There are four types of coal in order highest energy content to lowest energy content.
- Anthracite: This is the highest ranked, hardest, oldest, and least common type of coal. It possesses a high energy content, high percentage of carbon (>85%) and relatively little moisture or volatiles.
- Bituminous: This is the second rank of coal, softer and younger than anthracite, and containing a lower percentage of carbon (45-85%) and therefore more moisture and volatiles.
- Subbituminous: This is the third rank of coal, possessing 35-45% carbon and more moisture than bituminous coal.
- Lignite: This is the softest, youngest, and wettest rank of coal, often referred to as "brown coal" with a carbon content of only 25-35% and correspondingly lower energy content.
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