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    Author(s): C.D. Barton
    Date: 2002
    Source: In: Rattan Lal, comp., ed. Encyclopedia of Soil Science. New York, New York: Marcel Dekker: 187-192.
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (73 KB)


    Clay minerals refers to a group of hydrous aluminosilicates that predominate the clay-sized (<2 m) fraction of soils. These minerals are similar in chemical and structural composition to the primary minerals that originate from the Earth's crust; however, transformations in the geometric arrangement of atoms and ions within their structures occur due to weathering. Primary minerals form at elevated temperatures and pressures, and are usually derived from igneous or metamorphic rocks. Inside the Earth these minerals are relatively stable, but transformations may occur once exposed to the ambient conditions of the Earth's surface. Although some of the most resistant primary minerals (quartz, micas, and some feldspars) may persist in soils, other less resistant minerals (pyroxenes, amphiboles, and a host of accessory minerals) are prone to breakdown and weathering, thus forming secondary minerals. The resultant secondary minerals are the culmination of either alteration of the primary mineral structure (incongruent reaction) or neoformation through precipitation or recrystallization of dissolved constituents into a more stable structure (congruent reaction). These secondary minerals are often referred to as phyllosilicates because, as the name implies (Greek: phyllon, leaf), they exhibit a platy or flaky habit, while one of their fundamental structural units is an extended sheet of SiO tetrahedra.

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    Barton, C.D. 2002. Clay Minerals. In: Rattan Lal, comp., ed. Encyclopedia of Soil Science. New York, New York: Marcel Dekker: 187-192.

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