Sedimentary rocks

Sedimentary rocks are formed by the deposition and subsequent cementation on the material at the Earth’s surface within the bodies of water. These rocks are formed by four ways – deposition of weathered remains of other rocks, accumulation and the consolidation of sediments, deposition of the results of biogenic activity and lastly from precipitation from solution. Some common types of sedimentary rocks – limestone, chalk, clay, sandstone, and shale. These rocks cover 75% of the total earth’s surface.

Sedimentary rocks

Sedimentation is the combined name for all the processes that cause organic and mineral particles to get settle. The particle that helps in forming the sedimentary rock is called as sediment. This sediment is formed with the help of erosion and weathering from the source area and which is then transported to the deposition place by the wind, water, ice and glaciers which are agents of denudation.

The best way to examine the rock type is to check the sediment grain size and variation. Its texture refers to the features and arrangements of the grain in such sediments. Its structure is present in rock beds and under surfaces which help in recording the paleocurrents and has deposited in the rocks. It covers the continent of the earth’s crust, but the total contribution of these rocks is estimated to be by 8% of the total volume of the crust.

Types of Sedimentary Rocks

The sedimentary rocks are classified into three different forms – Organic, clastic and chemical sedimentary form.

Organic Sedimentary Rocks – This rock type mainly comprises of coal and limestones which is formed due to accumulation and deposition of dead plants and animals in rock layers.

Clastic Sedimentary rocks – This type of rock is formed when rock layers are formed due to the mechanical weathering of different rock types.

Chemical Sedimentary rocks –  This rock type is formed when there is a chemical reaction between minerals, present in rock forms cools down as precipitate and converts to rock form over a period of time.


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Two lenses with powers; 2D & -4D are kept together. What is the effective focal length of the combination?