Citrine is a variety of quartz whose color ranges from a pale yellow to brown. Natural citrine is rare; most commercial citrines are heat-treated amethyst. Citrine contains traces of The name is derived from Latin, citrina, which means "yellow".
Elbaite, on Quartz, nicknamed "Rabbit Ears". Amazing natural crystal formation ~ Houston Museum of Natural Science, Cullen Hall of Gems and Minerals (photo credit: Houston Convention and Visitor's Bureau)
Unique crystal of small green Apatite (analyses indicated Fluorapatite) on two faces of a complete, well terminated Tanzanite crystal. I have seen Tanzanite spcimens with Apatite on the Graphite matrix, but never one with Apatite on the Tanzanite crystal.