Sometimes this mineral, which got its name for some resemblance to snake skin (lat. Serpens - “snake”), is mistakenly called a serpentine. The coil is a rock, and we will talk about the mineral serpentine.
Composition and crystal structure
Serpentine is the group name for minerals that are similar in chemical composition and structure, belonging to a subclass of layered silicates. The general formula of serpentines is X 3 [Si 2 O 5 ] (OH) 4 , where X is magnesium Mg, ferrous or trivalent iron Fe 2+ , Fe 3+ , nickel Ni, manganese Mn, aluminum Al, zinc Zn. The ratio of components may vary, but magnesium is almost always present in serpentines.
Minerals of this group are characterized by a molecular layered crystal lattice, they do not form single crystals. Varieties of serpentine are distinguished by a wide variety of excretory forms.
A brief description of serpentines
Minerals belonging to the group of serpentines, there are quite a lot (about twenty), but the main representatives of the group are three types:
- Antigorite is a leafy, scaly mineral that is easily divided. Sometimes forms a continuous mass. Has a pale green or greenish gray color.
- Lizardite is a mineral of green, greenish-blue, yellow or white color, often forming glue-like crypto-plate aggregates.
- Chrysotile - has a fine fiber structure, light green, sometimes golden color. A variety of it is chrysotile asbestos.
Serpofire, or noble serpentine, is a yellow-green mineral, usually composed of lizardite or antigorite. It is characterized by dense aggregates, translucent in the edges.
Serpentine has other varieties with different contents of nickel, iron, manganese: nepuit, garnierite, amesite and so on. For example, the serpentine shown in the photo below is a mineral that does not drink. It contains a lot of nickel (sometimes completely replacing magnesium) and can serve as ore for this metal.
Physico-chemical properties of serpentine
The mineral has the following physical characteristics:
- density - from 2.2 to 2.9 g / cm 3 ;
- hardness on the Mohs scale from 2.5 to 4;
- Shine - glass, with a greasy or wax tint;
- cleavage - absent, with the exception of antigorite (rarely);
- the line is white;
- kink - conchoidal in cryptocrystalline aggregates, flat in lamellar aggregates, splintery in asbestos (chrysotile).
Sulfuric and hydrochloric acids decompose serpentine. Mineral often contains various chemical impurities that affect the color.
Serpentine in the rocks
The mineral is formed as a result of low-temperature hydrothermal metamorphism of ultrabasic rocks containing olivine and pyroxenes (dunites, peridotites). This process is called serpentinization, and almost monomineral rocks formed during it are called serpentinites. They may have a small admixture of relict minerals such as olivine.
Dolomites (sedimentary carbonate rocks) exposed to hydrothermal fluids can also pass into serpentine.
Serpentinites usually occur in the form of irregular arrays and lenticular bodies, widespread throughout the world. On the territory of Russia, the Urals, Karelia, the North Caucasus, Middle and South Siberia, Transbaikalia, and the Kamchatka Territory are very rich in serpentinite deposits.
Decorative rock
Serpentinite, used as ornamental and facing material, is often called a serpentine. That’s how the Ural craftsmen, who have long worked with it, nicknamed the stone. Due to the wide variety of textures and shades, as well as a sufficiently high strength and viscosity, combined with low hardness, the coil is a popular decorative stone.
Coils can be folded by different types of serpentines. The minerals chrysotile and serpofire (noble serpentine) form a kind of serpentine that is distinguished by the highest decorative qualities - ophiocalcite, or, otherwise, serpentinite marble. This is a fine-grained rock, the basis of which is chrysotile and associated calcite, and sickle is present in the form of numerous inclusions and streaks.
The coil has been used since ancient times: vases from it are known, created back in pre-dynastic Egypt. Statue of Pharaoh Amenemkhet III approximately 1800 BC. e., a fragment of which is stored in the Museum of Munich, is also made of serpentinite. At present, various souvenirs and interior decoration elements are made from the coil (it is not used as an external facing material due to poor weather resistance).
Industrial use of serpentines
The use of serpentines is also quite widely developed in the technical branches.
The chrysotile asbestos mineral, for example, is used in the manufacture of refractory fabrics and heat-insulating structures. In addition, it is valued as alkali resistant material. The above-mentioned nepuit and other nickel-containing serpentines are nickel ore. Some minerals of this group with a high magnesium content can serve in the chemical industry as an important raw material for the production of this metal.
Serpentines with a high degree of hydration are used in the organization of biological protection of nuclear reactors as backfill, concrete aggregates. Minerals depleted in iron with a high content of magnesium and silicic acid are used as raw materials for adsorbents used in the purification of water and gases.
Arrays of serpentinized rocks are of interest from the point of view of prospecting and exploration of related deposits of such valuable minerals as diamonds, platinum and chromite ores.