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The Natural Formation and Occurrence of Green Quartz

How amethyst under certain conditions may turn green rather than the expected citrine-yellow.

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Artificially Induced Colour in Amethyst-Citrine Quartz

A new and rather unusual gem material and possible treatments are discussed.

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Dr E. J. Gübelin Collection Peridot
GIA's Gübelin Gem Project: Various Gems, Olivine - Rutile

Among the collection assembled by Dr Edward Gübelin are a number of uncommon gemstones from many worldwide localities.

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