Pyrrhotite composition is conventionally expressed via N(FeS), the Fe:S atomic ratio expressed as a percentage, ranging from 100 (stoichiometric troilite, FeS) down to about 87 for Fe-deficient monoclinic pyrrhotite (Fe7S8).
For Fe7S8, the Fe:S atomic ratio is 7/8 = 0.875, i.e., N(FeS) = 87.5. This is the classic value cited for monoclinic pyrrhotite (Fe7S8), distinguishing...
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