GIA Gem Project
Various Gems (Olivine - Rutile)
Among the collection assembled by Dr. Edward Gübelin are a number of uncommon gemstones from many worldwide localities.
The Natural Formation and Occurrence of Green Quartz
How amethyst under certain conditions may turn green rather than the expected citrine-yellow.
Artificially Induced Color in Amethyst-Citrine Quartz
A new and rather unusual gem material and possible treatments are discussed.