The perfect cleavage of this mineral allows it to be split into very thin flexible sheets. It is the most common of the mica group minerals and is typically found occurring as "books." The name was used as early as 1794 by Johann Gottfried Schmeisser in his System of Mineralogy and is derived from the term "Muscovy glass," which was a substitute for glass.

Mineral Photos courtesy of R.Weller/Cochise College