retaxis
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Coal is a combustible sedimentary rock classified into four main types—or ranks—based on the amount of pressure, heat, and time it has undergone underground. This maturation process is called coalification, where higher ranks contain more carbon and energy, and less moisture. [1, 2, 3, 4, 5]
According to the U.S. Geological Survey and the U.S. Energy Information Administration, the four main types from lowest rank to highest rank are: [1, 2]
1. Lignite
2. Subbituminous
3. Bituminous
4. Anthracite
According to the U.S. Geological Survey and the U.S. Energy Information Administration, the four main types from lowest rank to highest rank are: [1, 2]
1. Lignite
2. Subbituminous
- Carbon Content: 35% to 45%
- Characteristics: Dull, black-colored coal with higher moisture and lower energy content than bituminous coal.
3. Bituminous
- Carbon Content: 45% to 86%
- Characteristics: Often called "soft coal", it is a dense, dark rock that usually features a shiny, layered texture. It is the most abundant type of coal.
4. Anthracite
- Carbon Content: 86% to 97%
- Characteristics: Known as "hard coal", it is the highest rank of coal. It is dense, brittle, has a shiny black luster, and burns hottest and cleanest with very little smoke.



