Abstract
Though the genetic mechanism of monoclinic pyrrhotite in natural occurrence and its phase equilibrium relations with hexagonal pyrrhotite have not been accurately known yet, two mechanisms of the formation through the inversion from hexagonal pyrrhotite with a descending temperature and of the direct formation as monoclinic pyrrhotite at a low temperature below 320°C from ore solution are supposed. In order to examine the possibility of the former mechanism, monoclinic pyrrhotite was synthesized by means of annealing hexagonal pyrrhotites with various compositions. When synthesized hexagonal pyrrhotites with the seven compositions between 47.39 and 46.08 atomic percent Fe were annealed at 290°C or 300°C for 48 or 96 hours, they were not changed in the composition of 47.39 and 47.17 atomic percent Fe, but monoclinic pyrrhotite was formed by the inversion from hexagonal pyrrhotite in the compositions from 46.95 to 46.08 atomic percent Fe. In the sulfur rich composition such as 46.30 or 46.08 atomic percent Fe, pyrite was found with monoclinic pyrrhotite. On the basis of these data the composition ranges of hexagonal and monoclinic pyrrhotities are discussed.
