Most sedimentary rocks are clastic sedimentary rocks, formed from cemented sediment
grains that are fragments of preexisting rocks. The rock fragments can be either identifiable pieces
of rock, such as pebbles of granite or shale, or individual mineral grains, such as sand-sized quartz
and feldspar crystals loosened from rocks by weathering and erosion. Clay minerals formed by
chemical weathering are also considered fragments of preexisting rocks. In most cases the sediment
has been eroded and transported before being deposited. During transportation the grains may
have been rounded and sorted. Table 6.1 shows the clastic rocks, such as conglomerate, sandstone,
and shale, and shows how these rocks vary in grain size.
Most sedimentary rocks are clastic sedimentary rocks, formed from cemented sediment
grains that are fragments of preexisting rocks. The rock fragments can be either identifiable pieces
of rock, such as pebbles of granite or shale, or individual mineral grains, such as sand-sized quartz
and feldspar crystals loosened from rocks by weathering and erosion. Clay minerals formed by
chemical weathering are also considered fragments of preexisting rocks. In most cases the sediment
has been eroded and transported before being deposited. During transportation the grains may
have been rounded and sorted. Table 6.1 shows the clastic rocks, such as conglomerate, sandstone,
and shale, and shows how these rocks vary in grain size.
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