Frequency Distribution of Clay Minerals in Major Great Soil Groups as Related to the Factors of Soil Formation

Abstract

The frequency distribution or relative abundance of minerals in soils varies with the five principal classes of factors that govern soil formation. The characteristics of the minerals of the parent material, the time factor, climatic factors, relief factors and biotic factors each can be shown to have important independent effects on clay mineralogy of soils under proper circumstances. The soil parent material exerts a control over the frequency distribution of minerals in soils by introduction of the clay minerals into the soil directly, by controlling the ecru'so of chemical weathering in the soil through the relative susceptibility of its minerals to weathering, by furnishing abundant divalent metallic cations, by impediment of drainage, or by acceleration of leaching when highly permeable. The time factor is conspicuous as long times give an advanced degree of weathering even in temperate climates. Climate is important, since highly weathered materials inevitably occur as a result of intense leaching in warm tropical and equatorial climates. Relief is important in concentrating leaching water and metallic cations, in affecting oxidation or reduction. The biotic factor affects minerals conspicuously where an A 0 horizon develops and resulting cheluviation moves R~Oa out of the A 2 horizon.Inherited minerals such as illite, quartz, feldspars, ferro-magnesian minerals, carbonates and gypsum are most abundant in Clays of little-weathered parent materials and soils of the zonal Desert, Brown, Chestnut and Tundra soils as well as intrazonal Mountain groups and azonal Regosols and Lithosols. Secondary layer silicate minerals such as vermiculite, secondary chlorite, montmorillonite, kaolinite and halloysite are

Formation of Halloysite from Feldspar: Low Temperature, Artificial Weathering Versus Natural Weathering

“…(1968) have shown electron micrographs of soil allophane exhibiting a certain degree of structural order that corresponds in form to the tapered projections formed on both artificially weathered feldspars. Perhaps, as suggested by Sudo and Takahashi (1956), Jackson (1959), andKeller (1964), during rock weathering minerals such as feldspar alter first to allophane and then to halloysite.4H20. The results of leaching experiments similar to this one (Pedro, and Berrier, 1966;Pickering, 1962) suggest that the flame-shaped sheets formed on the K-feldspar would have a chemical composition approximating allophane or halloysite.…”

“…"Field occurrences show that the clay mineral formed is commonly either allophane or halloysite..." He further noted that "In our present stage of knowledge, it may be stated that K-feldspar alters to kaolinite via intermediary mica under certain conditions, but directly to kaolinite under others, and that it alters to halloysite (endellite) via a gel phase, possibly including transitory allophane." Sudo and Takahashi (1956) suggested, and Jackson (1959) seems to agree, that there may be a gradual transition in the products of chemical rock weathering from allophane to halloysite 9 4HzO to halloysite. 2H._,O.…”

Formation and Stability of Hydroxy-Mg Interlayers in Phyllosilicates

“…Singleton (1965) reported the presence of hydroxy-Mg in addition to hydroxy-Al and -Fe in the interlayer space of clays from the Lookout series in Oregon. The formation of secondary chlorite in the dark magnesium clay soils of Hawaii and in Grumusols (Ladybrook Series) of Queensland, Australia, was related to the hydroxy-Mg interlayering in montmorillonite (Jackson, 1959 The presence of interlayered dioctahedral vermiculite, believed to contain at least some Mg-interlayer, and its relationships to the genesis of heat-stable chlorite were reported in Rappahannock estuary (Nelson, 1960), Neuse River of North Carolina (Brown and Ingram, 1954), and Chesapeake Bay area (Powers, 1954).…”

Formation of Dioctahedral Vermiculite in Virginia Soils

“…The interlayers also can be removed in the laboratory with citrate, fluoride, or other complexing agents. The weathering product, containing interlayers, has been described as a chlorite-vermiculite intergrade (Jackson, 1959). This name, although descriptive, does not indicate the extent of filling of the interlayer space, nor does it indicate the composition of the interlayer material.…”