Mica is also known as muscovite (hydrated aluminum potassium silicate) which is the most common type of mica derived from ideal talc and pyrrophilite in environments containing aluminum, potassium, sodium or calcium ions. Aluminum removes 25% of tetrahedral silica in the structure and potassium ions are placed between the sheets to maintain electrical neutrality. The bonds between muscovite sheets are weaker than internal bonds as evident from its perfect cleavage in one direction. However, the bonds are stronger than those in pyrrophilite and thus muscovite is not greasy. Muscovite is formed as primary igneous mineral in granites and high-silicon rocks and most metamorphic rocks. It is also a major component of sedimentary schist.