Pyrrhotite
Pyrrhotite is a slightly iron-deficient iron sulfide, often magnetic, found in carbonaceous chondrites and Martian meteorites.
Pyrrhotite is an iron sulfide closely related to troilite, but with a few iron atoms missing from its crystal structure, giving formulas from about Fe7S8 to FeS. Those gaps make many forms of pyrrhotite magnetic, unlike troilite.
In meteorites, pyrrhotite is common in CM, CI, CR and CK carbonaceous chondrites and in samples returned from Ryugu, often alongside pentlandite. Its slight iron shortage is a sign that it formed in more oxidising conditions than the troilite of ordinary chondrites. Pyrrhotite is also the main sulfide in Martian shergottites and nakhlites, where it reflects the chemistry of Martian magmas.
Because magnetic pyrrhotite can record ancient magnetic fields when it forms or is heated, it is of interest to scientists studying whether early asteroids and Mars had magnetic dynamos. On a polished surface it looks creamy pink-brown in reflected light.
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