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Pre-existing rocks or fragments of once-living animals are used to create sedimentary rocks. They are formed by the accumulation of sediments on the Earth’s surface. Layering and bedding in sedimentary rocks are common. Mesas and arches constructed of layered sedimentary rock can be seen in many of the scenic landscapes of the desert southwest.
Common Sedimentary Rocks:
Sandstone, limestone, and shale are examples of sedimentary rocks. These rocks are frequently formed from river sediments that are deposited in lakes and oceans. When sediments are buried, they lose water and get cemented, becoming rock. Tuffaceous sandstones contain volcanic ash.
Clastic Sedimentary Rocks:
When most people think of sedimentary rocks, they immediately think of clastic sedimentary rocks. Clastic sedimentary rocks are formed up of pre-existing rock fragments (clasts). Weathering loosens rock fragments, which are then moved to a basin or depression where sediment is trapped. Sedimentary rock is formed when sediment is buried deeply and crushed and cemented. Clastic sedimentary rocks can contain particles as small as tiny clay to as large as massive boulders. Their names are derived from the size of their clasts, or grains. Clay is the smallest particle, followed by silt, and finally sand. Pebbles are grains with a diameter of more than 2 millimetres.
Biologic Sedimentary Rocks:
When a significant number of living things die, biological sedimentary rocks form. This sort of rock is known as chert, and it is one of the ways limestone can originate. Limestone can also form as a result of water precipitation.
Examples of sedimentary rocks
- Caliche is found all over the world in dry or semiarid regions. It develops when mineral substances, mainly calcium carbonate, precipitates and hardens between rock fragments and sediment particles, cementing them together. Caliche can become extremely dense and robust over time, which is why it’s also known as hardpan, calcrete, and duricrust. It’s been dubbed a puddingstone by others.
- Chalk is a type of limestone made primarily of calcium carbonate and generated from the shells of foraminifera and the calcareous remains of coccoliths, which are small marine organisms. The colour of chalk is usually white or light grey. It has a porous, permeable, soft, and friable texture.
- Chert is a silicon dioxide-based microcrystalline or cryptocrystalline sedimentary rock (SiO2). It appears as nodules and concretionary masses, with layered deposits occurring less frequently. It fractures with a conchoidal fracture, resulting in razor-sharp edges. Early humans took advantage of the way chert breaks to create cutting tools and weapons. The specimen pictured above is approximately two inches (five centimetres) in diameter.
- Coal is an organic sedimentary rock formed by the collection and preservation of plant components, usually in a swamp. Coal, along with oil and natural gas, is a combustible rock that is one of the three most important fossil fuels. Coal is used for a variety of purposes, the most important of which being the creation of power.
- Conglomerate is a clastic sedimentary rock with big rounded particles (greater than two millimetres in diameter). Smaller particles and/or a chemical cement that ties the rock together cover the spaces between the stones. The specimen pictured above measures roughly two inches (five cm) in diameter.
Sedimentary rocks Uses
Sedimentary rock is used in almost all constructions and monuments. Below are some examples of how this type of rock can be used.
- Cement is made from limestone.
- Building stones are made of limestone and sandstone.
- Quartz is a sedimentary rock that is used in the production of glass.
- Plaster is made from rock gypsum.
- Sedimentary rocks are where natural gas, oil, coal, uranium, and other energy resources are created and extracted.
Conclusion
Most rocks have an unknown origin: they originate deep below the earth or in the past, before humans existed. Geologists use comparisons with what they can see to explain their genesis. They create a web of speculative evidence, relying on a convergence of lines of reasoning to arrive at conclusions that, over time, hold up to inspection with enough tenacity to be classified as ‘very probable.’
Ecologists, like many other scientists and professionals in a variety of professions, employ what is known as a “black box.” Each time a local issue is resolved, such as the origin of a specific invasive body, it adds to the corpus of settled disputes. When a significant number of identical situations have been settled in the same way after thorough examination, and when each case has reached the same conclusion, the issue is no longer deemed ‘problematic.’ The solution is evident, the problem is solved, and the explanation is accepted as a “fact.” The problem becomes a ‘non-issue,’ and it is relegated to a ‘black box,’ out of sight and out of memory. The focus of attention is elsewhere.
