Muscovite: features, types and properties

Mica has been known in Russia since the X-XII centuries. Its distribution began from Novgorod and the Karelian Peninsula. There were first attempts to use it as a window pane. In Moscow, she appeared only after the conquest of Novgorod by Ivan the Terrible. In the XVII-XVIII centuries. a large amount of the mineral was exported to Europe, where products and window panes were made from it. The origin of the name is also connected with this: the word “muscovite” is derived from the words Moscow and Muscovy.

In addition to the name used by us, muscovite, the mineral was also called starfish, white mica, leukophyllite, antonite, sericolite, shernikite.

Muscovite belongs to the group of mica, a class of aqueous aluminosilicates. The chemical formula is KAl2 [AlSi3O10] (OH, F) 2. Does not apply to jewelry materials. The main field of application is electronics.

It has the following composition:

• silicon - 45.3%;
• water - 4.2%;
• aluminum - 38.7%;
• potassium oxide - 11.8%.

These are white or colorless crystals. And depending on where they lie, they have different shades. Of all the variety of shades, gray, milky white and white minerals are most often found. According to the degree of brilliance, they are distinguished: pearlescent, silky or glass muscovite.

Pieces of rock have a tabular, plucked or lamellar structure of a rhomboid section. The faces are distinguished by horizontal hatching, and crystals with unique, uneven patterns of different shades.

The hardness of the mineral varies in the region of 2-2.5 on the Mohs scale (diamond, which has a hardness index of 10) is taken as the absolute hardness.

Muscovite is an elastic, resilient, but fragile stone. It easily splits into separate plates, and has a very good cleavage (a consequence of its crystalline structure). It melts poorly (no lower than at 1600 ° C), while forming a mother-of-pearl yellow or gray. At a temperature of 850 ° C, it loses water. When interacting with acid does not dissolve.

There are several ways to form muscovite,

1. Magmatic origin. Muscovite is found in veins of igneous origin. And never formed in the outflowing rocks. After cooling and crystallization of medium and acidic magmas, muscovite is released. It is a rock-forming part of some rocks (for example, granite). In this case, muscovite can be scattered over the entire area of ​​pegmatite (the area of ​​formation of the "main" breed) or collected in nests (they can reach 1.5-2 m.). The layered structure indicates that it lies horizontally. Of industrial interest is only the interspersing of large crystals. Elements of such rocks as garnet, tourmaline, quartz, zircon, rutile and others are often found in their structure.
2. Metamorphic origin. Upon contact of intrusions (geological accumulation of igneous rocks formed in the depths of the earth's crust) and rocks.
3. In layered clays and silty sediments. They get there as a result of the weathering process. Under the influence of wind, small inclusions of muscovite in open areas are stratified and showered with small particles. If weathering is of a chemical nature, then muscovite can pass into other formations.

Depending on where the minerals lie and what properties they possess, several types are distinguished.

• Fengit. A distinctive feature is its high silicon content. Magnesium and iron in the composition can replace aluminum. If an increased chromium content is noted in the chemical structure, then such a mineral is called mariposit.

• Damurit. It has a white color. It is a dense or finely scaled mineral. For distene, it is the mother breed.

• Roscoelite. Fine-grained mineral of green, brown or black color with a pearly tint.

• Fuchsit. Stones with increased elasticity and refractoriness. Large crystals formed in chromium rocks. And as a result, the composition of the mineral is high in chromium. They have a bright green color.

• Sericitis. White mica with a finely scaly structure and silky sheen. It is found next to such types of mineralization as gold and copper. Formed in sericite schist, fellites, quartzites. It has a high content of silicon. It does not interact with acid and hardly melts. Formed at medium and shallow depths under the influence of aqueous solutions and high pressure.

• Gumbelitis. A mineral with a fibrous structure. It has a gray color. Extraction is carried out in the fields of Karelia, together with carbonaceous shale.

• Gilbertite. Very rare form of mica. It has a finely scaly structure. The color is green. It is mined in ore veins.

• Gilles-berthit. Muscovite, having a light yellow color. It is formed at medium depths in pegmatite veins - large deposits that can reach 5-6 km in length.

• Illit (term). A mineral in which mica is mixed with clay. The structure remains lamellar.

The chemical composition of muscovite can have up to 30 types of impurities.

More than one trillion tons of mica is mined annually in the world. Russia, China and India topped the rating of countries for the production of muscovite.

In the United States, mining is underway in the Octopus Pine field. It is also developing a field in North Carolina.

In Russia, the development of muscovite is in the areas of Mamsko-Chuisky, Stupinsky, Jensky.

The Mamsko-Chuiskoye field is located in the Irkutsk Region on the Baikal-Patom Highlands. The length of the explored rocks is 250 km, and the width is 50 km.This is the largest mica deposit in Russia.

Stupinsky district is located in Karelia, there are developing such deposits as Plotina, Raspberry Varaka, Tedino. And in the Jensky district of the Murmansk region there are deposits of Rubinovoye and Ena.

The extraction of small-scaled muscovite is concomitant with the extraction of rare-metal ores. The development of such deposits is carried out in India (Rajasthan and Andhra Pradesh), Brazil, Canada and Zimbabwe. The finely muscovite mined in countries such as Pakistan and Finland is of very high quality.

Muscovite of magmatic origin is extracted from calcareous and crystalline schists in Italy (Piedmont Alps), the Russian Federation (Chelyabinsk Region).

The largest percentage of sheet muscovite mining is in India. Several areas with ore deposits have been developed there.

• Bihar (state in the east of India, from the north it borders with Nepal). Territory located inland. The field approaches the mountain range of the Himalayas. It accounts for 60% of the total production in the country.
• Andhra Pradesh (a state that is located on the southeast coast of the country). About 25% of the total production of sheet muscovite. Only muscovite and its associated minerals are mined at this deposit. Muscovite is extracted in ruby ​​and green colors.
• Rajasthan (state in northwest India). About 15% of the total production of sheet muscovite.

We list the properties that this mineral possesses.

1. Color: white, silver-white, milky white, pinkish, light yellow, green, red, gray, greenish brown. Minerals containing several colors are sometimes found.
2. Mineral plates are transparent.
3. The fracture has a tint of pearlescent, silver or silky color.
4. Refractive indices: Np = 1,552–1,572 and Ng = 1,588–1,615.
5. Mineral plates are elastic.
6. Hardness within 2-3 units on the Mohs scale (can be scratched with a solid object).
7. Density varies from 2.5 to 3.2 (depending on the percentage of iron content).
8. The surface relief is stepped.
9. Good dielectric.
10. Does not interact with acids.
11. It melts at temperatures above 1500 ° C.
12. To the touch of a pleasant temperature, non-greasy.
13. Weak resistance to weathering.
14. Associated minerals: tourmaline, apatite, quartz, garnet, staurolite.

The main areas of application of muscovite are instrumentation, radio engineering and the electrical industry.

There are several basic uses for the mineral.

1. As dielectric (muscovite has good electrical insulating qualities). For this, sheet mica is used. Depending on the size of the plates, their color and impurities in the mineral, they are used to create electric lamps, kerosene, mica glasses, insulators, capacitors or telephones.
2. Mica powder is used to create fire extinguishing agents, fire-resistant ceilings, refractory paints and ceramic products. In addition, it is used in the manufacture of mica cardboard, wallpaper, explosives, lubricants and more. Powder is made from scraps of sheet mica.
3. Creation of semi-finished products. For example, micanite. It is made from ground scraps of sheet mica, parts from muscovite, already used and other mica waste. Micanite production technology involves bonding individual pieces with shellac and pressing under high pressure.

You can see the beauty of the ruby ​​in Muscovite in the next video.