Weathering

Fizich. and chem. processes v. occur in the close interrelation with development and vital activity of animals and plants and action of the products of their disintegration after death. Most favorable for formation and retaining the products v. (minerals) on the spot are the conditions of tropich. or subtropich. of climate and it neznachit. the erosional breakdown of relief. With this thicker than the rocks, which were subjected v., is characteristic (in the direction from top to bottom) the geo-chem. zonality, expressed by the characteristic for each zone complex of minerals. The latter are formed as a result of the following after each other of the processes: the disintegration of species under the effect of fizich. V., the leaching of bases, hydration, hydrolysis and oxidation. These processes frequently continue to the complete decomposition of primary minerals, up to the formation of free oxides and hydroxides. Depending on the degree of acidity - the alkalinity of medium, participation of biogenic factors are formed the minerals of different chem. composition: from the steady in the alkaline medium (in lower the horizons) to the steady in the acid or neutral medium (into the top, the horizons). The variety of the products v., been different minerals, is defined by the classification of the minerals of primary rocks. For example, on the ultrabasic rocks (serpentinites) upper zone is the species, in the cracks of which are formed the carbonates (magnesite, dolomite), kerolith, sepiolite. The horizons further follow: carbonate formation (calcite, dolomite, aragonite), into the top, whose the parts on the cracks can be formed nickel kerolith, garnierite; the hydrolysis, with which is connected the formation of nontronite and the accumulation of nickel (NiO to 2,5%); silicification (quartz, opal, chalcedony). The zone of final hydrolysis and oxidation is folded by hydrogoethite (ocherous), by goethite, by magnetite, by oxides and by hydroxides of manganese (nickel and cobaltcontaining). With the processes v. of this type of species are connected the large layers of nickel, cobalt, magnesite and natural alloy zhel. of ores.

On carbonatites, which primarily consist it is more than to 90% of calcite, ankerite or siderite and small quantity of mineral- admixtures (pyroxene, amphiboles, tantalumniobates and rare-earth minerals), end products v. become friable. As a result of oxidizing the carbonates hydroxides of iron are accumulated, and oxides of calcium and magnesium undergo essential extension, which leads to an increase in the content of the mineral- admixtures, steady under the supergene conditions. In connection with this fresh carbonatites even with the negligible content of niobium, tantalum, rare earth and phosphorus with v. can give the industr. layers of these elements. With v. of coal (physical) occur its loosening before the formation of carbon soot, loss of luster, power change it is stratified; in the composition of coals with khim. V. the carbon content, hydrogen decreases, and oxygen in the organic mass it increases, furthermore, increases the humidity of coal, its capability for sintering is reduced, thermal conductivity decreases.

When products v. do not remain on the spot of their o^brazovaniya, but they are taken away from the surface of the being disintegrated species by water or by wind, frequently appear the unique forms of relief, which depend both on the nature v., and on the properties of the rocks, in which the process seemingly manifests and emphasizes the special features of their structure. For the igneous rocks (granites, diabases and others.) the massive rounded forms v. are characteristic; for the laminar sedimentary and the metamorphic - stepped (cornices, niche, etc.). The heterogeneity of species the unequal resistance of their different sections to v. conducts to the formation of outliers in the form of the isolated mountains, is column, towers and the like in the moist climate on the inclines of the uniform, comparatively easily water-soluble species, for example, limestones, the flowing waters corrode the irregular shapes of deepening, divided by jags and crests, as a result of which is formed the uneven surface, known under title. karrov. In the process of the regeneration of residual products v. are formed many soluble compounds, which are carried by ground water into the water basins and enter into the composition of the dissolved salts or they fall out into the sediment. Processes v. lead to the formation of different sedimentary rocks and many minerals: kaolins, ochers, the refractory clays, it is sand, the ores of iron, aluminum, manganese, nickel, cobalt, scatterings of gold, platinum, etc., zones of the oxidation of pyritic layers with their minerals, etc.

Lit.: Ginsburg i. i., the formation of the ancient crust of weathering to the territory OF THE USSR, its minerals and their properties, in the book; Transactions of the anniversary session, dedicated to 100- anniversary from the birthday v. V. dokuchayeva, M. - L., 1949; To and z and n s to and and Yu. p., weathering and its role in the steeling-accumulation, M., 1969; Weathering and lithogenesis, M., 1969.