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The mica group of minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.
The word "mica" is thought to be derived from the Latin word micare, meaning to shine, in reference to the brilliant appearance of this mineral (especially when in small scales).

Mica is found abundantly throughout Asia, Africa, as well as North and South America. Until the 19th century, mica was quite rare and expensive as a result of the limited supply in Europe. However, its price dramatically dropped when large reserves were found and mined in Africa and South America after the early 19th century.

Mica has a high dielectric strength and excellent chemical stability, making it a favored material for manufacturing capacitors for radio frequency applications. It has also been used as an insulator in high voltage electrical equipment. It is also birefringent and is commonly used to make quarter and half wave plates. Because mica is resistant to heat it is used instead of glass in windows for stoves and kerosene heaters.

Specific varieties of mica include:

- Biotite
- Muscovite
- Lepidolite
- Phlogopite
- Illite

Mica in ancient times

The history of mica dates back to pre-historic times, and mica, the wonder mineral, was known to ancient Egyptian, Greek and Roman civilisations, and even in the Aztec civilization of the New World - for examples:

1) The earliest use of mica has been found in cave paintings created during the Upper Paleolithic period (40,000 BC to 10,000 BC), The first colors were red, iron oxide (hematite, a form of red ochre) and black (manganese dioxide), though black from juniper or pine carbons has also been discovered. White from kaolin or mica was used occasionally. The only other colors available to Magdalenian painters were yellow and brown. 3rd para, concluding part

2) A few kilometeres northeast of Mexico City stands the ancient site of Teotihuacan. The most striking visual and striking structure of Teotihuacan is the towering pyramid of the sun. One of the most amazing aspects pertaining to the pyramid of the sun was one-foot thick, sheet of granulated mica which had covered the entire top level of the Pyramid of the Sun. 4th para, opening part

3) Through out the ages, fine powders of mica have been used for various purposes, including decorative purposes. The coloured Gulal and Abeer used by Hindus of north India during holi festival contain fine small crystals of mica. The majestic Padmanabhapuram palace, Padmanabhapuram, 65 km from Trivandrum, India, has coloured mica windows.

Clay Micas

Illites, Muscovites and Biotites are all clay micas. They are all 2:1 clays, meaning they have two tetrahedral layers for every one octahedral layer. They have a low cation exchange capacity for 2:1 clays. K+ ions between layers of mica clays prevent swelling by blocking water molecules.

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