Geologic Time

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon rich, and harder material. The four ranks are:
Coal is primarily used as fuel to generate electric power in the United States. The coal is burned and the heat given off is used to convert water into steam, which drives a turbine.
Coal is a sedimentary rock made predominantly of carbon that can be burned for fuel.
The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons o
The United States has the largest proven coal reserves, with an estimated 260.5 billion short tons of coal in 2008, according to the U.S. Energy Information Administration. Learn More: