Muscovite and biotite, commonly found in pegmatite rocks, are varieties of which mineral?

Muscovite and biotite are the two most common varieties of mica. They occur mainly in pegmatite, a very coarse-grained igneous rock formed from the last stages of cooling magma, in which crystals can grow very large.

About mica:

Mica is a group of silicate minerals that form thin, flat, flexible sheets. It splits easily into very thin, transparent or translucent layers, a property called perfect cleavage.

Muscovite (white mica or "ruby mica"): light-coloured or colourless, rich in potassium and aluminium. It is the most important commercial variety.

Biotite (black mica): dark brown to black, rich in iron and magnesium.

Phlogopite (amber mica): another variety, brownish.

Properties and uses:

• Mica is an excellent electrical insulator and is heat resistant, so it is used in electrical and electronic equipment, capacitors and heating elements.
• It is used in paints, cosmetics (to give a shimmering effect), plastics, rubber and drilling mud.

Mica in India:

India has been one of the world's leading producers of sheet mica.

The Koderma-Giridih-Hazaribagh belt of Jharkhand and the adjoining Gaya-Nawada belt of Bihar have historically been the most famous mica-producing areas. Koderma was once called the "Mica Capital of India".

Mica is also found in parts of Rajasthan.

Problems in mica mining:

• Much mica mining in Jharkhand and Bihar has been illegal and unregulated, after many official mines closed in the 1980s.
• Reports have highlighted child labour in the collection of mica scrap for the global cosmetics and electronics industries.
• What is pegmatite?

Pegmatite is a rock made of very large crystals of quartz, mica and other minerals, often found as veins or dykes. It is also an important source of rare minerals such as beryl, tourmaline and lithium minerals.

Why not the other options?

• ✗Quartz is a hard silica mineral, used in glass and electronics.
• ✗Gypsum is a soft mineral (calcium sulphate) used in cement and plaster of Paris.
• ✗Asbestos is a fibrous mineral once used for insulation, now banned in many countries because it causes lung disease.