Pyroxene-ideal Thompson R M, Downs R T American Mineralogist 89 (2004) 614-628 Model pyroxenes II: Structural variation as a function of tetrahedral rotation model protopyroxene after Yang et al. (1999) with O3-O3-O3 angle = 165.9 and model oxygen radius = 1.306 Note: Atoms Mg, Si, and O are assigned to atomic positions for convenience _database_code_amcsd 0003523 9.154 8.981 5.185 90 90 90 Pbcn atom x y z Mg 0 1/12 3/4 Mg 0 .25 1/4 Si .3082 1/12 1/12 O1 .1335 1/12 1/12 O2 .3665 .25 .1191 O3 .3665 -.0179 .3155