Mn-Ca sulfide, (Mn,Ca)S, is a pale to dark brown accessory mineral found in minor amounts in highly reduced meteorites such as many enstatite chondrites, and some aubrites and enstatite achondrites. Oldhamite in enstatite chondrites likely formed by solar nebular gas condensation.

CaS Oldhamite was also found in the most fresh Sutter’s Mill meteorites (those that were not rained upon after the fall) and is the result of the mineralogical transformation of calcite (CaCO3) to oldhamite (CaS) and portlandite [Ca(OH)2] during extraterrestrial thermal metamorphism on the Sutter’s Mill parent body.

CaS Oldhamite is a water soluble mineral, and therefore easily lost and converted to Ca-rich weathering materials once the meteorite has been rained on or has become saturated with water (terrestrial aqueous alteration).