Abstract
Four stable pyroxene polymorphs have been identified: Ca-rich clinopyroxene (Ca-rich Cpx, space group: C2/c), Ca-poor clinopyroxene (pigeonite) (Ca-poor Cpx, C2/c, P21/c), protoenstatite (Pen; Pbcn), and low-temperature orthopyroxene (LTOpx, Pbca). Moreover, Ohi et al. (2008, 2010) established the stability field of high-temperature orthopyroxene (HT-Opx, Pbca) in enstatite (Mg2Si2O6) - diopside (CaMgSi2O6) system. However, LT- and HT-Opx have never been reported in natural sample. Micrometeorite which has about 100 um in size is collected from the ice in Antarctica. The most of them is like to be condritic meteorite and consistent with olivine, pyroxene and so on. Two types of Opx which have the different chemical composition although the same space group (Pbca) are found in a micrometeorite, TT001c5-48.
