Coal is a black or dark brown rock that burns and releases heat, formed from ancient plants that died millions of years ago, were buried under layers of earth, and were compressed over time. When you burn coal, it produces intense heat that can power steam engines, heat homes, or generate electricity.

For most of human history, coal was one of the most important sources of energy. The Industrial Revolution of the 1700s and 1800s ran on coal power: factories used it to run machines, trains burned it to pull heavy loads across continents, and ships carried it in their holds to power their engines. Cities grew around coal mines, and coal miners worked deep underground in dangerous conditions to extract this valuable fuel.

Coal mining shaped entire regions and ways of life. In places like Pennsylvania, West Virginia, and Yorkshire in England, coal mining created communities where generations of families worked in the same mines. The phrase back to the coal mines means returning to hard, grinding work.

Today, most countries are moving away from coal because burning it releases pollution and carbon dioxide that contributes to climate change. Many power plants now use natural gas, nuclear energy, or renewable sources like wind and solar instead. Still, coal remains important in some industries and countries.

You might also hear coal mentioned at Christmas: in old stories, naughty children supposedly received coal in their stockings instead of presents.