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Iron sulfide mineral in which the ratio of iron to sulfur atoms is somewhat variable but is always slightly less than 1. It commonly is found in association with other sulfides. The variety troilite, with a composition near that of iron sulfide (FeS), is an important constituent of some meteorites.
This entry comes from Encyclopædia Britannica Concise. For the full entry on pyrrhotite, visit Britannica.com.