Solid fuels such as wood, peat, lignite, coal, and other fossil fuels are combustible energy sources formed from ancient plant matter. Coal represents the largest fossil fuel reserves and was instrumental in powering the Industrial Revolution, though its use has declined relatively due to increasing costs. Coal is a sedimentary rock primarily made of carbon that is formed over millions of years from compressed plant material. It exists in various forms from lignite to anthracite depending on its carbon content and energy value. Pakistan has significant coal reserves concentrated in Sindh province.