MICA minute #17 from MICA Watches on Vimeo.
Mica is really a whole host of minerals, muscovite, biotite and chlorite being the most common. Mica is soft and can be distinghed by it perfect cleavage, which means the mineral breaks into very thin sheets. It is easily eroded to form clay minerals. Mica is abundant in silicic igneous rocks and is the main component of many metamorphic rocks (add enough heat and pressure to clay and it becomes mica). Schist is a metamorphic rock composed almost entirely of mica.