Pyroxene-ideal
Thompson R M, Downs R T
American Mineralogist 88 (2003) 653-666
Model pyroxenes I: Ideal pyroxene topologies
Pyroxene #21a based on stacking sequence ABABCACBCBAC
Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience.
_database_code_amcsd 0003026
19.595917 6 3.4641016 90 90 90 P2_1cn
atom     x   y   z
SiA   1/48 2/3   0
SiB   1/16 1/6 1/6
Mg1a   1/8 2/3 1/3
Mg2a   1/8   0 1/3
SiC   3/16 1/3   0
SiD  11/48 5/6 1/6
Mg1b  7/24 1/6 1/6
Mg2b  7/24   0 2/3
SiE  17/48 5/6 1/6
SiF  19/48 1/3 1/3
Mg1c 11/24 2/3   0
Mg2c 11/24   0   0
O1A   1/12 2/3   0
O2A      0   0 2/3
O3A      0 2/3 2/3
O1B      0 1/6 1/6
O2B   1/12   0   0
O3B   1/12 1/3   0
O1C    .25 1/3   0
O2C    1/6   0 2/3
O3C    1/6 1/3 2/3
O1D    1/6 5/6 1/6
O2D    .25   0   0
O3D    .25 2/3   0
O1E   5/12 5/6 1/6
O2E    1/3   0 1/3
O3E    1/3 2/3 1/3
O1F    1/3 1/3 1/3
O2F   5/12   0 2/3
O3F   5/12 1/6 1/6