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conglomerate
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Old Red Sandstone conglomerates A chart categorizes common textural terms for rocks by grain size in millimeters, dividing them into igneous and metamorphic, sedimentary, and pyroclastic types, with terms like phaneritic, sand, silt, breccia, and ash shown in relation to size.
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Old Red Sandstone conglomerates
Old Red Sandstone conglomerates Old Red Sandstone conglomerates, Devonian age, from the Ardennes, Belgium.

conglomerate

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conglomerate, in petrology, lithified sedimentary rock consisting of rounded fragments greater than 2 millimetres (0.08 inch) in diameter. It is commonly contrasted with breccia, which consists of angular fragments. Conglomerates are usually subdivided according to the average size of their constituent materials into pebble (fine), cobble (medium), and boulder (coarse). A brief treatment of conglomerates follows. For full treatment, see sedimentary rock: Conglomerates and breccias. Classification of conglomerates is based on the range of lithologies...

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