What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon rich, and harder material. The four ranks are:

  • Anthracite: The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter.
  • Bituminous: Bituminous coal is a middle rank coal between subbituminous and anthracite. Bituminous usually has a high heating (Btu) value and is the most common type of coal used in electricity generation in the United States. Bituminous coal appears shiny and smooth when you first see it, but look closer and you may see it has layers.
  • Subbituminous: Subbituminous coal is black in color and dull (not shiny), and has a higher heating value than lignite.
  • Lignite: Lignite coal, aka brown coal, is the lowest grade coal with the least concentration of carbon.

Also, there is peat. Peat is not actually coal, but rather the precursor to coal. Peat is a soft organic material consisting of partly decayed plant and, in some cases, deposited mineral matter. When peat is placed under high pressure and heat, it becomes coal.

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What is the biggest coal deposit in the United States?

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons of economic coal resources (also called reserves) in 2013.

Which country has the most coal?

The United States has the largest proven coal reserves, with an estimated 260.5 billion short tons of coal in 2008, according to the U.S. Energy Information Administration.

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. The coal is burned and the heat given off is used to convert water into steam, which drives a turbine. In 2012, about 39 percent of all electricity in the United States was generated by coal-fired power plants, according to the U.S. Energy Information Administration...

What is coal?

Coal is a sedimentary rock made predominantly of carbon that can be burned for fuel. Coal is readily combustible, black or brownish-black, and has a composition that, including inherent moisture, consists of more than 50 percent by weight and more than 70 percent by volume of carbonaceous material. It is formed from plant remains that have been...
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Date published: October 23, 2017

Assessments Evolved: USGS Coal Research in the 21st Century

Although often associated with helping fuel the Nation’s growth during the Industrial Revolution, coal is very much part of our space-age present. In 2016, coal-fired power plants provided 30.4 percent of the country’s electricity, and it is an important source of employment in many states.

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Image shows a sample of bituminous coal on a rock backdrop
December 31, 2013

Bituminous Coal

This sample is of bituminous coal, a middle rank coal (between subbituminous and anthracite) formed by additional pressure and heat on lignite. Usually has a high Btu value and may be referred to as "soft coal." Read more about USGS coal research here: https://energy.usgs.gov/Coal/

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Image shows a sample of cannel coal on a rock background
December 31, 2013

Cannel Coal

Cannel coal is a type of bituminous coal that is also sometimes referred to as a type of oil shale. It's name likely came from the word "candle." Cannel coal was once used as a source for kerosene. Read more about our coal research here: 

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Image shows a sample of clinker on a rock background
December 31, 2013

Clinker Coal

Clinker coal is the result of a seam of coal catching fire and burning so hot that it baked surrounding rock layers into brick-like formations. Some of the most famous clinker formations in the United States can be seen at the Theodore Roosevel National Park in North Dakota. Read more about our

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Image shows a sample of peacock coal against a rock background
December 31, 2013

Peacock Coal

This sample is of peacock coal. Peacock coal is not a specific class of coal, but rather the name for an effect in which oxidizing materials in the coal create a dazzling array of colors on the surface of the coal. Usually it is short-lived, as the material fully oxidizes away shortly after exposed to air. Read more about our coal research here: 

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Image shows a sample of lignite on a rock background
December 31, 2013

Lignite Coal

A sample of lignite, the lowest rank of coal. It is primarily mined for burning in steam-generation power plants. Read more about our coal research here: https://energy.usgs.gov/Coal/AssessmentsandData/CoalAssessments.aspx

Image shows a sample of anthracite coal on a rock backdrop
December 31, 2013

Anthracite Coal

This is anthracite, the highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter. Anthracite is not as commonly mined as other ranks of coal. It played a significant role in Pennsylvania coal during the Industrial Revolution in the United

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Image: Pliocene Lignite Coal from BEN Village

Pliocene Lignite Coal from BEN Village

Closeup of Pliocene lignite coal from a Balkan endemic nephropathy (BEN) village in Serbia. Lignite is low rank, or relatively unaltered (soft, or "brown") coal, and is characterized by a brownish color and appearance that often resembles wood. This lignite releases copious amounts of dissolved organic substances into groundwater.