R7: Petrology, Mineralogy and Economic geology (Joint Session with Society of Resource Geology)

[R7-09] Fine structures of omphacite in CaO-Na₂O-CO₂ rich fluid

*Shugo Ohi¹, Shusuke Kinoshita², Yohei Igami², Akira Miyake², Takao Hirajima² (1. Shiga Uni. Education, 2. Kyoto Uni. Science)

Keywords:omphacite, CO2-rich fluid, TEM

Omphacite (Omp) has the chemical composition around (Na_0.5Ca_0.5)(Al_0.5Mg_0.5)Si₂O₆ in diopside – jadeite system. At high temperature, Al and Mg in M2 site and Na and Ca in M1 site are disorder and Omp has C2/c symmetry. If symmetry reduction from C2/c is achieved entirely by cation ordering, possible ordered space groups reduce to P2/n, P2/c, C2 and P2. Among the studies on Omp, however, few have observed Omp with P2/c, C2 and P2 space group except Carpenter (1978, 1980).
In present study, we observed Omp with C2/c, P2/n, P2/c, C2 and P2 space group in three types of Omp microstructures.