Download Sedimentary Rocks

Sedimentary Rocks - rocks formed from the hardening and cementing of layers
of sediment. Kinds of sedimentary rocks are clastic, chemical and organic.
The process of weathering produces sediment —loose particles of rock created by
the weathering and erosion of rock, by chemical precipitation from solution in
water, or from the secretions of organisms.
Sediment is transported and deposited by water, wind, or glaciers. Compaction
and cementation transform sediment into solid sedimentary rock. Lithification
refers to the processes by which sediments are transformed into solid sedimentary
rocks.
Clastic sediments are materials that originate and are transported as solid particles
derived from weathering. Clastic sedimentary rocks, which are classified by
particle size, contain a variety of mineral and rock fragments, with clay minerals
and quartz the chief constituents. Common clastic sedimentary rocks include shale
(the most common sedimentary rock), sandstone, conglomerate and breccia.
Chemical sediments are soluble materials produced largely by chemical
weathering that are precipitated by either inorganic or organic processes. Chemical
sedimentary rocks often contain the products of biological processes such as
shells or mineral crystals that form as water evaporates and minerals precipitate.
The most abundant chemical sedimentary rock is limestone, composed chiefly of
the mineral calcite. Rock gypsum and rock salt are chemical rocks that form as
water evaporates and triggers the deposition of chemical precipitates.
Organic sedimentary rocks are rocks that form from the remains of plants and
animals. Examples are: coal, limestone, coquina
Some of the features of sedimentary rocks that are often used in the interpretation
of Earth history and past environments include stratification, or beds (the single
most characteristic feature), bedding planes, fossils, ripple marks and mud
cracks.