A natural mineral, a silicate of several oxides; muscovite. It is used as an insulator and dielectric. Its resistance per centimeter cube after several minutes electrification at 20º C. (68º F.) is 8.4E13ohms (Ayrton). Its specific inductive capacity is 5, air being taken at 1.

Mica  is a common mineral found in rocks in many parts of the world. It is mined in India, Canada, North Carolina and South Dakota. Several varieties occur (muscovite, biotite, etc.)—valuable only when found in large sheets which can be split smoothly. Transparent sheets are used for lamp chimneys and stove doors. It is also employed in electrical work, and lubricating. Some is imported from India.