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Coal - Wikipedia
Coal mining in the United States - Wikipedia
Coal - Simple English Wikipedia, the free encyclopedia
Coal mining - Wikipedia
Coal - National Geographic Society
Coal | Uses, Types, Pollution, & Facts | Britannica
Coal: Anthracite, Bituminous, Coke, Pictures, Formation, Uses
Coal explained - U.S. Energy Information Administration (EIA)
What is coal? | U.S. Geological Survey - USGS.gov
Coal - Carbon, Organic Matter, Sedimentary Rock | Britannica