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 coal usually has a high heating (Btu) value and is used in electricity generation and steel making in the United States. Bituminous coal is blocky and appears shiny and smooth when you first see it, but look closer and you might see it has thin, alternating, shiny and dull layers. 
  • Subbituminous: Subbituminous coal is black in color and is mainly dull (not shiny). Subbituminous coal has low-to-moderate heating values and is mainly used in electricity generation.
  • Lignite: Lignite coal, aka brown coal, is the lowest grade coal with the least concentration of carbon. Lignite has a low heating value and a high moisture content and is mainly used in electricity generation.

The precursor to coal is peat. Peat is a soft, organic material consisting of partly decayed plant and mineral matter. When peat is placed under high pressure and heat, it undergoes physical and chemical changes (coalification) to become coal.

 

COAL RANKS
Plant material --> Peat --> Lignite --> Subbituminous --> Bituminous --> Anthracite
----------------------> Increasing heat and pressure ---------------------->

 

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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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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: 

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Image shows a sample of bituminous coal on a rock backdrop
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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: 

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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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Clinker Coal

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Lignite Coal

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Anthracite Coal

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Coal mine in Power River Basin, Wyoming

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