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Observed phenomena
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conclusion
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Examples
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Gem rotation 360 degrees. Dark
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isotropic---Non crystal,cubic lattice
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Garnet, spinel, man-made glass, natural glass, fluorite, diamond, opal, plastic
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Gem rotation 360 degrees.Four dark and four bright.
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Anisotropy---Uniaxial or biaxial crystal
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Beryl, corundum, topaz, zircon, tourmaline, quartz, olive green, gold emerald, tanzanite
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Gem rotation 360 degrees.Bright.
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Multi crystal
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Jade,nephrite jade, agate, chalcedony
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Double-crystal spectrometry
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Sapphire, bicrystal
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Some two layers of stone
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Sapphire,Synthetic ruby two layers of stone
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Reflection anomaly
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Fluorite cleavage
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Gem display extinction anomaly
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Strain anisotropy,Often appear in other aspects of isotropic materials
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Man-made glass, natural glass, fluorite, Werner Ye synthetic pointed stone, iron and aluminium garnet, diamond, amber
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