Classification

The coal of India may be classified under two categories: (i) Gondwana coal, and (ii) Tertiary coal. Gondwana Coal The Gondwana coal belongs to the carboniferous period (570 million years to 245 million years back). It is found in the Damodar , Mahanadi, Godavari, and Narmada valleys. Raniganj,Jharia, Bokaro, Ramgarh, Giridih, Chandrapur, Karanpura, Tatapani, Talcher, Himgiri, Korba, Penchghati, Sarguja, Kainpte, Wardha Valley, Singareni (A.P.) and Singrauli are some of the important coal mines of the Gondwana formations. Thejharguda coal mine (Madhya Pradesh) is the thickest coal seam 132 metres of the Gondwana Period, followed by the Kargali seam near Bokaro coalfield which is about 30 metres in thickness. Over 98 per cent of the total coal reserves of India belong to the Gondwana Period. The Gondwana coal is mainly bituminous or anthracite in which the carbon content varies between 60 to 90 per cent. The bituminous coal is converted into coke before being used in the iron and steel industry.

The Tertiary Tertiary coal is found in the rocks of the Oligocene period of the Tertiary Era. It is about 15 to 60 million years old. The Tertiary coal is also known as the ‘brown coal’. The Tertiary coal contributes only about two per cent of the total coal production of the country. It is an inferior type of coal in which the carbon varies between 30 per cent in Gujarat and Rajasthan to 50 per cent in Assam. Lignite coal is found in Arunachal Pradesh, Assam, Gujarat (Kachchh) Kerala, Jammu and Kashmir, Nagaland, Tamil Nadu, Uttar Pradesh, and West Bengal (Darjeeling District). The largest lignite deposits of the country

are at Neyveli in the state of Tamil Nadu. The different types of coal and their characteristics have been given in the following:

(i) Peat It contains the highest percentage of moisture, gives more smoke, has less than 40 per cent carbon and, therefore, is the lowest and most inferior quality of coal. It represents the first stage of coal formation.

(ii) Lignite (Brown-Coal) Lignite is superior to peat. Under the increasing pressure and heat, with the passage of time, peat is converted into lignite. It contains 40 to 60 per cent carbon. It is mainly found in Neyveli (Tamil Nadu), Palna (Rajasthan), Lakhimpur (Assam), Jaintia Hills (Meghalaya), Nagaland, Kerala, Jammu and Kashmir, Uttar Pradesh, and the union territory of Pondicherry. Lignite deposits in India have been estimated around 38930 million tonnes, out of which 4150 million tonnes are in Neyveli area of Tamil Nadu (2010). Lignite is also found in Assam, Gujarat, Jammu

& Kashmir, Kerala, Meghalaya, Nagaland, and Rajasthan.

(Ui) Bituminous (Black-Coal) When coal is buried very deep, the moisture gels expelled. The seam subjected to increased temperatures results into the formation of bituminous coal. It is dense, compact and black in colour. The traces of original vegetation from which it has been formed are found in this coal. Containing 60 to 80 per cent carbon, it is the most popular coal in commercial use. The name is derived after a liquid called bitumen released after heating. Bituminous coal is also used in making coke (coking coal), gas coal, and steam coal. Coking coal results from the heating of coal in the absence of oxygen, which burns off volatile gases and is mainly used in iron and steel industry. Most of the bituminous coal is found in Jharkhand, Odisha, Chhattisgarh, West Bengal and Madhya Pradesh.

(iv) Anthracite (Hard Coal) It is the highest quality of coal containing 80 to 90 per cent carbon. It has very little volatile matter and insignificant proportion of moisture. It has short blue flame. Of all the coals, it is the most expensive.