Micas are sheet silicates, historically significant for their ability to be split into large, thin sheets that are uniquely useful for their electrical, thermal and mechanical properties. They have high electrical and thermal insulating properties, are resistant to chemical attack, can be split into transparent or optically flat films, and can be cut or stamped to shape. Most mica used today, however, is in ground form, although the mineral's platy nature, inertness and optical properties are still primary attributes. There are two commercial forms of mica: muscovite, a potassium aluminum silicate KAl2(AlSi3O10)(OH)2, and phlogopite, a potassium magnesium aluminum silicate KMg3(AlSi3O10)(OH)2. The coatings industry uses muscovite nearly exclusively, primarily because it has better color.Because mica plates are generally stronger and less brittle than the particles of certain other high aspect ratio fillers, such as talc, clays, and glass flake, they are more resistant to breakage and reduction in aspect ratio under high-intensity mixing or milling.