Cu₃(V₂O₇)(OH)₂.2H₂O

This sample of volborthite is displayed in the Smithsonian Museum of Natural History. Volborthite is an oxide mineral of copper and vanadium with the composition Cu₃(V₂O₇)(OH)₂.2H₂O. The sample at left is about 5x9 cm and is from Monument Valley, Arizona.