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parent rock[′per·ənt ‚räk]
the upper layer of rock on which soil forms under the influence of biological and biochemical processes and human activity. The properties of the parent rock are changed in the process of soil formation through the effect of other soil formation factors such as climate and vegetation, but to a large extent the properties of the parent rock still determine the properties of the soils—mineralogical and chemical composition, texture (granulometric composition), physical properties, and fertility as a whole.
Parent rocks are distinguished according to origin (for example, alluvial and igneous), chemicomineralogical properties (carbonaceous, feldspar, quartz), and texture (sandy, loamy, clayey). Since parent rock greatly affects the soil characteristics, soil maps usually show parent rocks in addition to the genetic soil group (chernozems, podzols). The properties of the parent rock often determine the formation of different independent genetic groups of soils: types (for example, soddy-calcareous soils), genera (residually calcareous, residually solonetz), varieties based on texture, and classes based on the genesis of the parent rock.
V. M. FRIDLAND