coal

Coal is a combustible sedimentary rock formed from the accumulated remains of plants that lived and died in swamps and bogs, subjected to heat and pressure over millions of years. It is primarily composed of carbon, along with varying amounts of moisture, ash, sulfur, and volatile compounds. As a fossil fuel, coal is mined from underground or surface deposits and used as a source of energy and carbon for industrial processes.

Coal exists in several ranks that reflect its degree of coalification and energy density: lignite, sub-bituminous, bituminous, and anthracite. Lignite has the lowest carbon content and heat value, while anthracite has the highest. Sub-bituminous and bituminous coals are widely used for electricity generation and metallurgy. The ranking correlates with moisture content and sulfur content, influencing suitability for different applications.

Extraction methods include surface mining (open-pit or strip mining) for near-surface deposits and underground mining for deeper seams. Mining can pose environmental and health risks, including landscape disruption, water pollution from acid mine drainage, and air pollution from dust and methane release. Reclamation efforts and mining regulations vary by country.

Coal is a major energy source worldwide, traditionally used for electricity generation and as a feedstock for steelmaking (coking coal). Other industrial uses include cement production and chemical manufacturing. Global demand is uneven, with large producers and consumers in China, India, the United States, Australia, and parts of Europe. In recent decades, concerns about greenhouse gas emissions and climate policy have driven efforts to reduce coal use and to replace it with lower-emission energy sources. Reserves are concentrated in a few regions and depend on market conditions.