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Conglomerate is a coarse-grained clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts, e.g., granules, pebbles, cobbles, and boulders, larger than in diameter. Conglomerates form by the consolidation and lithification of gravel. Conglomerates typically contain finer grained sediment, e.g., either sand, silt, clay or combination of them, called ''matrix'' by geologists, filling their interstices and are often cemented by calcium carbonate, iron oxide, silica, or hardened clay. The size and composition of the gravel-size fraction of a conglomerate may or may not vary in composition, sorting, and size. In some conglomerates, the gravel-size class consist almost entirely of what were clay clasts at the time of deposition. Conglomerates can be found in sedimentary rock sequences of all ages but probably make up less than 1 percent by weight of all sedimentary rocks. In terms of origin and depositional mechanisms, they are closely related to sandstones and exhibit many of the same types of sedimentary structures, e.g., tabular and trough cross-bedding and graded bedding.〔Boggs, S. (2006) ''Principles of Sedimentology and Stratigraphy.'', 2nd ed. Printice Hall, New York. 662 pp. ISBN 0-13-154728-3〕〔Friedman, G.M. (2003) ''Classification of sediments and sedimentary rocks.'' In Gerard V. Middleton, ed., pp. 127-135, ''Encyclopedia of Sediments & Sedimentary Rocks, Encyclopedia of Earth Science Series.'' Kluwer Academic Publishers, Boston, Massachusetts. 821 pp. ISBN 978-1-4020-0872-6〕〔Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4〕 ==Classification== Conglomerates may be named and classified by the: * Amount and type of matrix present * Composition of gravel-size clasts they contain * Size range of gravel-size clasts present The classification method depends on the type and detail of research being conducted.〔〔〔Nichols, G. (2009) ''Sedimentology and Stratigraphy,'' 2nd ed. John Wiley & Sons Ltd, Chichester, West Sussex, United Kingdom. 419 pp. ISBN 978-1-4051-9379-5〕 A sedimentary rock composed largely of gravel is first named according to the roundness of the gravel. If the gravel clasts that comprise it is largely well-rounded to subrounded, it is a ''conglomerate.'' If the gravel clasts that comprise it are largely angular, it a breccia. Such breccias should called sedimentary breccias to differentiated them from other types, e.g., volcanic and fault, of breccias. Sedimentary rocks that contain a mixture of rounded and angular gravel clasts are sometimes called breccio-conglomerate.〔〔 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「Conglomerate (geology)」の詳細全文を読む スポンサード リンク
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