This sample of Alexandrite is displayed in the Smithsonian Museum of Natural History. Alexandrite is an oxide mineral of beryllium with the composition BeAl2O4. It is the name given to a gem-quality variety of chrysoberyl. This gem at left is 17.08 carats and is named the Whitney Alexandrite. It is from Hematita, Minas Gerais, Brazil and is regarded as one of the finest Alexandrite gems. The crystal is a rare twinned crystal of Alexandrite. It is from the same location and of similar material. It is shown at the same scale.