System CaO–MgO–Al2O3–SiO2 Saturated with Silica

Abstract

The silica–saturated CMAS system includes assemblages with anorthite, kyanite, and quartz or coesite. Clinopyroxene coexisting with such silica–rich phases can dissolve an excess of silica charge balanced by vacancies in the M2 site. Such “non-stoichiometric” pyroxenes were first reported by Eskola [165] and synthesized by Mao [313]. Other natural occurrences were reported by Smyth [416] and McCormick [317]. The compositions of clinopyroxene with vacancies can be extrapolated to the end–member Ca0.5AlSi2O6. Following Khanukhova et al. [269], Gasparik and Lindsley [2] started to use for this component the name Ca–Eskola pyroxene (CaEs), and reported the synthesis of a pyroxene along the CaTs–CaEs join with up to 40 mol% of CaEs.