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 the first attempts to use it as window glass. It appeared in Moscow 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 it was used to make products and glass panes. The origin of the name is connected with this: the word "muscovite" is derived from the words Moscow and Muscovy.

In addition to the name we use muscovite, the mineral was also called starfish, white mica, leukophyllite, antonite, sericolite, shernikite.

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

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 lay, they have different shades. Of the variety of shades, the most common are gray, milky white and white minerals. According to the degree of gloss, they stand out: pearlescent, silky or glassy muscovite.

Pieces of rock have a tabular, plucked or lamellar structure of a rhomboid cross-section. The edges are distinguished by horizontal shading, 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 (for the absolute of hardness, a diamond is taken, which has a hardness index of 10).

Moscovite is an elastic, resilient but fragile stone. It is easily split into separate plates, and has very good cleavage (a consequence of its crystal structure). It melts poorly (not lower than at 1600 ° C), while forming a yellow or gray nacre. At a temperature of 850 ° C, it loses water. When interacting with acid, it does not dissolve.

There are several ways to form muscovite,

1. Magmatic origin. Muscovite is found in vein rocks of igneous origin. And it never forms in erupted rocks. After cooling and crystallization of intermediate and felsic 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" rock) or collected in nests (they can reach 1.5-2 m). The layered structure indicates that it lies horizontally. Only the dissemination of large crystals is of industrial interest. Elements of such rocks as garnet, tourmaline, quartz, zircon, rutile and others are often found in their structure.
2. Metamorphic origin. At the contact of intrusions (geological accumulation of igneous rocks, formed deep in 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 the wind, small disseminations of muscovite in open areas are stratified and crumbled into small particles. If the weathering is of a chemical nature, then muscovite can pass into other formations.

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

• Fengit. A distinctive feature is a 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 mariposite.

• Damurite. It is white. It is a dense or finely scaly mineral. For disthena, it is the parent rock.

• Roscoelite. Fine-scaled mineral of green, brown or black color with a pearlescent sheen.

• Fuchsite. Stones with increased elasticity and refractoriness. Large crystals formed in chromium rocks. And as a result, the mineral contains an increased chromium content. They are bright green in color.

• Sericite. White mica with a fine-scaled structure and a silky sheen. It is found next to such types of mineralization as gold and copper. Formed in sericite schist, fellite, quartzite. It has a high silicon content. Does not interact with acid and hardly melts. Formed at medium and shallow depths under the influence of aqueous solutions and high pressure.

• Gumbelit. A mineral with a fibrous structure. It is gray in color. Extraction is carried out in the deposits of Karelia, together with coal shale.

• Gilbertite. A very rare form of mica. It has a fine-flaked structure. The color is green. It is mined in ore veins.

• Gilles Bertite. Muscovite, which is light yellow in color. 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 contain up to 30 types of impurities.

More than one trillion tons of mica are mined annually in the world. Russia, China and India topped the ranking of countries for the extraction of muscovite.

In the USA, production is carried out in the Sprut Pine field. And also a field is being developed in the state of North Carolina.

In Russia, muscovite is mined in the Mamsko-Chuisky, Stupinsky, and Yensky regions.

The Mamsko-Chuyskoye field is located in the Irkutsk Region in the Baikal-Patomskoye Upland. The explored rocks are 250 km long and 50 km wide.This is the largest mica deposit in Russia.

The Stupinsky region is located in Karelia, where such deposits as Plotina, Malinovaya Varakka, Tedino are being developed. And in the Yensky district of the Murmansk region, there are the Rubinovoye and Yena deposits.

Extraction of fine-scaled muscovite is associated with the extraction of rare metal ores. Such deposits are being developed in India (Rajasthan and Andhra Pradesh), Brazil, Canada and Zimbabwe. The fine-scaled muscovite from countries such as Pakistan and Finland is of a very high quality.

Muscovite of magmatic origin is mined from calcareous and crystalline shales in Italy (Piedmont Alps), the Russian Federation (Chelyabinsk region).

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

• Bihar (a state in the east of India, bordered by Nepal in the north). The territory located in the interior of the country. The deposit approaches the Himalayan mountain range. It accounts for 60% of the total production in the country.
• Andhra Pradesh (a state located on the southeast coast of the country). About 25% of the total production of sheet muscovite. Only muscovite and accompanying minerals are mined from this deposit. Ruby and green muscovite are mined.
• Rajasthan (a state in the northwest of India). About 15% of the total extraction of sheet muscovite.

Let's list the properties that this mineral possesses.

1. Color: white, silvery white, milky white, pinkish, light yellow, green, red, gray, greenish brown. Minerals containing multiple colors are sometimes found.
2. The mineral plates are transparent.
3. The fracture has a sheen of a pearlescent, silvery or silky shade.
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 hard 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. Melts at over 1500 ° C.
12. Nice temperature to the touch, 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 electrical industry.

There are several main uses for the mineral.

1. As a 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 stoves, mica glasses, insulators, capacitors or telephones.
2. Mica powder is used to create fire extinguishing media, fire-resistant ceilings, refractory paints and ceramics. In addition, it is used in the manufacture of mica cardboard, wallpaper, explosives, lubricants and others. The powder is made from scraps of sheet mica.
3. Creation of semi-finished products. For example, Mikanite. It is made from ground scraps of sheet mica, parts from muscovite, already in use and other mica waste. Mikanite production technology involves gluing individual pieces with shellac and pressing under high pressure.

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