AM_Biotite_1 Formula: Mg2.001 Al1.999 K Si3 O12 H2 Name: Biotite Unit cell: 5.331 9.231 10.173 90.0 100.16 90.0 , V=492.77 Space group: C12/M1 (12)

Takeda H , Ross M , American Mineralogist , 60 (1975) p.1030-1040, Mica polytypism: Dissimilarities in the crystal structures of coexisting 1M and, 2M1 biotite