REFRACTIVE INDEX
The refractive index expresses the ratio between the speed
of light in air and speed through the stone.
Example:
Each stone has its own refractive index. It has a diagnostic
value: it can identify a gemstone. The measurement of this index can be done
using a "refract meter" optical instrument convenient and accurate,
and the method of immersion, which involves placing a stone in a liquid which
is known the refractive index. If the index of the liquid is identical to that
of the stone, the outlines of the stone will become invisible, like the ice is
when immersed in water.
Refractive index of gems and minerals
|
Gem / Mineral
|
Index
|
|
Agate
|
1544-1553
|
|
Alexandrite
|
1745-1759
|
|
Almandine
|
1.76-1.83
|
|
Amazonite
|
1.52
|
|
Amber
|
1.54
|
|
Amethyst
|
1544-1553
|
|
Andalusite
|
1641-1648
|
|
Andradite
|
1.82-1.89
|
|
Apatite
|
1.63-1.640
|
|
Aquamarine
|
1577-1583
|
|
Aventurine
|
1544-1533
|
|
Azurite
|
1.73-1.838
|
|
Beryl
|
1.577-1.60
|
|
Brazilianite
|
1603-1623
|
|
Calcite
|
1486-1658
|
|
Chalcedony
|
1.53-1.539
|
|
Chrysoberyl
|
1.74
|
|
Chrysocolla
|
1.50
|
|
Chrysoprase
|
1534
|
|
Citrine
|
1.55
|
|
Cordierite
|
1.54
|
|
Corundum
|
1766
|
|
Demantoid
|
1.88
|
|
Diamond
|
2417-2419
|
|
Diopside
|
1.68-1.71
|
|
Dolomite
|
1503-1682
|
|
Dumortierite
|
1686-1723
|
|
Emerald
|
1576-1582
|
|
Euclase
|
1652-1672
|
|
Fluorite
|
1434
|
|
Gaylussite
|
1517
|
|
Grossular
|
1738-1745
|
|
Hauynite
|
1502
|
|
Hematite
|
2.94-3.22
|
|
Hessonite
|
1745
|
|
Iolite
|
1548
|
|
Ivory
|
1.54
|
|
Jadeite
|
1.66-1.68
|
|
Kunzite
|
1.655-1.68
|
|
Kyanite
|
1715-1732
|
|
Labradorite
|
1565
|
|
Lapis
|
1.50
|
|
Lazulite
|
1615-1645
|
|
Leucite
|
1.5085
|
|
Malachite
|
1655-1909
|
|
Nephritis
|
1.60-1.63
|
|
Obsidian
|
1.50
|
|
Oligoclase
|
1539-1547
|
|
Olivine
|
1.67
|
|
Onyx
|
1486-1658
|
|
Opal
|
1.45
|
|
Orthoclase
|
1525
|
|
Periclase
|
1.74
|
|
Peridot
|
1.65-1.69
|
|
Pyrope
|
1.74
|
|
Quartz
|
1.55
|
|
Rhodisite
|
1.69
|
|
Rhodochrosite
|
1.60-1.82
|
|
Rhodolite
|
1.76
|
|
Rhodonite
|
1.73-1.74
|
|
Ruby
|
1.76-1.77
|
|
Rutile
|
2.61-2.90
|
|
Sapphire
|
1.76-1.77
|
|
Scapolite
|
1.54-1.56
|
|
Serpentine
|
1.56-1.57
|
|
Sodalite
|
1483
|
|
Spessartite
|
1.81
|
|
Sphene
|
1.885-2.05
|
|
Spine
|
l1712-1736
|
|
Spodumene
|
1.65-1.68
|
|
Tanzanite
|
1.691-1.70
|
|
Thomsonite
|
1.53
|
|
Topaz
|
1.62-1.627
|
|
Tourmaline
|
1624-1644
|
|
Turquoise
|
1.61-1.65
|
|
Uvarovite
|
1.87
|
|
Variscite
|
1.55-1.59
|
|
YAG
|
1.83
|
|
Zircon
|
1.90-2.01
|
|
Zoisite
|
1695
|
|
|
|
Some liquids used for the method of immersion
|
Liquid / Gem
|
Refractive index
|
|
Turpentine / Opal
|
1.47
|
|
Oil minerals / Sodalite
|
1.48
|
|
Benzene / Obsidian
|
1.50
|
|
Cedar oil / Petalite
|
1.51
|
|
Oil of cloves / Iolite
|
1.54
|
|
Nitrobenzene / Quartz
|
1.55
|
|
Bromophorme / Emerald
|
1.59
|
|
Carbon disulfide / Tourmaline
|
1.63
|
|
Monobromonaphtalène / Spodumene
|
1.66
|
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