Coal occurs in the sedimentary rocks. It was formed when plants and ferns were buried in the swamp forests. Heat and pressure exerted by many layers which were formed over these decayed plants resulted in many physical and chemical changes.
Composition: Coal contains carbon, hydrogen, oxygen, nitrogen, and small amounts of phosphorus and sulphur.
Types of Coal
Depending on the amount of carbon, moisture, and volatile matter present, coal can be classified into four categories—anthracite, bituminous, lignite, and peat.
Anthracite
- It is the hardest and highest quality coal as it has a carbon content of over 90% and burns slowly without smoke.
- It leaves very little ash behind and has a high heating value.
Bituminous
- Its carbon content varies from 50% to 80%.
- It is hard and black. It makes up about 80% of the total coal output in the world.
- It is widely used for household purposes.
- It is popularly used in various industries. High grade bituminous coal is used in blast furnaces for smelting iron.
Lignite
- It is a low grade coal also known as brown coal.
- It is soft with high moisture content.
Peat
- It has the least carbon content and is inferior to the other three varieties of coal.
- It represents the first stage of transformation of wood into coal.
Uses of Coal
- It is used in thermal power plants for generating electricity.
- It is used as a source of heat and energy for domestic purposes.
- It is used for manufacturing iron and steel. It is used as raw material in many industries.
- Chemicals such as ammonia and benzol are obtained as by-products from the gases which are released when the coal is burnt in a closed chamber to get metallurgical coke.
Distribution of Coal in India
In India, coal is found in two main fields—Gondwana coalfields and tertiary coalfields. Bituminous coal is generally found in India.
Gondwana Coalfields
- It accounts for 98% of the total coal reserves in India. It is nearly free of moisture.
- It is found in the river valleys of Damodar, Mahanadi and Godavari.
- Gondwana coal deposits are found in West Bengal, Jharkhand, Odisha, Chhattisgarh, Madhya Pradesh, Uttar Pradesh and Andhra Pradesh.
Tertiary Coalfields
- It is found in the tertiary coalfields has high moisture content.
- These fields are generally found in Assam, Arunachal Pradesh, Meghalaya and Nagaland.
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