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Biotite series (Photo) [abbr. Bt ]

Year of discovery: 1891 (Japan)

Locality list: 2,489 localities of biotite

• [K][ A²⁺₂ ][ B ][(OH)₂|Al X Si₂O₁₀]

• Alter to Vermiculite.
• Substitution pseudomorph: Replace Staurolite.

• [ Fe ][ Fe²⁺ ][ Si⁴⁺ ]: Annite
• [ Mg ][ Mg²⁺ ][ Si⁴⁺ ]: Phlogopite
• [ Fe ][ Al³⁺ ][ Al³⁺ ]: Siderophyllite
• [ Mg ][ Al³⁺ ][ Al³⁺ ]: Eastonite

• Class: Trioctahedral < True mica group < Mica supergroup

• System: Monoclinic (1M, 2M₁) (Layer-stacking polytype)