Synthesis of pyroxenoids and pyroxenes in the system MnSiO3-MgSiO3-CaSiO3 with excess quartz

Synthesis experiments in hydrothermal cold seal bombs were performed at 700 degreesC (0.2 and 0.5 GPa) and 900 degreesC (0.2 GPa) using MnO2-MgO-CaO-S iO2 mixtures and further runs at higher pressure (1.5 and 2 GPa) were perfo rmed in a piston cylinder apparatus. Run products were the pyroxenoids rhod onite, pyroxmangite and bustamite, the clinopyroxenes kanoite and manganoan diopside and the amphibole manganoan cummingtonite. In the 700 degreesC ru ns pyroxmangite is often formed as a metastable product. The coexistence of rhodonite and kanoite results in three-phase fields for rhodonite-kanoite- pyroxmangite and rhodonite-kanoite-bustamite, Transmission electron microsc ope (TEM) data showed that the pyroxenoids are always intergrown, even in t he 900 degreesC runs. This limits the application of a previously suggested rhodonite-pyroxmangite geothermometer. The formation of a nine-fold chain silicate was observed with TEM at approx. Mn0.6Mg0.4SiO3 composition.