Mineralogy. Exogenic processes of minerogenesis.

In the superficial band of earth crust there is a thick process of fracture of minerals and rocks. Plurality of the phenomena of chemical and physical fracture carries the blanket name of airing.

Airing processes. Airing processes lead to mechanical fracture and chemical decomposition of soils and minerals.

Agents of airing are water and a wind, oscillations of temperature near to a surface, oxygen and air carbonic acid, ability to live of organisms. Intensity of airing also depends on a climate, a lay of land, an elemental composition of soils and minerals.

As a result of physical airing there is a mechanical fracture of soils and minerals - their disintegration. The detrital material or remains on a place, or is transferred by water streams. New minerals thus it is not formed, but as a result of mechanical fracture, transport and deposition scatterings - the important radiant of many valuable minerals are formed.

At chemical airing there is a chemical decomposition of minerals and new minerals, inconvertible in the superficial requirements are formed.

Airing processes in ore deposits have great value. In the lodes uncovered by erosion fundamental ore minerals, in particular sulphides, easily collapse and transfer in the secondary, oxidised minerals - sulphates, oxides, carbonates and other linkings.

Bands of acidification of sulphidic deposits, or "gossan" bands are as a result formed.

Main mineral of a band of acidification is limonite.

Below a ground-water level the cementation band, or secondary sulphidic dressing behind which there are fundamental not oxidised ores follows. In a band of cementation of water contain hydrogen sulphide and sulfuric acid; in them there is the free oxygen. Sulphates of metals react with fundamental ores therefore secondary ores are formed.

Sedimentary process. The huge masses of rocks destroyed as a result of airing and minerals move fluid waters. Thus there is a sorting of a material and its deposition. So the mechanical heels having very a wide circulation are formed.

Chemical sedimentation of minerals can occur both from true and from colloidal solutions. From supersaturated solutions of substance precipitated. Such is an origin of various salts: gypsum, a halite, carnallite, etc. It is the chemical heels.

The major role in fracture of minerals and rocks and in their new growth is played by live organisms, mainly various bacteria. Therefore it is possible to ooze biogene or biochemical process is more exact. Participation of organisms in formation of phosphorites, native sulphur, iron and manganese ores is erected. The minerals formed with the assistance of organisms have suggested to term as biolits. It is possible to carry to biolits and soils, for example, carbonate (chalkstones, a chalk) which were formed as a result of an accumulation of organisms with a limy skeleton, and also hard coal, peat, etc.

Metamorphic rocks. Sedimentary rocks thanks to earth crust motions can get to deeper bands of a lithosphere where there are other thermodynamic requirements, than on a surface. Thus they will test changes - a metamorphism which primary factors are the temperature and pressure. The mechanism metamorphic processes consists in dehydration, a recrystallization and the metasomatic phenomena. So, chalkstone, being exposed to a metamorphism, transfers in crystalline granular soil - marble, sandstone - in quartzite. Magmatic soils can be exposed to a metamorphism not only sedimentary, but also.

Ooze contact, a dislocation and regional metamorphism.

The contact metamorphism is shown on contact of two soils, usually magmatic and sedimentary. If the magmatic melting having temperature nearby 1000 ° and rich various gases, under major pressure is implanted in overlying soils, that, naturally, the last should react with it, especially, if it is chemically active soils, such, for example, as chalkstones.

The dislocation metamorphism is usually expressed in crushing and retyranny of rocks and in formation of tectonic breccias.

The regional metamorphism proceeds on major depths and grips the huge areas. At a regional metamorphism, for example as a result of a recrystallization at unilateral pressure, minerals which in other requirements do not arise can be formed.

To a regional metamorphism relate also formation of so-called dry fractures. These venous bodies developed in metamorphic soils, are formed thanks to tectonic stresses in disrupture places.

Typomorphic signs, oscillations and paragenesis of minerals. Signs on which with known approach it is possible to erect a composition, temperature of formation or an origin of minerals, carry names of the typomorphic.

Minerals are formed in the nature under certain physicochemical requirements of environment. Change of these requirements, for example a composition of environment, leads to a certain extent to change of a composition of minerals that is reflected in their colour.

The minerals possessing typomorphic signs, are termed as typomorphic minerals.

Each mineral is formed in a certain temperature interval. Sometimes this interval makes hundreds degrees, in other cases the temperature of formation more or is less spotted. It allows to grade minerogenesis processes conventionally. So, for example, low-temperature quartz is formed at temperature more low 575°С. Hence, and other minerals formed simultaneously with it or after him, also have education temperature more low 575°С.

On mutual relations of minerals among themselves, i.e. on cross of one minerals by others, in some cases it is possible to erect the order of their eduction. Quite often same mineral is oozed some times in the course of minerogenesis, i.e. has some oscillations.

Minerals of various oscillations quite often differ from each other on an elemental composition and exterior signs - to colour, quantity of grain, a facet etc. So, quartz of earlier oscillations often has grey colour, and later - white.

Paragenesis - joint formation of minerals in natural processes. Paragenetic associations of minerals are the groups of minerals formed thanks to the same process.