Sometimes this mineral, which got its name for some resemblance to snake skin (Latin serpens - "snake"), is mistakenly called a serpentine. Serpentine is a rock, and here we will talk about the mineral serpentine.
Composition and crystal structure
Serpentine is a group name for minerals that are similar in chemical composition and structure, belonging to the subclass of layered silicates. The general formula for serpentines is X3[Si2O5](OH) 4, where X is magnesium Mg, ferrous or trivalent iron Fe2+, Fe3+, 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 large variety of forms of excretion.
A brief description of serpentines
Minerals,belonging to the group of serpentines, there are quite a few (about twenty), but the main representatives of the group are three types:
- Antigorite is a sheety, scaly mineral that is easily separated. Sometimes it forms a solid mass. Has a pale green or greenish gray color.
- Lizardite is a green, greenish-blue, yellow, or white mineral that often forms glue-like, hidden-lamellar aggregates.
- Chrysotile - has a fine-fibered structure, light green, sometimes golden in color. A variation of it is chrysotile asbestos.
Serpophyre, or noble serpentine, is a mineral of a yellow-green hue, usually composed of lizardite or antigorite. It is characterized by dense aggregates, translucent at the edges.
Serpentine has other varieties with different contents of nickel, iron, manganese: nepuite, garnierite, amesite and so on. For example, the serpentine shown below in the photo is a nepuite mineral. It contains a lot of nickel (sometimes completely replacing magnesium) and can serve as an ore for this metal.
Physical and chemical properties of serpentine
The mineral has the following physical characteristics:
- density - from 2.2 to 2.9 g/cm3;
- Mohs hardness from 2.5 to 4;
- shine - glassy, with a greasy or waxy sheen;
- cleavage - none, except for antigorite (rare);
- line is white;
- kink - conchoidalcryptocrystalline aggregates, smooth in lamellar, splintery in asbestos (chrysotile).
Sulfuric and hydrochloric acids decompose serpentine. The mineral often contains various chemical impurities that affect the color.
Serpentine in 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 practically monomineral rocks formed during it are called serpentinites. They may have a small admixture of relic minerals such as olivine.
Also, dolomites (sedimentary carbonate rocks) exposed to hydrothermal fluids can transform into serpentine.
Serpentinites usually occur in the form of irregular arrays and lenticular bodies, widely distributed throughout the world. On the territory of Russia, the Urals, Karelia, the North Caucasus, Central and Southern Siberia, Transbaikalia, and the Kamchatka Territory are very rich in serpentinite deposits.
Decorative stone
Serpentinite, used as an ornamental and facing material, is often called a serpentine. This is how the stone was called by the Ural masters, who have been working with it for a long time. Due to the wide variety of textures and shades, as well as its sufficiently high strength and toughness, combined with low hardness, serpentine is a popular decorative stone.
Coils can be stacked with different types of serpentines. Minerals chrysotile and serpophyre (nobleserpentine) form a kind of serpentine, which is distinguished by the highest decorative qualities - ophiocalcite, or, in other words, serpentinite marble. It is a fine-grained rock, based on chrysotile and accompanying calcite, and serpophyre is present in the form of numerous inclusions and veinlets.
The serpentine has been used since ancient times: vases from it, created in pre-dynastic Egypt, are known. Statue of Pharaoh Amenemhat III circa 1800 BC. e., a fragment of which is kept in the Munich Museum, is also made of serpentinite. Currently, all kinds of souvenirs and interior decoration elements are made from serpentine (it is not used as an external facing material due to poor weather resistance).
Use of serpentines in industrial fields
In the technical industries, the use of serpentines is also quite widely developed.
The mineral chrysotile-asbestos, for example, is used in the manufacture of refractory fabrics and heat-insulating structures. In addition, it is valued as a material resistant to alkalis. The nepuite mentioned above and other nickel-containing serpentines are an ore for nickel. Some minerals of this group with a high content of magnesium can serve as an important raw material for the production of this metal in the chemical industry.
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 water and gas purification.
Massifs of serpentinized rocks are of interest from the point of view of prospecting and exploration of accompanying deposits of such valuable minerals as diamonds, platinum and chromite ores.
