Map of Coal Areas in North America

This map shows Coal Bearing Areas in the U.S.A., Canada, and Mexico. Coal Rank is filled with different shades of brown. The age of coal areas is depicted with different color strokes. For details, hover over the map. To take a closer look, zoom in. For more information, scroll down.

	Age
Lignite		Tertiary		Triassic-Jurassic
Lignite to Sub-bituminous		Triassic		Eocene
Sub-bituminous		Upper Cretaceous		Cretaceous
Bituminous		Lower		Jurassic
Anthracite		Mesozoic		Pennsylvanian
	Mississippian		Devonian

What is Coal?

Coal is a fossil fuel that is combusted to generate electricity. Along with oil and gas, it is a major nonrenewable fossil fuel.

Coal is the largest source of energy for electricity worldwide, and the most abundant fossil fuel in the United States.

Coal is black or brownish-black. By weight, it is 50% carbonaceous material. Coal also contains other elements like hydrogen, sulfur, nitrogen, and oxygen.

Coal is a sedimentary rock. Because it goes through physical and chemical changes due to increased heat it is sometimes misunderstood as a metamorphic rock. Many sedimentary rocks are also altered through burial-thermal processes. The University of Kentucky.

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Coal Formation

The formation of coal takes millions of years. The first coal-bearing rocks are 290-360 million years. This time is known as the Carboniferous or "coal-bearing" period.

During this time, Earth was covered in wide, shallow seas and dense forests.

There are also extensive deposits from the Cretaceous age, about 65 to 144 million years ago.

Coal began in swamps and wetlands where water stands slightly over the topsoil. In such locations, the vegetation produces organic matter quickly. Faster than it can be decomposed.

In these swamp layers, organic matter accumulated and is buried.

Coal Formation Process

Before we dwelve into coal's formation it is important to clarify that due to its origin, coal is not considered a mineral. This is because coal has a biological or organic source.

Minerals have to be from nonbiological (inorganic) sources. Minerals are also required to have of a crystalline form.

Coal formation process varies depending on the plants and conditions present. The whole process could be described in two phases, Peatification and Coalification.

Peatification

Coal formation process from peat to anthracite

Bacterial activity is the main process that creates peat.

Vegetation in wetlands, from ferns, shrubs, trees, and algae dies. It accumulates on the surface. This organic matter is decomposed by bacteria, producing carbon dioxide and methane.
Once the plant matter gets buried, it is no longer exposed to air. Anaerobic bacteria begin decomposing this material.
Burial and accumulation may occur for several thousands of years. It will produce several meters of partially decayed plant matter known as peat.

Coalification

Increasing temperature and pressure from burial are the main factors in coalification.

Once the peat is buried, water and other compounds are squeezed out. This is due to the increasing pressure. At this point, the lowest quality of coal, lignite, begins to form.
Consecutive burial results in increasing pressure and temperature. The lignite is transformed into higher-quality "black coal".
Lignite becomes sub-bituminous coal, then bituminous coal, and finally the highest-quality anthracite coal.
As coal transforms, water and other compounds decrease. The coal becomes dense and carbon concentration increases. Source: Energy Education.

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Coal Rank

Coal is altered through biological and burial-thermal processes into different ranks. Coal is ranked according to how much it has changed over time.

Hilt's Law states that the deeper the coal seam, the higher its rank. At deeper depths, the material encounters greater temperatures and pressure, and more plant debris is transformed into coal.

Type		Calorific Value (KJ/Kg)	Volatile Matter (%)	Carbon Content (%)
Peat		16,800	>53	20 to 30
Low-rank Coal (Brown Coal)	Lignite	23,000	53 - 49	25 - 35
Low-rank Coal (Brown Coal)	Sub-bituminous	29,300	49 - 42	35 - 45
Medium-rank coal (Black Coal)	Bituminous	36,250	42 - 29	45 - 86
High-rank coal (Black Coal)	Anthracitic	>36,250	29 - 8	up to 97

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Peat

Peat is not coal but it will eventually turn into coal.

Peat contains energy. It also has high amounts of volatile matter.

Peat has enough moisture to be spongy and absorb water. This makes it a valuable defense against flooding.

Lignite

This is the lowest rank of coal. It has low amounts of energy compared with other coals.

Lignite is about 250 million years old. It is brown, also called brown coal or rosebud coal.

It retains more moisture than other coals and it is crumbly. Because of this, it is more dangerous and expensive to mine and transport.

Lignite is susceptible to accidental combustion and has very high carbon emissions when burned.

Most lignite coal is used in power stations very close to where it is mined.

Lignite deposits are used to generate electricity in the states of North Dakota and Texas.

As seen on the map, Lignite bearing areas are found in Texas, Louisiana, Mississippi, Alabama, North Dakota, and Alberta.

Sub-bituminous Coal

Sub-bituminous coal is about 100 million years old. This type of coal is considered brown and used to generate electricity.

Sub-bituminous coal is found in Montana and Wyoming. It is mined in Wyoming and makes up 47% of the coal mined in the U.S.A.

Sub-bituminous coal is found in large quantities in thick beds near the surface. This brings its mining costs down.

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Bituminous Coal

Bituminous Coal is between 100 million to 300 million years old.

It is named after the sticky, tar-like substance called bitumen which is also found in petroleum.

Bituminous coal is blocky and appears shiny and smooth. If you look closer, you might see it has thin, alternating, shiny, and dull layers. They are the result of the different plant materials it is made up of. USGS.

Bituminous coal is used for about half the energy used in the U.S.A.

It is mined in Kentucky, Pennsylvania, and West Virginia. It is found in Michigan, Ohio, Illinois, Missouri, Utah, Colorado, and other states as seen on the map.

Anthracite

Most Anthracite occurs between 299 - to 359.2 million-year-old strata of the Carboniferous Period.

Anthracite is the highest rank of coal, with the most energy stored. It is harder, more dense, and more lustrous (shiny) than other coals.

It is so compact that it has almost no water or carbon dioxide.

The quality of this coal is so high, it burns with very little soot. Therefore, it is mainly used in stoves and furnaces. Anthracite is also used in water filtration systems. This is because it has tiny pores that can trap particles in the water.

Anthracite is found in Pennsylvania and Virginia. These areas have gone through a particular type of stressful geologic activity. Source: Natgeo.

Anthracite is rare in the U.S., as seen on the map. It accounts for 0.2% of total coal Production.

Coal Production in the U.S.A.

Not all states have coal-bearing areas, and not all coal reserves are recoverable. This depends on factors like competing land uses, profit margins, property rights, and physical or environmental restrictions.

Because of this, some states mine coal or have a history of mining coal while others do not. Source: American Geosciences.

According to EIA.gov, the top-producing states in 2021 are: