Muscovite
Muscovite (also known as common mica, isinglass, or potash mica) is a phyllosilicate mineral of aluminium and potassium with formula KAl2(AlSi3O10)(F,OH)2, or (KF)2(Al2O3)3(SiO2)6(H2O). It has a highly perfect basal cleavage yielding remarkably thin laminæ (sheets) which are often highly elastic. Sheets of muscovite 5 m × 3 m have been found in Nellore, India.