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Coal takes millions of years to form

Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is classified as a nonrenewable energy source because it takes millions of years to form. Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests.

The plants were covered by layers of dirt and rock over millions of years. The resulting pressure and heat turned the plants into a substance now known as coal.

Three images showing how coal was formed. The first image is of a swamp, 300 million years ago. Before the dinosaurs, many giant plants died in swamps.

The second image is of water, 100 million years ago. Over millions of years, these plants were buried under water and dirt.

The third image is of rocks and dirt over the coal. Heat and pressure turned the dead plants into coal.

Source: National Energy Education Development Project (public domain)

Types of coal

Coal is classified into four main types, or ranks: anthracite, bituminous, subbituminous, and lignite. The ranking depends on the types and amounts of carbon the coal contains and on the amount of heat energy the coal can produce. The rank of a coal deposit is determined by the amount of pressure and heat that acted on the plants over time.

Anthracite contains 86%–97% carbon, and generally has the highest heating value of all ranks of coal. Anthracite accounted for less than 1% of the coal mined in the United States in 2014. All of the anthracite mines in the United States are located in northeastern Pennsylvania. Anthracite is mainly used by the metals industry.

Bituminous coal contains 45%–86% carbon. Bituminous coal in the United States is between 100 and 300 million years old. Bituminous coal is the most abundant rank of coal found in the United States, and it accounted for 48% of total U.S. coal production in 2014. Bituminous coal is used to generate electricity, and it is an important fuel and raw material for making iron and steel. West Virginia, Kentucky, Pennsylvania, Illinois, and Indiana were the five main bituminous coal-producing states in 2014, accounting for 70% of total bituminous production.

Subbituminous coal typically contains 35%–45% carbon, and it has a lower heating value than bituminous coal. Most subbituminous coal in the United States is at least 100 million years old. About 44% of total U.S. coal production in 2014 was subbituminous, and nearly 90% was produced in Wyoming.

Lignite contains 25%–35% carbon and has the lowest energy content of all coal ranks. Lignite coal deposits tend to be relatively young and were not subjected to extreme heat or pressure. Lignite is crumbly and has high moisture content, which contributes to its low heating value. Lignite accounted for 8% of total U.S. coal production in 2014. About 92% of total lignite production is mined in Texas and North Dakota, where it is burned at power plants to generate electricity. A facility in North Dakota also converts lignite to synthetic natural gas and pipes it to natural gas consumers in the eastern United States.

Last updated: May 2, 2016

Coal statistics

Data for 2013 except where noted.

U.S. production
984.8 million short tons
U.S. consumption
925.1 million short tons
U.S. year-end coal stocks
197.5 million short tons
Average sales price
$37.24 per ton
Average delivered price
    Electric utilities
$45.12 per short ton
    Coke plants
$156.99 per short ton
    Other industrial plants
$69.167 per short ton
Largest producing state
Wyoming—387.9 million short tons
Share produced in Western region 54%
Share produced from surface mining 65%
Demonstrated reserve base 480 billion short tons (as of January 2014)
8.9 million short tons
117.7 million short tons
Electric power industry consumption
858.4 million short tons (93% of total U.S. coal consumption)
Coal share of electricity generation
Coal share of electric power industry generation capacity
Largest producing coal mine
North Antelope Rochelle Mine/Peabody Powder River Mining LLC.
111.0 million short tons
Leading producing company
Peabody Energy Corporation
183.3 million short tons
Average number of employees/miners
83,396 employees/miners
5.5 tons/miner-hour
1.8 tons/miner-hour
World coal production (2012)
8,694.8 million short tons
World coal consumption (2012)
8,449.5 million short tons

U.S. coal consumption by use
   Electric power sector
   Other industrial
   Coke plants
   Commercial and institutional
858.4 million short tons
43.3 million short tons
21.5 million short tons
1.9 million short tons

Top five consuming states of coal for electric power generation
102.5 million short tons
51.9 million short tons
46.7 million short tons
44.6 million short tons
41.4 million short tons

Last updated: April 1, 2016