Powellite has the composition CaMoO4, so it is classified as an oxide mineral. This sample of powellite is on a base of stibnite. The element calcium is reasonably abundant, so the presence of molybdenum in this mineral is significant.
This sample is on display in the Smithsonian Museum of Natural History. Its source is listed as the Nasik District, Maharashtra, India. The size of the sample is 2-3 cm.