Sedimentary Rock

Sedimentary Rock : - in geology, rock composed of geologically reworked materials, formed by the accumulation and consolidation of mineral and particulate matter deposited by the action of water or, less frequently, wind or glacial ice. Most sedimentary rocks are characterized by parallel or discordant bedding that reflects variations in either the rate of deposition of the material or the nature of the matter that is deposited. Sedimentary rocks are classified according to their manner of origin into mechanical or chemical sedimentary rocks. Mechanical rocks, or fragmental rocks, are composed of mineral particles produced by the mechanical disintegration of other rocks and transported, without chemical deterioration, by flowing water. They are carried into larger bodies of water, where they are deposited in layers. Shale, sandstone, and conglomerate are common sedimentary rocks of mechanical origin. The materials making up chemical sedimentary rocks may consist of the remains of microscopic marine organisms precipitated on the ocean floor, as in the case of limestone. They may also have been dissolved in water circulating through the parent rock formation and then deposited in a sea or lake by precipitation from the solution. Halite, gypsum, and anhydrite are formed by the evaporation of salt solutions and the consequent precipitation of the salts.

sedimentary rock Rock formed by the accumulation and cementation of deposits that have been laid down by water, wind, ice, or gravity. Sedimentary rocks cover more than twothirds of the Earth's surface and comprise three major categories: clastic, chemically precipitated, and organic (or biogenic). Clastic sediments are the largest group and are composed of fragments of pre-existing rocks; they include clays, sands, and gravels. Chemical precipitates include some limestones and evaporated deposits such as gypsum and halite (rock salt). Coal, oil shale, and limestone made of fossil material are examples of organic sedimentary rocks. Most sedimentary rocks show distinct layering (stratification), caused by alterations in composition or by changes in rock type. These strata may become folded or fractured by the movement of the Earth's crust, a process known as deformation.