Coal : Peat, Lignite, Bituminous coal, Anthracite and Graphite

Coal is a combustible black or brownish-black sedimentary rock, it is mostly carbon with variable amounts of other elements - hydrogen, sulfur, oxygen, and nitrogen.

Coal is formed when dead plant matter decays into peat and is converted into coal by the heat and pressure of deep burial over millions of years.

It is the largest anthropogenic source of carbon dioxide, 14.4 Gt in 2018, which is 40% of the total fossil fuel emissions and over 25% of total global greenhouse gas emissions.

China is the largest producer of coal, it mines almost half the world's coal, followed by India, US, Australia and Indonesia.

Due to high demand and poor average quality, India imports coking coal to meet the requirements of its steel plants. Dhanbad city is the largest coal producing city.

A large part of Indian coal is of low calorific value and high ash content. The carbon content is low and toxic trace element concentrations are negligible.

India has the fifth largest coal reserves in the world - primarily found in eastern and south-central India. Jharkhand, Odisha, Chhattisgarh, West Bengal, Madhya Pradesh, Telangana and Maharashtra accounted for 98.09 percent of the total known coal reserves in India.

The top five states in India with the largest coal reserves are - Jharkhand, Odisha, Chhattisgarh, West Bengal and Madhya Pradesh.

The top five states in India with the largest lignite reserves are - Tamil Nadu, Rajasthan, Gujarat, Pondicherry and Jammu and Kashmir.

Coal is the most abundant fossil fuel which holds 55% of India's energy need. Based on the uses, coal is divided into two types:

1) Coking Coal

Coking Coal when subjected to high temperature carbonisation i.e. heating in the absence of air to a temperature above 600 degree Celsius, forms a solid porous residue called coke.

Coke is fed into a blast furnace along with iron ore and limestone to produce steel in steel plants. Coking coal is desired to be of low ash percentage.

Coking Coal is mainly used in steel making and metallurgical industries and in hard coke manufacturing.

2) Non Coking Coal

Non Coking Coal does not have coking properties and is used in thermal power plants to generate electricity so it is also known as steam coal or thermal coal.

It is also used for for other heating purposes like: cement, fertilizer, glass, ceramic, paper, chemical and brick manufacturing etc.

Depending on the type and amounts of carbon the coal contains and on the amount of heat energy the coal can produce - Coal is also classified into four ranks: anthracite, bituminous, subbituminous, and lignite.


It is a soft black or brown natural substance that is formed from dead plants just under the surface of the ground in cool, wet places. It can be burned as a fuel or put on the garden to make plants grow better.

The formation of peat is the first step in the formation of coal. With increasing depth of burial and increasing temperature, peat deposits are gradually changed to lignite.

With increased time and higher temperatures, these low-rank coals are gradually converted to sub-bituminous and bituminous coal and under certain conditions to anthracite.


Lignite is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It is considered the lowest rank of coal due to its relatively low heat content. It has a carbon content around 25 to 35 percent.

It is mined all around the world and is used almost exclusively as a fuel for steam-electric power generation. Lignite is the most harmful coal to human health.

Jet, a compact form of lignite, sometimes polished - it is used as an ornamental stone.

Sub-bituminous coal

Sub-bituminous coal also called black lignite is a type of lower grade coal which contains 35-45 percent carbon. The properties of this type are between those of lignite, the lowest grade coal, and those of bituminous coal, the second highest grade of coal. It is primarily used as a fuel for steam-electric power generation.

Bituminous coal

Bituminous coal or black coal is a relatively soft, layered coal containing a tarlike substance called bitumen or asphalt. It is of higher quality than lignite and Sub-bituminous coal, but of poorer quality than anthracite.

The carbon content of bituminous coal is around 45?86 percent, the rest is composed of water, air, hydrogen, and sulfur.

It is used primarily as fuel in steam-electric power generation and to make coke.


Anthracite, also known as hard coal, is a hard, compact coal that has a submetallic luster. It has the highest carbon content, highest energy density and fewest impurities of all types of coal.

Anthracite is the most metamorphosed type of coal and it contains between 86-98 percent carbon.

Anthracite accounts for about 1 percent of global coal reserves. China accounts for the majority of global production; other producers are Russia, Ukraine, North Korea, South Africa, Vietnam, the UK, Australia, Canada and the US.


Graphite is a crystalline form of carbon with its atoms arranged in a hexagonal structure. It occurs naturally in this form and is the most stable form of carbon under standard conditions.

Under high pressures and temperatures it converts to diamond.

Graphite is difficult to ignite and not commonly used as fuel - it is most used in pencils, powdered for lubrication, electrodes, batteries, and solar panels.

Graphite is a good conductor of heat and electricity.