Soil formation and soil type

Definition of Soil :

The term ‘soil’ is defined as an unconsolidated material,  composed of solid particles, produced by the disintegration  of rocks.

Soil Formation and Soil Types
On the basis of geological origin, soils may be organic or inorganic types.

Organic soils are extremely compressible and their use as a foundation material is avoided.

Peat, muck and humus are organic soils. Organic oil also known as cumulose soil.

Inorganic soils are formed by weathering of rocks due to mechanical disintegration or chemical decomposition.

Physical disintegration or mechanical weathering occurs due to the effects temperature changes, wedging action of ice, spreading of roots of plants and abrasion.

Due to physical disintegration, there is no change in chemical composition.

Coarse grained soils, such as gravel and sand are formed by the process of physical disintegration.

Chemical decomposition or chemical weathering of rocks occurs due to hydration, carbonation, Oxidation, solution and hydrolysis.

Due to chemical decomposition, original minerals are transformed into new minerals by chemical reactions.

Chemical decomposition of rocks results in formation of clay minerals.

Soils are obtained from geologic cycle, which goes on continuously in nature.

The geologic cycle consists of erosion, transportation, deposition and upheaval of soil.

Soils formed at the place of their origin are known as residual soil. Examples: Black cotton soils, laterite soils.

Soils deposited at a place away from the place of their origin, are called transported soil.

The soils formed at a place may be transported to other place by agents of transportation, such as water, wind, ice and gravity.



Commonly Used Soil Designation 

  1. Bentonite: Decomposed volcanic ash containing  a high percentage of clay mineral (i.e.,  montmorillonite). 
  2. Black cotton soil: It contains the mineral  montmorillonite mineral, and exhibits large swelling  and shrinkage. 
  3. Loam: It is a mixture of sand, silt and clay-size  particles approximately in equal proportions. 
  4. Moorum: It is gravel mixed with red clay. 
  5. Varved clay: It is clay and silt of glacial origin,  especially a lacustrine deposit.





Soil formation and soil type Soil formation and soil type Reviewed by Parag Pal on 12:00 AM Rating: 5

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