10 Types of coal

1. Lignite or brown coal - lowest rank of coal. Used almost exclusively as fuel for electric power generation.

2. Jet - compact form of lignite. Sometimes polished and used as an ornamental stone.

3. Sub-bituminous coal - properties range from those of lignite to those of bituminous coal. Used primarily as fuel for steam-electric power generation. Important source of light aromatic hydrocarbons for the chemical synthesis industry.

4. Smithing coal - type of high quality bituminous coal.* Ideally suited to use in a coal forge. It is as free from ash, sulphur and other impurities as possible.

5. Cannel coal - also bituminous*. Ignites easily producing a bright flame. The name derives from "candle coal". Contains a high volatile content and is non-coking. Use has greatly diminished over the past century but still valued by artists for its ability to be carved and polished into sculptures and jewellery.

6. Coking coal - when used for many industrial processes, bituminous coal must first be "coked" to remove volatile components. Coking coal is heated to produce coke, a hard, grey, porous material which is used to blast in furnaces for the extraction of iron from the iron ore. Coking is achieved by heating the coal in the absence of oxygen. This drives off volatile hydrocarbons (propane, benzene, etc) and some sulphur gases, also drives a considerable amount of the contained water in it. Coking coal is used in the manufacture of steel, where carbon must be as volatile-free and ash-free as possible.

(* ie - a dense sedimentary rock, usually black, sometimes dark brown, often with well-defined bands of bright and dull material).

7. "Steam coal"- midway between bituminous coal and anthracite, once widely used as a fuel for steam locomotives. In this specialised use, it is sometimes known as "sea-coal" (US). Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating.

8. Anthracite - highest rank of coal. A harder, glossy black coal used primarily for residential and commercial space heating. Can be divided further into metamorphically altered bituminous coal and "petrified oil". Other terms for it - black, hard or stone coal (not to be confused with German Steinkohle, Dutch steenkool, broader terms meaning all varieties of coal of a stonelike hardness and appearance), blind coal (Scotland), Kilkenny coal (Ireland), crow or craw coal (from its shiny black appearance) and black diamond.

9. Culm - imperfect anthracite of north Devon and Cornwall (around Bude) which is used as a pigment.

10. Graphite - technically the highest rank, is difficult to ignite and is not commonly used as fuel -  it is mostly used in pencils and, when powdered, as a lubricant.