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Sedimentary Rock

Last updated date: 09th Apr 2024
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What are Sedimentary Rocks?

Sedimentary rocks alongside the metamorphic and igneous rocks are the three basic types of rocks that constitute Earth's surface. The sedimentary rocks often develop through layers and finally form on Earth's surface or close to the same. For weathering and Erosion, the agents are wind and rain – that forms these kinds of rocks. The precipitation and lithification processes involve the formation of sedimentary rocks by the emergence of new components, rocks and minerals. 

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Types of Sedimentary Rocks

The sedimentary rocks can be classified into three sorts – The Clastic sedimentary rocks – the types of stones that are formed from the remains and fragmentation of other rocks that existed earlier are the clastic sedimentary rocks. The chemical sedimentary rocks – these are the kind of rocks that develop from sediments that precipitate in a solution. The organic sedimentary rocks – These are the kinds of rocks that form from animal and plant remains or debris. 

Elaborating the Structure of Sedimentary Rocks

Sedimentary structures, observed under a microscope, show different sedimentary rocks, such as mud cracks, bedding, fossil trails and tracks, ripple marks, etcetera. Sedimentary structures can be broken into four kinds, depending on their time of genesis.

  • Primary Sedimentary Structures: The structures that develop alongside the development of the sedimentary rock that houses it.

  • Chemical Sedimentary Structures – these are the structures within a sedimentary rock that is formed from chemical processes. 

  • Secondary Sedimentary Structures: these are the structures in a sedimentary rock that develops from deposition and penecontemporaneous alterations.

  • Organic Sedimentary Structures: these are the structures formed from organic sources, that can be considered under any – primary, secondary or chemical structures are called the organic structures. 

Although sedimentary rocks' external structure in a sedimentary rock diagram may look just like concentric layers arranged one after the other, in actuality, the design is pretty complex. The recurring word while describing the structure of sedimentary rock is 'bedding'. 

What is Bedding  of Sedimentary Structures? 

It is the many layers of rock that constitute the mother rock. These beds are formed of different materials and are of varying sizes and shapes. It is characteristic of sedimentary rock to house beddings of varying sizes, from thin laminas to thick strata. Although the bedding in these rocks may appear in a range of arrangements, they are primarily found in horizontal configurations, signifying a tendency of deposition by the many agents – wind, air, water, etcetera flat-lying or horizontal layers. Imbricate bedding is the type of bedding formed out of tougher pebbles and stones that are flattened into layers. Other than these, some other structures include deformations during the many processes of sedimentary rock formations. 

Features of Sedimentary Rocks

Some of the traits that are commonly observed in sedimentary rocks are, 

  • Mud Cracks: Mud cracks are the fissures created when the water in sediments dry out. These cracks might get filled with water or other minerals sometimes. 

  • Bedding: The characteristic structure of a sedimentary rock that gives it a distinctive look is from the bedding or the layers of varying sizes that form the rocks.

  • Fossils: Sedimentary rocks often contain matters such as shells, bones and other remains from living organisms in their layers.

  • Distinctive Colour: The sedimentary rocks possess a distinct colour, that is, from the minerals involved in its creation or some external source during the same. Generally, the three primary colours seen in sedimentary rocks are white, black and red. 

  • Rain Prints: Often, the raindrops create impressions on the sedimentary rocks that might persist in the structure if preserved. 

  • Ripple Marks: the marks on the rocks that travel along water currents get ripple. These marks, thereby, are called ripple marks.

  • Cross-Bedding- whimsical and strong currents give rise to two beddings, a normal one and a shorter one, that exists in an intertwined pattern. These are called cross-bedding. 

  • Rill Marks: the types of slits created by waves that return to the ocean after hitting the shore are called rill marks.

FAQs on Sedimentary Rock

1. What are Some of the Most Common Sedimentary Rocks?


  1. Coals are a variety of organic sedimentary rocks and are formed from accumulated plant residue. Coal has been a source of fuel for a long time.

  2. Dolomite is a variety of limestone and falls under the category of chemical sedimentary rocks. 

  3. Limestone is one of the most commonly known sedimentary rocks. It can form organically, from the deposition of animal by-products and chemically by calcium carbonate precipitation.

  4. Sandstone is a variation of clastic sedimentary rocks that form from the accumulation of sand-sized debris in regions like deserts, deltas, etcetera.

  5. Iron ore is a chemically formed sedimentary rock reproduced when Iron and Oxygen combine in a solution, leaving behind sediments that finally become Iron ore.

  6. Shale is an example of clastic sedimentary rocks that are formed out of clay-sized debris.

Thereby, it is a complete layout of the formation, structure and examples of sedimentary rocks. 

2. How are Sedimentary Rocks Formed?

Answer: The formation of sedimentary rocks and the sedimentary rocks' structure involve diverse processes, to mention some – weathering, Erosion, precipitation, lithification, pressure from overbearing oceanic sediments, and, the decomposition of rocks and other living organisms leaves by-products in the form of sedimentary rocks.