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Coquina () is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically-sorted fragments of the shells of molluscs, trilobites, brachiopods, or other invertebrates.〔U.S. Bureau of Mines Staff (1996) ''Dictionary of Mining, Mineral, & Related Terms.'' Report SP-96-1, U.S. Department of Interior, U.S. Bureau of Mines, Washington, D.C.〕〔Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4〕 The term ''coquina'' comes from the Spanish word for "cockle" and "shellfish".〔 " ' () shell-fish, cockle, deriv. of ''coca'' = ''フランス語:coque'':— *''ラテン語:cocca'', by-form of ''ラテン語:concha'' mussel, shell."〕 For a sediment to be considered to be a coquina, the particles composing it should average 2 mm or greater in size. Coquina can vary in hardness from poorly to moderately cemented. Incompletely consolidated and poorly cemented coquinas are considered grainstones in the Dunham classification system for carbonate sedimentary rocks.〔Dunham, R.J. (1962). ''Classification of carbonate rocks according to depositional texture''. In Ham, W. E.. Classification of carbonate rocks. American Association of Petroleum Geologists Memoir. no. 1, pp. 108-121.〕 A well-cemented coquina is classified as a biosparite according to the Folk classification of sedimentary rocks.〔Folk, R.L. (1980) ''The Petrology of Sedimentary Rocks.'' Austin, Texas, Hemphill Publishing Company. 182 pp. ISBN 0-914696-14-9〕 Coquinas accumulate in high-energy marine and lacustrine environments where currents and waves result in the vigorous winnowing, abrasion, fracturing, and sorting of the shells, which compose them. As a result, they typically exhibit well-developed bedding or cross-bedding, close packing, and good orientation of the shell fragments. The high-energy marine or lacustrine environments associated with coquinas include beaches, shallow submarine raised banks, swift tidal channels, and barrier bars.〔〔Scholle, P.A., D.G. Bebout, and C.H. Moore (1983) ''Carbonate Depositional Environments.'' Memoir no. 33. Tulsa, Oklahoma, American Association of Petroleum Geologists. 708 pp. ISBN 978-0-89181-310-1〕 ==Composition and distribution== Coquina is mainly composed of the mineral calcite, often including some phosphate, in the form of seashells or coral. Coquinas dating from the Devonian period through to the much more recent Pleistocene are a common find all over the world, with the depositional requirements to form a coquina being a common thing in many marine facies. 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「Coquina」の詳細全文を読む スポンサード リンク
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