The biotite subgroup includes:
annite:
KFe2+3(AlSi3O10)(OH)2
fluorannite:
KFe2+3(Si3Al)O10sF2
fluorophlogopite:
KMg3(Si3Al)O10F2
phlogopite:
KMg3(AlSi3O10)(OH)2
siderophyllite:
KFe2+2Al(Si2Al2)O10(OH)2
tetraferriphlogopite:
KMg3(Si3Fe3+)O10(OH)2
The biotite subgroup is a member of the trioctahedral mica group
of the mica group.
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