Annite (Biotite) - KFe²⁺ (Si₃Al)O₁₀(OH)₂

Habit: Brown or black. Tabular to short prismatic crystals and cleavage fragments with pseudo-hexagonal outlines; commonly foliated masses. Adamantine luster; translucent to transparent. Brownish white streak.

Environment: Forms large crystals in granites and granitic pegmatites.

Etymology: Named after Cape Ann, in Essex County, Massachusetts, where it is found. Biotite refers to the dark mica series, which extends from the iron end-member annite to the magnesium end-member phlogopite.