Iron minerals in soils on red-colored deposits

The presence of hematite in humus horizons of soils on red-colored deposits in the European part of Russia is related to the stability of this mineral and points to a low contribution of hematite iron to pedogenic hydroxidoge nesis. It is found that iron hydroxidogenesis develops in soddy-podzolic so ils on Permian deposits, brown forest soils, and typical chernozem. This pr ocess is not typical of the soddy weakly podzolic soil formed on the local moraine. Iron hydroxides in soils on red-colored deposits are represented b y acicular goethite, collomorphic hydrogoethite, ferroxyhyte, and protoferr ihydrite. In the soddy-podzolic soil, the thermodynamically stable goethite appears to be of chemogenic origin, other iron hydroxides being biogenic. In brown forest soils, the thermodynamically unstable iron hydroxides are f ormed under automorphic conditions, and the chemogenic synthesis of hydroxi des resulting in the formation of thermodynamically stable goethite (hydrog oethite) takes place under semihydromorhic conditions. Ferroxyhyte (especia lly Mn-ferroxyhyte) is more resistant to reductive solution and is, therefo re, more common in forest zone soils than ferrihydrite.