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 Johann Gottfried Schmeisser, derived from an earlier name, Muscovy-glass, a name given to it in Elizabethan England from its use in Medieval Russia as a cheaper alternative to glass in windows.  It is the most common mica.

Coronel Murta is a municipality on the left bank of the Jequitinhonha River in the northeast of the state of Minas Gerais. It is famous for the minerals mined from pegmatites.

Both sides of this specimen are shown. The pencil is 5 1/2" long for scale.

Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.

Shipping: By Priority Mail or USPS Ground Advantage, whichever is cheaper, unless we find a better rate. Click > here < for shipping rates. See comment at Note! Use back button to return to this page.