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Caliche (''ka-lee'-chee'', or sometimes ''klee'-chee'') is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, including in central and western Australia, in the Kalahari Desert, in the High Plains of the western USA, in the Sonoran Desert, and in Eastern Saudi Arabia Al-Hasa. Caliche is also known as hardpan, calcrete, ''kankar'' (in India), or duricrust. The term ''caliche'' is Spanish and is originally from the Latin ''calx'', meaning lime. Caliche is generally light-colored, but can range from white to light pink to reddish-brown, depending on the impurities present. It generally occurs on or near the surface, but can be found in deeper subsoil deposits, as well. Layers vary from a few inches to feet thick, and multiple layers can exist in a single location. In northern Chile and Peru, ''caliche'' also refers to mineral deposits that include nitrate salts.〔p. 157, A Most Damnable Invention: Dynamite, Nitrates, and the Making of the Modern World, Stephen R. Bown, Macmillan, 2005, ISBN 0-312-32913-X.〕 Caliche can also refer to various claylike deposits in Mexico and Colombia. In addition, it has been used to describe some forms of quartzite, bauxite, kaolinite, laterite, chalcedony, opal, and soda niter. A similar material, composed of calcium sulfate rather than calcium carbonate, is called gypcrust. ==Formation== Caliche generally forms when minerals leach from the upper layer of the soil (the A horizon) and accumulate in the next layer (the B horizon), at depths of approximately three to 10 feet under the surface. It generally consists of carbonates in semiarid regions—in arid regions, less-soluble minerals form caliche layers after all the carbonates have been leached from the soil. The deposited calcium carbonate accumulates—first forming grains, then small clumps, then a discernible layer, and finally, a thicker, solid bed. As the caliche layer forms, the layer gradually becomes deeper, and eventually moves into the parent material, which lies under the upper soil horizons. However, caliche also forms in other ways. It can form when water rises through capillary action. In an arid region, rainwater sinks into the ground very quickly. Later, as the surface dries out, the water below the surface rises, carrying up dissolved minerals from lower layers. This water movement forms a caliche that tends to grow thinner and branch out as it nears the surface. Plants can contribute to the formation of caliche, as well. Plant roots take up water through transpiration, and leave behind the dissolved calcium carbonate, which precipitates to form caliche. It can also form on outcrops of porous rocks or in rock fissures where water is trapped and evaporates. In general, caliche deposition is a slow process, but if enough moisture is present in an otherwise arid site, it can accumulate fast enough to block a drain pipe. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Caliche」の詳細全文を読む スポンサード リンク
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