Coal and its uses
Coal is a complex resource and can vary in composition even within the same deposit. Generally, there are four different types or ranking levels of coal, each with differences in energy output as a result of increased pressurization, heat, and time.

 

Ligiten

This is a brownish-black coal with high moisture and ash content, which has the lowest heating value of the four types of coal. It is considered an “immature” coal that is still soft. It is used for generating electricity.

 

Subbituminous

This is a dull black coal with a higher heating value than lignite, and is used principally for electricity and space heating.

 

Bituminous

This is the most common type. It is the most commonly used type of coal for electric power generation. It is a dark, hard coal that has a higher heating value than lignite and subbituminous coal, but a lower heating value than anthracite.

 

Anthracite

This is also known as "hard coal" that was formed from bituminous coal under increased pressures in rock strata during the creation of mountain ranges. It is very hard and shiny. This type of coal is the most compact and therefore, has the highest energy content of the four levels of coal. It is used for space heating and generating electricity.