Mica

mica

The mica group of sheet silicate, phyllosilicate minerals includes several closely related materials having nearly perfect basal cleavage.

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All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.

The name is derived from the Latin word mica, meaning a crumb, and probably influenced by micare, to glitter.

Occurrence

It is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals used for various applications are typically mined from granitic pegmatites.

Until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, their price dramatically dropped when large reserves were found and mined in Africa and South America during the early 19th century. The largest documented single crystal phlogopite was found in Lacey Mine, Ontario, Canada, it measured 10 m × 4.3 m × 4.3 m (33 ft × 14 ft × 14 ft) and weighed about 330 tonnes (320 long tons, 360 short tons). Similar-sized crystals were also found in Karelia, Russia.

The British Geological Survey reported that as of 2005, Koderma district in Jharkhand state in India had the largest deposits in the world. China was the top producer of mica with almost a third of the global share, closely followed by the US, South Korea and Canada. Large deposits of sheet mica were mined in New England from the 19th century to the 1970s. Large mines existed in Connecticut, New Hampshire, and Maine.

Production

Scrap and flake mica is produced all over the world. In 2010, the major producers were Russia (100,000 tonnes), Finland (68,000 t), United States (53,000 t), South Korea (50,000 t), France (20,000 t) and Canada (15,000 t). The total global production was 350,000 t, although no reliable data were available for China. Most sheet mica was produced in India (3,500 t) and Russia (1,500 t). Flake mica comes from several sources: the metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. The most important sources of sheet mica are pegmatite deposits. Sheet mica prices vary with grade and can range from less than $1 per kilogram for low-quality to more than $2,000 per kilogram for the highest quality.

Mica from Mogok, Myanmar

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