The relationship between euhedral and framboidal pyrite in base-metal sulphide ores

Summary Specimens of layered baryte containing a range of pyrite forms, including framboids, framboidal aggregates, spherulites, polyhedra, and zoned euhedral crystals from Kempfield, New South Wales, Australia, have been examined by mineragraphy, X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron-probe microanalysis (EPMA). These investigations showed that the pyrite occurred in two forms—an arsenical variety containing approximately 5% arsenic in solid solution within the pyrite and a non-arsenical variety. EPMA studies indicate that the framboids and the cores of the zoned euhedral crystals have similar levels of arsenic and a genetic relationship is deduced to exist between these forms.