Mica Muscovite Mined in Nigeria. The name “Muscovite” comes from the term “Muscovy-glass”, a name formerly given to the mineral because it was actually used in Russia for windows. Muscovite typically occurs in metamorphic rocks, particularly gneiss and schist, where it forms crystals and plates. It also occurs in igneous rocks such as
granites and fine-grained sedimentary rocks. Large crystals of muscovite are often found in veins and in pegmatite.
Muscovite reflects light strongly from broken fragments. This is caused by a natural cleavage resulting in thin sheets (“Basal Cleavage”). Sheets naturally form in alternating layers, resulting in Muscovites distinctive shape. When the sheet growth is unobstructed they form hexagonal sheets. A unique variety in Brazil forms yellow five pointed stars and is called "Star Muscovite".
Muscovite is usually clear but may be silvery, coppery silver, light gray, brown, pale green, or rose-red in color depending on the thickness of the sample and
presence of impurities.