The mica classification of rock includes silicates that contain aluminum and peel off in thin, flexible sheets. There are a number of types of mica, but Muscovite and biotite are the most common and easily recognized. Muscovite mica can appear to have various shades of color, and biotite is dark brown, gray or black.
Muscovite mica is usually transparent and lacking in color but can appear yellow, silver, green or brown, depending on what other minerals are present. Its cleavage -- the way the rock naturally breaks -- is considered "perfect" because it can peel off in large sheets. Muscovite has a pearly luster and has a measured hardness of 2 to 2.5 on a scale of 1 to 10 relative to other rock types.
Muscovite mica is found in a variety of igneous (volcanic) and metamorphic (pressure-formed) rocks and with less frequency in sedimentary rocks. It is the most common white mica and is found worldwide. Russia, Pakistan, India and Brazil have the largest deposits of muscovite. Deposits of mica are called books because of the way they peel, separating into sheets resembling book pages. Tape is commonly used to peel large sheets of mica from the rock of origin.
The name "mica" was given to this type of rock because of its luster; "micare" is a Latin word meaning "to shine." All types of mica have a shiny appearance, regardless of the color. Muscovite mica is named for the state of Muscovy, in old Russia, where muscovite was originally used for windows the way glass is used today. While muscovite is rarely used today in its full sheet form for windows, it is used in powdered form in many modern products.
Muscovite mica is used in a variety of industrial products, such as fireproofing materials and electronic parts, as well as for its heat-resistant and insulating properties. It is used in the production of lubricants, as well as in the manufacture of paint to reduce running and promote weather resistance. It is incorporated into makeup, glitter and nail polish to achieve a pearly look and into wallpapers to give them a shiny finish.