People use coal to generate power. This power has served various purposes over the years, from powering steam engines to warming homes to providing electricity for manufacturing. Though many people understand generally what coal is, few understand the actual characteristics of coal, how it came to exist, what it's composed of and how it's specifically used. Identifying and describing the characteristics of coal requires a detailed examination of the timeline over which coal is formed.
Though most people typically associate coal with the color black, coal can range in colors from shiny silver to green. Coal’s color typically relates to its specific forms, which in turn relate to how “new” the coal is. A deep-black color indicates that the coal is quite old -- darkened and compacted by millions of years of pressure. Lighter browns and greens indicate young coal that is as of yet compacted and darkened by the tremendous pressure of the earth’s surface and gravity.
Traditionally, people think of coal as a hard rock. In actually, coal can be quite brittle and, in some cases, even spongy. As with color, the texture of coal typically reflects its age. Harder coals reflect years and years of compacting, while softer and lighter coals still maintain some of the pockets of air and other materials that have yet to be squeezed out of them.
The primary chemical found in coal is carbon, specifically in older coals. Old coals such as anthracite and graphite feature the highest amount of carbons, percentage-wise, mostly due to the ways in which pressures worked to squeeze out other chemicals. Younger coals, however, such as peat or lignite feature trace chemical elements of hydrogen, sulfur, nitrogen and even oxygen.
The youngest or newest form of coal is peat. Peat is essentially the vegetative and soil matter that, if compressed for millions of years, would eventually produce coal. Lignite and sub-bituminous coal are the second and third youngest coals, respectively. Bituminous, steam coal and anthracite form the next grouping of coal, ordered from youngest to oldest. And finally, graphite is the oldest form of coal.