NEW DATA ON STANNITE

Abstract

Numerous investigations of natural and synthetic stannite have led to the conclusion that there are five modifications of this mineral. Two are cubic, a low-temperature modification stable at up to 565° C, and a high-temperature, existing above 709° C. The other three are a high-temperature tetragonal synthetic, stable from 565° to 709° C, a tetragonal synthetic, quenched from 800°, and the natural modification. These three differ slightly from each other in their X-ray patterns. On its DTA and DDTA curves our synthetic tetragonal stannite did not always show a thermal reaction at 706° C, which, according to published information, marks the polymorphous transition of the tetragonal modification to the cubic. Where this reaction has been recorded, it was at 709° ± 3° C. The results of thermal analysis confirm the conclusion, based on comparison of X-ray and microdiffraction data that there is only one stannite modification, the tetragonal, which remains stable until it melts. Isostannite is an independent mineral species, similar to stannite but differing from it in composition and structure.