muscovite mica from a pegmatite near Coronel Murta, Minas Gerais, Brazil - display specimen

muscovite mica        KAL3Si3O10(OH)2 Coronel Murta, Minas Gerais, Brazil    Muscovite is a common rock-forming mineral. In pegmatites, which are essentially giant-crystal granitic rocks, muscovite forms large books and can be cleaved into large sheets.  It is mined commercially for use as an insulator in transformers and electrical equipment. Scrap muscovite, small flakes, is used as a filler or extender in paints. Transparent in thin sheets, muscovite is flexible and also elastic - it springs back when released. The large crystals of pegmatites form in the final stages of the crystallizing of a magma. As crystallization progresses and various minerals are removed from the melt, the magma becomes more and more water-rich. This allows atoms to move around rapidly and allows the formation of large crystals. These “mother liquors” are often injected into fissures above the magma chamber to form pegmatite dikes. The name muscovite was first used in 1794 in A System of Mineralogy by Johan