The compositional ranges of Mn-pyroxenoids

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Mn-pyroxenoids and clinopyroxenes from Japan were analysed using EDS. Pyroxmangite is extant under 10 % of CaSiO_3 mole, and only Ca-poor one is stable at higher temperatures. The compositional range of FeSiO_3 mole varies widely and reaches 32 mole % among studied pyroxmangites. Rhodonite may be stable under the wide temperature range, and its compositional range exsists between 10 % and 20 % of CaSiO_3 sole and under 30 % of (Fe. Mg)SiO_3 mole. Rhodonite accompanying johannsenite formed under low temperature is high-calcian, and its CaSiO_3 mole reaches about 35 %. Bustamite has wide compositional range located within the area between 30 % and 55 % of CaSiO_3 mole and under 20 % of (Fe. Mg)SiO_3 mole. In case of high temperature, bustamite is stable in the compositional area of clinopyroxene under 20 % of (Fe. Mg)SiO_3 mole. The decreasing temperature invites the appearance of johannsenite near CaMnSi_2O_6, and the distribution of clinopyroxenes on Ca(Fe, Mg)Si_2O_6- CaMnSi_2O_6 join becomes consecutive. That is, the stability field of bustamite is limited at lower temperatures. but it is able to exist outside of clinopyroxene area.