This sample of pyrrhotite (formed with quartz) is displayed in the Smithsonian Museum of Natural History. Pyrrhotite is a sulfide mineral of iron with the designated composition Fe1-xS . This sample is about 6x10 cm and is from Trepca mine, Srbija, Yugoslavia.
This sample is about 6x9 cm and is from the same mine. It is also formed with quartz.