Coal consists of a complex range of materials, and coal from one deposit may differ greatly from that of another. These differences result from the varying types of vegetation from which the coal originated; the depths of burial, and the temperatures and pressures at those depths; as well as the length of time the coal has been forming in the deposit. The varying amount of mineral matter in a coal deposit may also have a significant effect on its properties and classification.

Coal is generally classified by what is known as "rank". Ranking is determined by the degree of transformation of the original plant material to carbon. The ranks of coals, from those with the least carbon to those with the most carbon, are lignite, sub-bituminous, bituminous and anthracite.

In addition to carbon, coals contain hydrogen, oxygen, nitrogen and varying amounts of sulphur. High-rank coals are high in carbon and therefore heat value, but low in hydrogen and oxygen. Low-rank coals are low in carbon but high in hydrogen and oxygen content.

The highest rank, and hardest coal, is anthracite. It is found almost exclusively in remote regions of northern British Columbia and the Yukon. Anthracite is not being mined in Canada at present.

Bituminous coal, ranked second highest, is found in Alberta, British Columbia and the Maritimes. Bituminous coal can be metallurgical -- used to make coke for the steel industry -- or thermal, used to generate electricity. In 2002, bituminous coal accounted for 29.7 million tonnes (Mt) or approximately 45% of Canada's total coal production.

Sub-bituminous coal is softer than bituminous and contains more moisture, making it less economic to transport long distances. Alberta is the only province where sub-bituminous coal is mined. In 2001, 25.4 Mt were produced to generate over 70% of the province's electricity.

Lignite is a soft, brown or black coal found in southern Saskatchewan, southeastern Alberta and southwestern Manitoba. Only the Saskatchewan deposits are currently being mined and production is used to generate approximately 70% the province's electricity. In 2001, 11.4 Mt of lignite coal were produced in Saskatchewan.

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