A tentative phase diagram for the system FeS-FeS 2 shows the pyrite-pyrrhotite solvus termination downward at a nearly isothermal phase boundary near 315 degrees C. Above this boundary, hexagonal pyrrhotite has a supercell in which a=2A, c=7C, not previously recognized. Immediately below this boundary, hexagonal pyrrhotite (supercell with a=2A, c=5C) occupies most of the field between 46.6 and 50 percent Fe. This field decreases downward, between a narrow two-phase field with monoclinic pyrrhotite (stoichiometric Fe (sub ) S 8 ) on one side, and a low-temperature (<140 degrees C) two-phase field with troilite on the other. The numerous processes that may affect the composition of pyrrhotite with pyrite limit the reliability of the pyrrhotite geothermometer.

First Page Preview

First page PDF preview
You do not currently have access to this article.