Mica refers to a group of silicate minerals distinguished by their unique physical property of perfect basal cleavage. This characteristic allows individual crystals to be easily split into thin, fragile, and elastic plates.
These minerals are commonly found in igneous and metamorphic rocks, though they occasionally appear as small flakes within sedimentary rock formations. Mica is particularly prominent in schists, granites, and pegmatites; notably, "books" of mica spanning several feet across have been discovered in some pegmatite deposits.