mica

Any of a group of silicate minerals that split easily into thin flakes along lines of weakness in their crystal structure (perfect basal cleavage). They are glossy, have a pearly lustre, and are found in many igneous and metamorphic rocks. Their good thermal and electrical insulation qualities make them valuable in industry.

Their chemical composition is complicated, but they are silicates with silicon–oxygen tetrahedra arranged in continuous sheets, with weak bonding between the layers, resulting in perfect cleavage.

A common example of mica is muscovite (white mica), KAl₂Si₃AlO₁₀(OH,F)₂.