Question

How was coal formed? grade the varieties of coal in order of carbonisation.

Answer 1

Formation of coal:

• Coal is a fossil fuel which is formed when dead and decomposed organic matter (plants and animals) got buried due to natural calamities, such as volcanic eruptions, and earthquakes and was trapped inside the deeper layers of the earth.
• Coal takes millions of years to form.
• Under high temperature and pressure and less supply of oxygen, it was converted into coal which is a fossil.
• The slow process of conversion of wood into coal is called carbonisation.

Based on carbon content, coal is divided into four categories :

Peat :

• It is the first stage of the formation of coal.
• It contains 50-60% carbon.
• It is light brown in colour and is a cheaper form of coal.

Lignite :

• It is the second stage of the formation of coal.
• This variety of coal contains more than 60% carbon.
• It is brown in colour although harder than peat due to greater carbon content.

Bituminous:

• It is the third stage of the formation of coal.
• It contains 90%, 80% and 70% carbon depending upon whether it is high, medium or low quality.
• It is black in colour and hard.
• This variety of coal is most common and is known as household coal.
• It gives volatile and non-volatile substances on heating.

Anthracite :

• It is the last and fourth stage in the formation of coal.
• It contains 92-98% carbon.
• It is hard, black and dense.
• Although it is difficult to ignite but once ignited, it gives a lot of heat which lasts for a long time.