What is Oldhamite?
Oldhamite is calcium sulfide, a rare meteorite mineral and one of the clearest indicators of highly reducing conditions in enstatite chondrites.
Mineralogy and crystal structure
Reference formula: CaS. Oldhamite is cubic and chemically unstable in moist oxidising environments, where it can alter to sulfates and carbonates. Meteorite context is essential for correct identification. Oldhamite is classified with sulfides and has a cubic crystal system. Typical hardness is 3.5–4 on the Mohs scale and specific gravity is approximately 2.5–2.6.
Colour, lustre and habit
Typical colours include grey, brown, yellow, black. The usual granular, massive, crystalline habit and resinous, sub-metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Oldhamite forms in or is associated with enstatite chondrites and exceptionally reducing meteorite parent bodies. Important documented localities include Enstatite meteorites from Antarctica, India and curated meteorite collections.
A sulfide from an oxygen-poor asteroid
Oldhamite is a time capsule from a very different chemical world. Its calcium-sulfide lattice reveals meteorite formation under oxygen-poor conditions unlike most terrestrial rocks.
Collecting and care
Keep sealed and dry; avoid water, acids and dust, and do not handle as a loose powder.
