Zoisite

Zoisite is a silicate of calcium and aluminum with the composition Ca₂Al₃(Si₃O₇)(SiO₄)(O,OH)₂ . The sample above is about 5x5 cm with the crystal having dimension about 3x1 cm. It is from Arusha, Tanzania. These samples are identified as the variety tanzanite and are on display at the Smithsonian Museum of Natural History.

The gem above is 122.7 carats and is from Tanzania. The mineral sample at right is about 2x5 cm and is from Arusha, Tanzania.