Mica is a group of minerals, which belongs to the sheet minerals (phyllosilicates). They form thin, flexible platelets. For refractory purposes the bright mica (muscovite) is used, which is characterised by its high content of potassium (cf. chemical data). Mica indicates a relatively low melting point, so that it can not be used alone, but only in combination with other refractory fillers such as talc or pyrophyllite.