Aug 15 - Coal is used to produce 40 percent of the world's electricty, most of its steel and the cement in its buildings and shows no sign of losing popularity.
It is made of old organic matter which has been compressed by rocks over millions of years and there are several types found around the world of varying moisture content and energetic value, factors which largely determine how it is used.
Burning coal produces more carbon dioxide than any other fossil fuel, the main manmade gas blamed for global warming.
Coal quality is determined by pressure, temperature and how long it has been forming, with the oldest and hardest coals drier and more energetic than younger, damper deposits.
Organic matter in peat bogs first transforms over millions of years into lignite or 'brown coal.'
Over millions more years lignite transforms into the range known as `sub-bituminous' coals.
Further blackening and hardening during 'coalification' forms `bituminous' or hard coals. Eventually, under the right conditions, the hardest of coals, anthracite, is formed.
Below is a summary of the different types of coal and what they are used for.
For information on the producers and users of coal, click here [ID:nL15834910]
LOW QUALITY COALS - Softer, wetter, duller, earthier, lower energy content.
LIGNITE - Mostly used to generate power. Demand expected to grow by 1 percent a year through to 2030.
SUB-BITUMINOUS - Power generation, cement making and industries like chemicals and pharmaceuticals.
Coal is not only an ingredient in cement but is also used in large quantities to fire the kilns which bake the material used in many of the world's buildings.
It is also needed to make carbon fibre which is used for strong, light-weight products from bicycles to tennis rackets.
HARDER COALS - Darker, drier, shinier, more energetic
Thermal Steam Coal - used for power generation, cement and other industrial uses. Thermal steam coal demand is expected to grow at at 1.5 percent a year until 2030.
Metallurgical Coking Coal - used to make iron and steel. Demand expected to grow at 0.9 percent a year until 2030.
ANTHRACITE - Relatively clean burning and lightweight for its energy content but expensive. Most often used in domestic coal fires and businesses needing smokeless fuel.
Source: World Coal Institute.