The Mica group has a unique and defining physical characteristic: the ability for individual crystals to easily cleave (or split) into extremely thin elastic plates or sheets. This is called basal cleavage (basal: only one cleavage plane). Micas are significant rock forming minerals being found in all three rock types: igneous, metamorphic and sedimentary. There are numerous minerals in the Mica group, but the three most common and known to collectors are Muscovite, Biotite and Lepidolite. All three have the same cleavage, vitreous to pearly luster and monoclinic crystal system.
Muscovite is the most common of the three. It is typically yellow, silver, grey and white. Crystal forms include pseudohexagonal, tabular, thick rosettes, botryoidal, globular and twinned crystals forming five-point stars called “Star Muscovite.” Notable locations include Brazil, China, Namibia and Pakistan.
Biotite is typically black to dark brown. Crystal forms include pseudohexagonal, tabular, prismatic barrel-shaped and rounded aggregates of dense crystals. Notable locations include Canada, Germany and Portugal.
Lepidolite is typically pink to purple. Crystal forms include massive, dense scaly aggregates, pseudohexagonal, tabular and flaky. Also found as an outer zone around interior Muscovite for a very aesthetic presentation. Notable locations include Brazil, Afghanistan, and the USA (California).