The Natural Formation and Occurrence of Green Quartz
How amethyst under certain conditions may turn green rather than the expected citrine-yellow.
Artificially Induced Colour in Amethyst-Citrine Quartz
A new and rather unusual gem material and possible treatments are discussed.
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.