Pyroxene-ideal
Thompson R M, Downs R T
American Mineralogist 88 (2003) 653-666
Model pyroxenes I: Ideal pyroxene topologies
Pyroxene #21b based on stacking sequence ABABCACBCBAC
Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience.
_database_code_amcsd 0003027
19.595917 6 3.4641016 90 90 90 P2_1cn
atom    x   y   z
Mg1a 1/24 2/3 1/3
Mg2a 1/24 1/2 5/6
SiA  5/48 1/6 1/6
SiB  7/48 2/3   0
Mg1b 5/24 1/6 5/6
Mg2b 5/24   0 1/3
SiC 13/48 2/3 1/3
SiD  5/16 1/3   0
Mg1c  3/8 2/3   0
Mg2c  3/8   0   0
SiE  7/16 1/3 1/3
SiF 23/48 5/6 1/6
O1A   1/6 1/6 1/6
O2A  1/12   0   0
O3A  1/12 1/3   0
O1B  1/12 2/3   0
O2B   1/6   0 2/3
O3B   1/6 2/3 2/3
O1C   1/3 2/3 1/3
O2C   .25   0   0
O3C   .25 2/3   0
O1D   .25 1/3   0
O2D   1/3   0 1/3
O3D   1/3 1/3 1/3
O1E   1/2 1/3 1/3
O2E  5/12   0 2/3
O3E  5/12 1/3 2/3
O1F  5/12 5/6 1/6
O2F   1/2   0 1/3
O3F   1/2 2/3 1/3