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loose deposits that occur when the original (parent) rock weathers at its place of origin. The eluvium comprises weathering crusts and soils.
A distinction is made between the orthoeluvium of crystalline (magmatic and metamorphic) rocks, the metaeluvium of consolidated sedimentary rocks, and the neoeluvium of young, unconsolidated deposits (in the last two cases, the parent rocks consist largely of redeposited and slightly altered products of weathering). The most characteristic type is orthoeluvium, which ranges in composition from pebbles and boulders in cold climates to clays in hot, humid climates. On the basis of degree of decomposition, a distinction is made between siallitic eluvium, in which the original aluminosilicates are preserved; acidic siallitic eluvium, which is composed chiefly of newly formed hydrous aluminosilicates of the group of clay minerals; and allitic, or ferralitic, eluvium, in which a significant share of the silicates have decomposed and are represented by free hydroxides of aluminum and iron.
E. V. SHANTSER