Glaucophane

Glaucophane is a silicate with composition Na₂(Mg,Fe)₃Al₂Si₈O₂₂(OH)₂. It contains six of the "big-8" elements of the Earth's crust. The sample above is about 18x15 cm and is from Valley Ford, California. It is formed with with apatite and chlorite. The sample is on display in the Smithsonian Museum of Natural History.