The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having highly perfect basal cleavage. The five most common Micas are: Phlogopite, Biotite, Zinnwaldite, Lepidolite and Muscovite. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.
Mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites. Until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in
Mica has several industrial uses including “Isinglass Mica” which are sheets of mica used as peepholes in boilers and lanterns because they are less likely to shatter compared to glass when exposed to extreme heat. Mica has a high dielectric strength and excellent chemical stability, making it a favored material for manufacturing capacitors for radio frequency applications. It is also used as an insulator in high voltage electrical equipment.