Marcasite and Pyrite (FeS2)

Abstract

We first describe the structures of FeS2-marcasite and FeS2-pyrite, and the way in which they are related. It is then explained how this relationship can successfully account for several phenomena: pyrite- marcasite intergrowths, the reported anisotropy of (nominally cubic, and therefore isotropic) FeS2-pyrite, stacking and deformation faults in pyrite parallel to {100}, and the observed structure of the pararammelsbergite polymorph of NiAs2.