SRAC Presents: Mineralogy for Kids

Coal : In this episode, Ted Keir tells us about the different types of coal.

Coal
Coal is a solid fuel made from plants that lived between 345 and 280 million years ago. Over time, this vegetation died and became submerged under water, where it gradually decomposed. As time passed, layers of sand and mud settled from the water over the remnants of these plants. The pressure of these overlying layers, as well as movements of the earth's crust, compress and harden the deposits, thus producing coal.

Various types of coal are classified according to fixed carbon content which gets higher as the plant remnants continue to decompose and be pressurized.

Peat, the first stage in the formation of coal, has a low fixed carbon content and a high moisture content. The carbon content is greater in lignite, the lowest rank of coal. Bituminous coal has even more carbon and a correspondingly higher heating value. Anthracite coal has the highest carbon content and heating value. Coal may be transformed by further pressure and heat into graphite that is almost pure carbon.

Other components of coal are volatile hydrocarbons, sulfur and nitrogen, and the minerals that remain as ash when the coal is burned.