Rock-forming minerals are called minerals that are part of rocks as their permanent essential components. They differ from each other in their physical properties and chemical composition. In addition to rock-forming minerals, there are also minor ones. They occur in the form of impurities and do not play such a large geological role.
Plagioclase
Plagioclases are the most common rock-forming minerals. They are a mixture of anorthite and albite. There are many varieties of plagioclases. With an increase in the proportion of anorthite, the basicity of the mineral increases.
Plagioclases are unstable with respect to chemical weathering, due to which they become clay compounds. In this peculiarity, they are similar to feldspars. They can be used as facing and decorative material. Almost every rock-forming mineral of the plagioclase group is found in the Urals or Ukraine.
Nepheline
Nepheline belongs to the group of frame aluminosilicates. It is depleted in silica. Similar rock-forming minerals are part of igneous rocks, including nephelinites and nepheline syenites. They easily erode from the earth's surface and transform into kaolinite, as well as secondary formations of sulfate or carbonate composition.
Together with apatites, nepheline rocks can form vast massifs that are very important for modern industry. They are used in the production of glass, cement, alumina, silica gel, soda, ultramarine, etc. These main rock-forming minerals are found on the Kola Peninsula in the Murmansk Region.
Amphiboles and pyroxenes
Amphiboles, or tape silicates, include hornblende, which is an important rock-forming component in metamorphic and igneous rocks. Its distinguishing features are great strength and high viscosity. Most often, hornblende is found in the Urals.
Augite is a rock-forming mineral of pyroxenes. It is an essential component of igneous rocks. The color of augite can be very different (from black to green). This rock-forming mineral from the group of pyroxenes is part of basalt, andesite, diabase and some other rocks.
Mica
Some silicates have a layered, scaly, or leafy structure. The most common such minerals are asbestos, talc, kaolinite, hydromica, as well as mica (including muscovite and biotite).
What are their other features? Muscovite is a white mica found in metamorphic and igneous rocks. When weathering, it becomes loose. Muscovite is used as an insulating material. It is also used in construction, where mica powder is a common sprinkling material. Muscovite is mined in Eastern Siberia, the Urals and Ukraine.
Similar rock-forming minerals are biotites. This is magnesian and ferruginous mica of brown or black color. It is characteristic of metamorphic and igneous rocks. Biotite forms granular and scaly clusters. It is considered a chemically unstable mineral. Biotite is found in Transbaikalia and the Urals.
Hydromica
Another rock-forming rock mineral is hydromica. Their characteristic feature is a small number of cations. In addition, hydromica differ from mica by a significantly higher content in their composition of water, which is reflected in their name. Hydrothermal processes and weathering of rocks contribute to their formation.
The most valuable hydromica is vermiculite of brown or golden color. When heated, the molecular water of this mineral forms steam, expanding the interlayers in the crystal lattices, which increases its volume and density. Vermiculite is valuable due to its sound-absorbing and heat-insulating qualities.
Layered silicates
Minerals asbestos, talc, montmorillonite and kaolinite belong to the group of layered silicates. What is their feature? Talc formation occurs as a result of the interaction of hot solutions with aluminosilicates and magnesia silicates. It is used as a powder in the manufacture of plastics.
Like some other rock-forming minerals, asbestos is known as several of its varieties. It conducts electricity and heat poorly, is distinguished by alkali resistance and fire resistance. Chrysotile asbestos has the greatest value. It is formed from carbonate and olivine rocks. In long-fiber form, asbestos is used in the manufacture of some automotive parts and fireproof fabrics.
The most common clay mineral is kaolinite. It is formed as a result of weathering of mica and feldspars and is characterized by high stability. This mineral is white, grayish or brownish. Kaolin clay is used in the ceramic industry, where this raw material is used in the manufacture of faience and porcelain ceramics. Due to the properties of its forming mineral, these materials are ductile.
Montmorillonite is unusual in many ways. Its chemical composition is unstable and depends on the properties of the atmosphere, including the content of water in it. These main rock-forming minerals have a mobile crystal lattice, which is why they swell strongly when in contact with moisture.
Montmorillonite is formed in an alkaline environment due to the decomposition of tuffs and volcanic ash in water. It also appears in the places of weathering of igneous rocks and is resistant to chemical weathering. This mineral provides clayey rocks with additional adsorbability and swelling. Montmorillonite is used as an emulsifier, filler and bleach. Its deposits are located in the Crimea, Transcarpathia and the Caucasus.
Quartz
Mineral oxides are compounds of metals and oxygen. The most common representative of this group is quartz. This mineral is formed as a result of magmatic processes occurring in the deep earth's interior. It occurs in three variations: as cristobalite, tridymite and a-quartz. The last of these modifications is best studied.
Quartz is included in rock-forming minerals of igneous rocks (as well as sedimentary and metamorphic). It is chemically resistant. Quartz accumulates, forming thick sedimentary deposits, sands and sandstones. The mineral is used in the ceramic and glass industries. As a natural stone (sandstone and quartzite), it is popular as a structural and facing building material. It is also used in the manufacture of chemical glassware, optical instruments, etc.
Carbonates
Another group of rock-forming minerals is carbonates. They are widespread salts of carbonic acid. Carbonates are characteristic of metamorphic and sedimentary rocks. The most common types are magnesite, calcite and sodium. All of them have their own individual properties.
Calcite is characterized by low solubility in water. When exposed to carbon dioxide, it can go into bicarbonate. This product will dissolve in water a hundred times faster than regular calcite. This mineral is found in crystalline aggregates, sagging and thick deposits of marble and limestone. Calcite can form as a result of the accumulation of sludge. Another reason for its occurrence is the deposition of lime carbonate in water. Deposits are found in the Urals, Ukraine and Kaleria.
Magnesite is similar to calcite in shape and structure, but is much less common in nature. The reason is the factors of its formation. Magnesite is formed as a result of weathering of serpentinites, as well as the interaction of magnesian solutions and limestones.
Sodium nitrate is a white or colorless mineral found in the form of granular and dense masses. When heated, it dissolves. Sodium is formed in sodium salt lakes in the event of an excess of dissolved carbon dioxide in them. This mineral is used in metallurgy and in the manufacture of glass.
Opal
Opal is a widespread amorphous hydrated silica. It does not decompose in acids, but it is soluble in alkalis. There are several conditions for its formation. This mineral appears due to precipitation from geysers and hot solutions, as well as weathering of igneous rocks. In addition, it is formed due to the accumulation of waste products of organisms living in the sea. Opals are popular among jewelers.
Sulphates and Sulphides
Minerals sulfates are salts of sulfuric acid formed on the earth's surface. Most compounds of this group are not stable enough in the crust of the planet. Sulphates such as gypsum, mirabilite and barite are used for construction purposes. Anhydrite is a continuous granular mass. It is a crystalline mineral with a characteristic whitish-blue color.
When in contact with water, anhydrite increases volume and becomes gypsum, composing impressive rock formations. This sulfate is a typical chemical precipitate formed during the drying of the seas. Plaster and anhydrite are used as binders.
Heavy spar or barite is crystals with a specific tabular shape. It does not transmit X-rays well, which is why it is used in the production of special concrete. Barite is formed as a result of precipitation from aqueous hot solutions.
Sulfides are sulfur compounds with other elements. Cinnabar belongs to this class. This mineral is associated with young volcanoes. In nature, cinnabar is found in the form of veins and reservoir deposits. It accumulates in the form of placers due to its own stability on the earth's surface. Cinnabar is used in the synthesis of mercury and the manufacture of paints.