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The Origin and Recovery of Gemstones
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absorption spectrum agate alexandrite almandine aluminium amber America amethyst aquamarine bands beads beryl biaxial birefringence blue brown Burma cabochon calcium called carat carbonate carved cat's-eye cavities Ceylon chalcedony chemical chromium chrysoberyl cleavage colourless copper coral corundum County cultured pearls cut stones demantoid density deposits diamond district double refraction doublet edge emerald extraordinary ray Figure fluorescence garnet gem material gemstones glass glow gravels hardness heat imitation inclusions Indian indices iron ivory jade jadeite jewellery known layer limestone localities luminescence lustre marble massive method mineral mines Mogok Mohs's scale natural nephrite occurs opal ordinary ray ornamental owing oxide oyster pale pebbles pegmatite peridot pieces pink polished prism produced pyrope quartz refractive index river rock crystal ruby rutile sapphire seen shell short-wave silicate specimens spinel surface synthetic spinel table facet topaz tourmaline transparent turquoise ultra-violet light usually varies variety violet x-rays yellow zircon