Conglomerate 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 2 mm (0.079 in) 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.
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