History

About 300 million years ago, enormous ferns and other prehistoric plants were common on the swamp-like earth. When those plants died and fell to the ground, they were covered with water and they slowly decomposed. As decomposition took place in the absence of oxygen, much of the hydrogen content of the matter was eroded away, leaving a material rich in carbon. The material was compressed over the years by sand and dirt, leaving the form of carbon known as coal.

Types

The nature of coal is such that the higher the carbon content, the more cleanly and brilliantly the coal burns. Thus "peat", which is the state of the decomposing plants before being compressed, is a weak, impure substance. The other states of coal, from lowest carbon content to highest, are "lignite," bituminous coal, and anthracite coal. If the coal is heated and compressed even more, the result is "graphite," almost completely pure carbon.

Nearly all the different forms of coal are used in some way or another. For instance, peat has been used for burning in furnaces, whereas bituminous coal is used extensively for the generation of electricity. "Coke," a very pure form of coal with a high heat content is used primarily in the steel industry, where high temperatures are required.