Pyroxene-ideal Thompson R M, Downs R T American Mineralogist 88 (2003) 653-666 Model pyroxenes I: Ideal pyroxene topologies Pyroxene #18 based on stacking sequence ABABACBABABC Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience. _database_code_amcsd 0003021 19.595917 6 3.4641016 90 90 90 P2_1cn atom x y z SiA 1/16 1/6 1/3 SiB 1/48 2/3 1/6 Mg1a 1/8 2/3 1/2 Mg2a 1/8 0 1/2 SiC 3/16 1/3 1/6 SiD 11/48 5/6 1/3 Mg1b 7/24 1/6 0 Mg2b 7/24 0 1/2 SiE 17/48 5/6 0 SiF 19/48 1/6 1/3 Mg1c 11/24 2/3 5/6 Mg2c 11/24 0 5/6 O1A 0 1/6 1/3 O2A 1/12 0 1/6 O3A 1/12 1/3 1/6 O1B 1/12 2/3 1/6 O2B 0 0 5/6 O3B 0 2/3 5/6 O1C .25 1/3 1/6 O2C 1/6 1/2 1/3 O3C 1/6 1/6 1/3 O1D 1/6 5/6 1/3 O2D .25 0 1/6 O3D .25 2/3 1/6 O1E 5/12 5/6 0 O2E 1/3 0 5/6 O3E 1/3 2/3 5/6 O1F 1/3 1/6 1/3 O2F 5/12 0 1/2 O3F 5/12 1/6 0