Coal

Coal is a combustible black or brownish-black sedimentary rock primarily composed of carbon, along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Formed from the remains of ancient plant material subjected to heat and pressure over millions of years, coal is used primarily as a fuel source for electricity generation and industrial processes. It is classified into four main types based on carbon content and energy potential: lignite, sub-bituminous, bituminous, and anthracite. Despite its economic importance, coal combustion is a major source of greenhouse gas emissions and air pollution.