 - 1.702
1.665 - 1.712
1.665 - 1.700
1.664 - 1.721
1.655 - 1.761
1.655 - 1.761
1.665 - 1.703
1.658 - 1.673
1.655 - 1.909
1.654 - 1.683
1.653 - 1.682
1.653 - 1.682
1.653 - 1.682
1.650 - 1.697
1.650 - 1.695
1.650 - 1.681
1.650 - 1.680
1.650 - 1.677
1.649 - 1.691
1.645 - 1.720
1.640 - 1.828
1.640 - 1.667
1.636 - 1.648
1.634 - 1.656
1.633 - 1.873
1.628 - 1.650
1.627 - 1.650
1.627 - 1.639
1.625 - 1.664
1.623 - 1.628
1.621 - 1.675
1.620 - 1.850
1.619 - 1.635
1.615 - 1.636
1.615 - 1.627
1.614 - 1.666
1.614 - 1.655
1.614 - 1.636
1.611 - 1.665
1.610 - 1.650
1.610 - 1.623
1.609 - 1.643
1.607 - 1.619
1.604 - 1.662
1.602 - 1.625
1.600 - 1.640
1.595 - 1.645
1.595 - 1.621
1.594 - 1.616
1.592 - 1.675
1.591 - 1.624
1.590 - 1.596
1.586 - 1.614
1.583 - 1.608
1.582 - 1.584
1.578 - 1.840
1.578 - 1.612
1.577 - 1.590
1.575 - 1.635
1.575 - 1.602
1.574 - 1.588
1.572 - 1.600
1.570 - 1.614
1.569 - 1.675
1.563 - 1.620
1.568 - 1.572
1.567 - 1.590
1.566 - 1.602
1.566 - 1.579
1.563 - 1.620
1.561 - 1.570
1.560 - 1.643
1.560 - 1.594
1.560 - 1.572
1.553 - 1.580
1.552 - 1.562
1.550 - 1.630
1.550 - 1.580
1.544 - 1.553
1.544 - 1.553
1.544 - 1.553
1.544 - 1.553
1.544 - 1.553
1.544 - 1.553
1.544 - 1.553
1.544 - 1.553
1.544 - 1.549
1.543 - 1.551
1.542 - 1.549
1.539 - 1.600
1.539 - 1.545
1.536 - 1.596
1.535 - 1.555
1.535 - 1.539
1.535 - 1.539
1.535 - 1.539
1.535 - 1.539
1.535 - 1.539
1.533 - 1.596
1.531 - 1.570
1.531 - 1.546
1.530 - 1.685
1.530 - 1.685
1.530 - 1.543
1.529 - 1.677
1.527 - 1.538
1.525 - 1.760
1.520 - 1.680
1.520 - 1.550
1.518 - 1.539
1.518 - 1.534
1.518 - 1.526
1.514 - 1.539
1.514 - 1.539
1.510 - 1.532
1.509 - 1.717
1.504 - 1.510
1.502 - 1.520
1.500 - 1.703
1.500 (iso)
1.497 - 1.544
1.496 - 1.519
1.496 - 1.505
1.495 - 1.528
1.494 - 1.504
1.490 - 1.575
1.486 - 1.740
1.483 - 1.487
1.483 - 1.487
1.473 - 1.496
1.464 - 1.507
1.460 - 1.540
1.460 - 1.540
1.450 - 1.520
1.432 - 1.434
1.370 - 1.470
1.37 - 1.39
1.3328
1.327 (iso)
1.0003
0.470 (iso)
0.180 (iso)
 

Notes:
Values may be approximate or may vary by mineral origin and associations with other minerals, inclusions, and by cleanliness and quality of gemstone polish.

(iso) refers to isotropic, meaning that light travels at the same speed in all directions within the gem. These gems have an isometric crystal structure or may be amorphous.

Reference: Color Encyclopedia of Gemstones, Second Edition (1987), by Joel E. Arem.
 

 


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