Citation: Thompson, R. M.; Downs, R. T. (2004). Model pyroxenes II: Structural variation as a function of tetrahedral rotation model protoenstatite at 1360 K after Yang and Ghose (1995) with O3-O3-O3 angle = 168.4 and model oxygen radius = 1.321 Note: Atoms Mg, Si, and O are assigned to atomic positions for convenience. American Mineralogist, 89, pp. 614-628.