Pyrite is an iron sulphide (FeS2), one of the most abundant sulphides on earth, used as an iron ore as well as the manufacture of sulphuric acid. It is an abundant mineral that occurs in many types of geological environments and rocks. When crystalline, it may form perfect cubes (hexaeders) with smooth or striated metallic surfaces. Outsiders sometimes mistake it for gold, hence its nickname "fool's gold". The cluster of intergrown pyrite cubes in this specimen measure 45 mm in width.