Mineral Species: Pyrrhotite

Chemical Formula: FeS

Chemical Name: Iron Sulfide

Mineral Class: Sulfide

Mineral Notes: Pyrrhotite is an unusual mineral with some fascinating properties. First, it has an unusual composition. The amount of Sulphur varies widely, by anything between 20% or 50%. Thus the correct formula is Fe1-xS. Secondly it has two crystal symmetries. When low in Sulphur the structure is hexagonal. When high, it is monoclinic. Usually such differences would result in classification as two separate minerals. However single Pyrrhotite crystals can contain both phases. And finally the mineral is one of the few that are magenetic.