Sedimentary Rocks

Sedimentary rocks form on the Earth’s surface by the deposition of material called sediments that include small pieces of organic matter, plants, minerals pieces belonging to once live organisms and pre existing rocks in the form of distinctive bedding or layering. This rock usually forms as layers at the bottom of Oceans and Lakes. It contains Siliciclastic (sedimentary non-carbonate clastic rocks) or quartz and calcite. Because sedimentary rocks usually consist of strata or layers, they are also called stratified rocks. This rock is generally arranged in clayey or sandy material called strata. Sedimentation is a collective name for the process which causes organic or mineral particles to accumulate and settle.

Types of Rocks

Sedimentary rocks are of three types

Clastic Sedimentary rocks- Fragments and pieces of rocks that ptrexisted form these types of rocks.. Weathering loosens these pieces of rocks.. This includes pieces of shells, stones and other objects. These pieces that are transported by wind and water settle down in different places where they are trapped as sediments. Clastic sediments are clay, sand, mud and silt. Mud and sand are mostly carried down the rivers to the Sea. Mud is made of clay, and sand is made of quartz. This rock is composed of rock fragments and silicate minerals. Examples of this rock include Breccias and Sand Stone.

Organic sedimentary rock- This type of rock rises in the sea as microscopic organisms. It forms when a large number of living organisms pile up, die and become compressed and thereafter, cemented forming rock. With a small scale of compaction, it becomes Peat. After much deeper and longer burial, it becomes Coal. Its deposits, mostly made animals’ shells and may form Chert, Coquina and Limestone. Coal and Peat are organic in both the Chemical and geological sense. This rock has high amount of organic material so it can be used as a source of tar and petroleum.

Chemical sedimentary rock-It is formed when mineral constituents in solution precipitate and supersaturate. This process starts when the sea water travelling through rock and minerals begins to come out of solution. Common chemical sedimentary rock includes evaporate mineral like Gypsum, Halite, iron ore, Balite and Sylvite and Oolitic limestone. Iron ore forms when oxygen and iron combine in solution and deposit as a sediment.


Sedimentary rock has economical importance because it contains the world’s entire store of natural gas, oil, phosphate, coal, ground water, other natural resources and salt deposits. It is also an important source of ores and fossil fuels. This rock is used in the construction of roads, buildings, canals and tunnels, rendering it very useful in civil engineering. Gravel, sand and cement are used to make concrete and iron ore for steel, bauxite used in making of aluminum, tile and brick. And the cut stone is used for facing large buildings. Limestone is an example of sedimentary rock and it’s composed largely of the mineral calcium carbonate. Limestone re crystallizes into marble during the mountain building process. Gypsum is used to make plaster of Paris in drywalls, and coal is used to generate energy. Smectite clay is also very useful as a digestive cure.

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