Pyrrhotite

Iron sulfide group of minerals whose composition ranges widely between its end members pyrrhotite (Fe₇S₈) whose crystal structureMutual arrangement of atoms, molecules or ions that are packed together in a crystal lattice to form a crystal. is monoclinic, and troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. (FeS) whose crystal structure is hexagonal. Its general formula is Fe_1−xS (where x = 0 to 0.17). The troilite phase is found mainly in meteorites and in the sulfide melts produced by the meteoritic impact like those found around the Sudbury impact structure¹. The magnetic properties of pyrrhotite are due to the iron vacancies in the crystal structure. The greater the number of Fe vacancies, the stronger the magnetic susceptibility. This deficiency results from the substitutionReplacement of one ion or ionic group for another in the same structural site in a mineral yielding a solid solution. Most substitution in minerals is of cations which are smaller and essentially sit in a lattice of oxygen anions. Anionic substitution does occur in halides. Substitutions are classified based 3Fe²⁺ ↔ 2Fe³⁺ + o (where o is an iron vacancyUnoccupied sites within a crystal that are usually occupied by an atom. A vacancy may move when a neighboring atom or ion moves to occupy the vacant site (the vacancy shift in the opposite direction to the site that was the source of the atom). The surrounding bonded crystal structure). Since troilite has no vacancies, it is not magnetically susceptible while monoclinic pyrrhotite is the most magnetically susceptible.

When referring to pyrrhotite, meteoriticists most often mean Fe-deficient (x > 0), and when they say troilite, they mean stoichiometricPertaining to or involving substances that are in the exact proportions required for a given reaction. (x = 0 so that Fe²⁺ + S^2- combine to form FeS). If an analysis is not provided, meteoriticists are usually just assuming the mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous is what is normal for that meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and type. Note that troilite  may be referred to as 2C pyrrhotite, while Fe₇S₈ may be referred to as 4C pyrrhotite in some literature.

Pyrrhotite has been found as an accessory mineralConstituent mineral present in small quantity and not taken into account in identifying or classifying a rock.   in some carbonaceous chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such (TBD)², R chondrites (TBD)³, ordinary chondrites (Soko-Banja (LL4))⁴, shergottitesIgneous stony meteorite with a Martian origin consisting mainly of plagioclase (or a shocked glass of plagioclase composition) and pyroxene. They are the most abundant type of SNC meteorites and the type member is the Shergotty meteorite, which fell in India in 1865. Shergottites are igneous rocks of volcanic or (Tissint)⁵, nakhlites (Nakhla, and Governador Valadares)⁶ , irons (Bocaiuva)⁷ and within troilite nodules in many other iron meteorites, and other meteorites.