| Crystal lattice parameter (Guinier analyses), habit type (SEM), optical anisotropy (apparent angle of rotation A;Two distinct formational mechanisms for nucleation of pyrite were recognized, resulting in distinct sequences of crystal habits: (1) micron-sized pyrite cubes that nucleated in an orientation perpendicular to the precursor pyrrhotite surfaces, and were subsequently overgrown by cubo-octahedral pyrite crystals, and (2) micron-sized cubes with distinct hopper morphology that nucleated at the exterior of native liquid sulfur droplets, and subsequently were engulfed by pyritohedral crystals.;The pyrite crystals of sequence (1) appear to have formed by utilizing H;The relationships between formational mechanisms and properties among pyrite types appear to be directly related to the S-S bond distance of the "substrate" on which pyrite crystals nucleate. Pyrite crystals formed on sulfur droplets may have inherited a disulfide group characterized by strong covalent bonding and short S-S bonds of the polysulfides. The short S-S bond is reflected by the smaller lattice parameter of the pyrite. In contrast, pyrite crystals that grew after oriented nucleation on pyrrhotite seem to have incorporated the sulfur atom arrangement in the pyrrhotite substrate, that has a larger S-S bond and lesser covalent bonding than in the disulfide group. The large S-S bond correlates with the larger lattice parameter of the pyrite. |
