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Coal - National Geographic Society
Coal - Wikipedia
Coal | Uses, Types, Pollution, & Facts | Britannica
What is coal? | U.S. Geological Survey - USGS.gov
Coal explained - U.S. Energy Information Administration (EIA)
Coal: Anthracite, Bituminous, Coke, Pictures, Formation, Uses
Coal | Properties, Formation, Occurrence and Uses - Geology Science
Coal and the environment - U.S. Energy Information …
coal summary | Britannica
Coal - Carbon, Organic Matter, Sedimentary Rock | Britannica