Pyrite is an iron disulphide (FeS2), a common and widespread mineral, mined in many places as an iron ore. It has the cubic crystal system, and well-developed crystals of pyrite can be perfect cubes (hexaeders) with smooth metallic surfaces. The cubes are often intergrown, varying in size from a few mm to over 120 mm. In this example they are embedded in the volcanic host rock in which they formed during a lengthy crystallisation period. Origin of sample is the Victoria mine in Navajun, Spain. Actual width is 27 cm.