Pyroxene-ideal
Thompson R M, Downs R T
American Mineralogist 88 (2003) 653-666
Model pyroxenes I: Ideal pyroxene topologies
Pyroxene #7 based on stacking sequence ABABACAC
Note: Atoms Mg, Si, and O are assigned to atomic positions just for convenience.
_database_code_amcsd 0003003
13.063945 6 3.4641016 90 90 90 P2_1ca
atom    x     y     z
SiA 31/32 11/12 11/12
SiB 29/32  5/12   3/4
Mg1a 5/16  1/12  5/12
Mg2a 5/16   3/4  5/12
SiC  5/32  1/12   3/4
SiD  7/32  5/12  1/12
Mg1b 1/16  5/12  5/12
Mg2b 1/16   .25 11/12
O1A   7/8 11/12 11/12
O2A     0   3/4   3/4
O3A     0  1/12   3/4
O1B     0  5/12   3/4
O2B   7/8  7/12 11/12
O3B   7/8   3/4  5/12
O1C   .25  1/12   3/4
O2C   1/8   3/4  1/12
O3C   1/8  1/12  1/12
O1D   1/8  5/12  1/12
O2D   .25   .25   1/4
O3D   .25  5/12   3/4