A secondary or derivative rock composed of fragmented materials – for example, conglomerate, sandstone, shale, etc., which have been formed out of the remains of previously existing rocks. Besides the large class of sand-and-gravel rocks, clastic rocks also include many rocks of organic origin, such as certain limestones, composed of the debris of shells and corals; coals made of the remains of plants; and some ironstones consisting in whole or in part of organic debris. Fragmental volcanic rocks, such as tuff and agglomerate, come also into the same division.
Related category• GEOLOGY AND PLANETARY SCIENCE
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