A dioctahedral member of the true mica group. The end-member formula is KAl₂ vAlSi₃O₁₀(OH)₂ (where v = vacancy). Typical range in composition is: Si= 3.0 – 3.1, ^ivAl = 1.9 – 2.0, K = 0.7 – 1.0 (although the interlayer site is defined in true micas as I ≥ 0.85), ^viR²⁺/(^viR²⁺ + ^viR³⁺) < 0.25, ^viAl/(^viAl + ^viFe³⁺) = 0.5 – 1.0 (Rieder et al., 1998). Muscovite commonly occurs in the 2M₁ polytype, and less commonly in 1M, 3T, 1M_d, and 2M₂ forms. Muscovite is a common rock forming mineral and occurs in igneous, metamorphic, diagenetic, and weathering environments.
Cf., nanpingite, paragonite