AM_Biotite_2 Formula: Mg2.001 Al1.999 K.5 Si3 O12 Name: Biotite Unit cell: 5.329 9.234 20.098 90.0 95.09 90.0 , V=985.08 Space group: C12/C1 (15)

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