Spessartine-Andradite In Scapolite Pegmatite, Ilmeny Mountains, Russia

Abstract

An unusual garnet representing a solid solution of spessartine, andradite, and almandine was found in pit no. 287, Ilmeny Mountains (Ilmeny Reserve, Chelyabinsk district, Russia). The garnet occurs in a diopside-quartz-scapolite vein cutting a scapolite-diopside rock which occurs at the contact between a calcite-dolomite carbonatite and pyroxene-scapolite glimmerite. Mossbauer spectroscopy of the garnet indicates ca .46% Fe presentas Fe3+. The chemical composition of the garnet is (wt.%): SiO2 35.45, TiO2 0.91, Al2O3 16.54, Fe2O3 7.52, FeO 7.69, MnO 18.87, MgO 0.81, CaO 11.62, Y2O3 0.99, total 100.40. Its Raman and IR-spectra strongly resemble those of other Mn-rich garnets (especially calderite) and therefore they should not be used as a sole analytical technique in garnet species identification. The solid solution of andradite and spessartine is known under the acronym “spandite” in old literature.