Structure refinement of a nonstoichiometric pyroxene synthesized under ambient pressure

Structure refinement was carried out on a nonstoichiometric clinopyroxene grown under the ambient pressure from a glass with composition of 23%(mol)Di+53%Es+24%An. The degree of nonstoichiometry in this crystal is significantly larger than those of clinopyroxenes reported previously, which were found in high pressure products. The refinement gave the empirical chemical formula (Ca_0.742Fe_0.087)(Mg_0.016Al_0.888Fe_0.075)(Al_0.500Si_1.500)O₆ for the crystal and showed that vacancies are located mainly at M2 sites. Despite replacement of Si by Al, the crystal has a smaller cell volume than diopside primarily owing to a significant amount of Mg at M1 being replaced by Al. Received: 25 June 1997 / Revised, accepted: 6 September 1997