Sedimentary rock: Introduction, formation, types, and Uses

What are the sedimentary rocks?

sedimentary rocks are the most common rocks found on the surface of the earth. However, the distribution of sedimentary rocks in the Earth’s crust is only 5%.

sedimentary rocks are formed by the weathering, transportation, and deposition of sediment, and lithification of sediment.

sedimentary rocks are important as they contain water, oil, natural gas. they also important because they giving us evidence of the earth’s history. Sedimentary rocks are the building blocks of various landform exist on the surface of the earth.

How sedimentary rock is formed?

The weathering, erosion, deposition of sediment, and lithification are the major process involved in the formation of sedimentary rock. Let’s look up the process of a sedimentary rock formation.

Weathering and sediments

Weathering is the process by which rock breakdown into smaller rocks or particles.

Preexisting rocks and minerals are often in contact with weathering agents such as water, wind, river, and ice. these weathering agents breakdown the rock into small rock particles. these small uncemented rock particles called sediment.

Transportation and deposition of sediment

 sediment is small and solid which is easily moved by erosive agents such as water, river, and wind. the process by which sediment transported to a new location called an erosion. the new location usually a low-lying area.

 the occurrence of landslide also transports the sediment to a new location. this process called mass wasting and it’s the most important occurrence of sediment transportation.

the transported sediment accumulates in its new location. this process of accumulation called deposition. This sediment is deposited in the bottom of ponds, seas, and lakes. sediment deposits in the form of layers, that are overlayed by new sediment by time.

Lithification: From sediment to solid rock

Accumulated sediments go through the lithification process. lithification is the process by which rock particles repack closely together and become solid.

What is lithification?

  The sediment contains a broken particle of the rocks and minerals. these rock particles become solid rock by lithification. The lithification process is completed in two stages.

              1. Compaction

              2. Cementation

1. Compaction

          when new sediment accumulates on the old sediment, the old sediment feels the high pressure due to burial. As a result of burial, sediment grains repack closely together and become compact sediment. this process called the compaction.

2. Cementation

  Cementation is the process where particles of the sediment are cemented by the cementing agents. These cementing agents fill the space between the particles. the calcite, quartz, clay, and hematite are the most common cementing agents.

By the process of compaction and cementation, the sediment become solid.

The process of compaction and cementation result in lithification. Thus, the lithification of sediment forms sedimentary rock.

Types of sedimentary rock

1. Clastic sedimentary rock

         Clastic sedimentary rocks are formed by the lithification of clastic sediment. clastic sediment is broken rocks and minerals particles that are solid and easily moved by the erosive agents. the broken particle is called a clast.

Clastic sedimentary rockclast or grain size   

Rounded, >2mm diameter

Angular and sharp clast, >2mm diameter
Sandstonesand-sized grains, 2 to 0.05 mm in size
Siltstonesilt-sized clast, 0.0039-0.0625 mm in size
shaleclay-sized particles and a minor amount of silt

Most of the sedimentary rocks are clastic type. The sedimentary rocks are named according to the sizes of the clast.

2. Chemical and biogenic sedimentary rock

 Chemical sedimentary rock formed of chemical sediment. Chemical sediment is formed when substances that have been dissolved are transported in solution and then deposited by precipitation.

Sometimes chemical sediment is formed by biochemical reactions in water, called biogenic sediment. The rock formed by biogenic sediment called a biogenic sedimentary rock.

Limestone, dolomite, cherts, and evaporites are the chemical or biogenic sedimentary rock.

3. Organic sedimentary rock

      This type of rock formed by the lithification of plants and animal remains such as leaves and roots.

Coal is an example of organic sedimentary rock. It is formed by the accumulation and lithification of plants that were buried in a swamp.

Economic use of sedimentary rocks

  • Limestone and sandstone are the build materials. They also contain natural gases, water, and petroleum.
  • Clay is used in pottery and bricks making.
  • Gypsum is used for plaster, wallboard, and also in making of plaster of Paris.
  • Gravel is used in road construction.

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