What Is Coal?
Coal is a solid hydrocarbon formed from plants in the geological past and preserved by burial under various sedimentary rocks. The preservation process begins with the breakdown of the plant material by the actions of bacteria and fungi followed by progressively deeper burial that initially squeezes out water and ultimately drives out gases such as CO2 and CH4 as ground temperatures rise. Coal is a mixture of organic matter, mineral matter (clays and quartz mostly) and water. Only the organic matter contains the energy of the coal, the mineral matter contains no energy and the water normally requires energy to vapourise it. The organic matter is composed of both volatile matter (gases and oils) that is given off on heating the coal, the other organic component of coal is called fixed carbon. The ratio of fixed carbon to volatile matter increases as the depth of burial increases and this is described as an increase in coal rank.
Steeply dipping coal seams at the Adaro Opencut mine in Kalimantan Indonesia