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Sedimentary Rocks


§        Sediment: means small pieces of rock

§        Formed by weathering, erosion and deposition.

o       Weathering: the breaking down of rocks and other materials on earth’s surface (caused by wind and water)

o       Erosion: The moving of materials caused by weathering

o       Deposition: The process where sediments that were carried by erosion are put in a new location. (Usually involves compacting and cementing of many materials together)

§        Sedimentary rocks are classified by the composition of the materials in them. 

§        There are three main categories:

o       Clastic Rocks: made from fragments of existing rocks and the size and shape of those pieces.  They are cemented together with clay, mud or sand.

§        Sandstone: made from sand-sized pieces

§        Shale: dust sized fragments (with mud or clay)

§        If over of the rock is made of pebbles, the rock is a conglomerate. Puddingstone is an example of a conglomerate.


o       Organic Rocks: made from organisms that were once living.

§        Organic means living

§        Many were formed from shells of crustaceans and microorganisms.

§        Limestone, and coral reefs are examples

§        Chalk is a type of fine-grained limestone.

§        Coal is another example


o       Chemical Rocks: formed when seas dried up, leaving minerals dissolve in the water.

§        Some Limestone forms this way.

§         Rock salt and Gypsum are other examples.