Coals

Coals refers to a group of combustible sedimentary rocks formed from plant material that was buried and transformed under heat and pressure over geologic time. They occur in coal seams within sedimentary basins and are mined for energy and industrial uses. Coal ranks from least to most carbon-rich and energy-dense as peathood progresses: lignite (brown coal), sub-bituminous, bituminous, and anthracite. Peat is the precursor stage prior to coal formation. The term coals can also describe different deposits or shipments of coal.

Most coal is used for electricity generation in power plants, where it is burned to produce steam that drives turbines. A subset known as metallurgical or coking coal is used to produce coke for iron and steel manufacture in blast furnaces. Coal can also be processed into liquids or gases or used as a chemical feedstock in various industrial processes.

Mining and preparation methods vary. Surface (open-pit) mining removes overburden to reach coal seams, while underground mining includes room-and-pillar and longwall techniques. Before market, coal may undergo preparation to reduce ash and sulfur content and to improve handling and combustion characteristics.

Environmental considerations are significant. Combustion of coal releases carbon dioxide and other pollutants, contributing to climate change and air quality concerns. Mining and processing can affect land, water, and ecosystems, leading to regulatory standards and emissions controls. Reclamation and environmental rehabilitation are common post-mining practices.

Globally, coal reserves are large but unevenly distributed, with major producers including China, India, the United States, and Australia. Coal remains a major energy source in many regions, though its share is shifting in response to climate policy, economics, and the growth of alternative energy sources.