Mica Transistor Insulators
Mica is a naturally occurring mineral, which is present in most granite rock formations. It occurs as a geological fault between two layers of hard rock. In brief, Mica is a generic term applied to a group of complex alumino-silicate materials, having a plate like structure, with different chemical compositions and physical properties.
One of its main uses is as an electrical and thermal insulator for transistors from heatsinks.