A monoclinic mineral, NaAl₂(AlSi₃)O₁₀(OH)₂; mica group; pseudohexagonal with basal cleavage; forms fine-grained, massive, scaly aggregates; occurs in metamorphic rocks and in soils; not common as it is incompatible with potassium feldspar (albite plus muscovite is more stable); rarely identified because of its similarity to muscovite.