Humans use coal in many ways, including as a fuel and as a source of carbon. As a solid fuel, coal burns to provide heat from stoves, furnaces and boilers as well as energy to supply electrical generating plants. Metal refiners use coke, a solid residue from low-sulfur bituminous coal, in purifying metals in blast furnaces.
Coal, like petroleum, is a fossil fuel. It has a very long history of use in homes and industry. Coal differs from other rocks in that it consists of organic carbon rather than mineralized solids. It forms under special conditions where dead plant material forms in layers covered in water and mud, preventing the carbon in them from oxidizing. Coal remains in a chemically reduced form ready for oxidation. Oxidation of coal, known as burning, produces heat. It is this source of energy that man often finds useful.
The use of coal is not without problems. Mining endangers the lives of humans who work in the mines. Open-pit mining leads to environmental concerns. Inextinguishable coal fires burn in underground coal beds around the world, creating problems for those who live nearby. Coal use is the leading source of carbon dioxide emissions to the atmosphere, contributing to harmful levels of pollution.