Abstract
A sensitive magnetic thermobalance has been constructed and used to study “hexagonal” and monoclinic pyrrhotites. Confusion about magnetism of the former has been cleared up by using different thermal cycles, and hexagonal pyrrhotites may be made magnetic at will. The breakdown temperature of monoclinic pyrrhotite is still uncertain and probably varies with content of impurities, as there seems to be a difference between dry and hydrothermal systems.
Vacancy diffusion in pyrrhotite proceeds rapidly at 200°C, negating the value of structural information as an indicator of temperature or pressure of formation. Reaction occurs with adsorbed water or oxygen at temperatures from less than 350° to 500°C or more.
Experimental evidence has been obtained for solid state exsolution of magnetite, postulated in Part II [Am. Mineral., 57, 1876–1880 (1972)].
