Mica is a name given to aluminum-containing silicates which cleave in thin sheets. The micas include muscovite (KAl₂(AlSi₃O₁₀)(OH)₂) and biotite (K(Mg,Fe)₃(AlSi₃O₁₀)(OH)₂).

Muscovite and biotite are aluminum-containing silicates which cleave in thin sheets and are called micas. Muscovite has the general formula (KAl₂(AlSi₃O₁₀)(OH)₂) .

Muscovite has a pearly luster and can be clear in thin sheets. In small flakes, it gives sparkle to many rocks.

These samples of muscovite are on display at the Smithsonian Museum of Natural History. The sample at left is 20-30 cm high.

This sample of muscovite is from the Diamond mica mine in Keystone, South Dakota. There is also quartz content in the sample. The sample measures about 10 cm.

This sample of muscovite with quartz is about 10x18 cm and is from Panasqueira, Portugal.

Muscovite does not always clearly show the sheet structure in its overall appearance. This sample is about 16x18 cm and is from Hoydalen, Tordal, Kragero, Norway.

This thin sample shows the lighter color of muscovite in the center, surrounded by darker biotite. The sample is about 12x7 cm and is from Spruce Pine, North Carolina.