Coal rank

Coal rank refers to the different types of coal classified based on their carbon content, moisture, and energy potential, which result from the coalification process (how coal forms over time). As coal matures through this process, it progresses from lignite (brown and low energy) to sub-bituminous, then bituminous, and finally anthracite (hardest, highest carbon content, and most energy-rich). Higher-rank coals like anthracite generally burn cleaner and produce more energy per weight, while lower-rank coals like lignite contain more moisture and less energy. The rank influences how coal is used and its environmental impact.