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