Pyrite

About Pyrite

An iron sulfide famous as fools gold for its brassy metallic luster. Its name comes from the Greek word for fire, because it gives off sparks when struck against steel. It often forms near perfect cubes, especially at Navajun in Spain. Much vintage marcasite jewelry is actually set with small cut pieces of pyrite. It was used in early wheellock firearms to produce sparks. In humid air it can slowly decay, releasing sulfuric acid.