What are the coal classes and what makes them different?

What are the coal classes and what makes them different?

• A. Lignite, Subbituminous, Bituminous, Anthracite
• B. Lignite, Bituminous, Subbituminous, Anthracite
• C. Anthracite, Bituminous, Subbituminous, Lignite
• D. Subbituminous, Lignite, Anthracite, Bituminous

Answer: (C)

Coal is categorized by rank, which means its maturity from heat and pressure over geological time. As rank increases, carbon content and heating value rise, while moisture and volatile matter generally decrease. Anthracite is the most mature with the highest carbon content and energy, followed by bituminous, then subbituminous, and finally lignite, which has the lowest carbon content and energy. This order—from most to least mature—best reflects how these classes differ. The other sequences mix the order of subbituminous and bituminous or misplace lignite, so they don’t align with the actual progression of coal rank.

Coal is categorized by rank, which means its maturity from heat and pressure over geological time. As rank increases, carbon content and heating value rise, while moisture and volatile matter generally decrease. Anthracite is the most mature with the highest carbon content and energy, followed by bituminous, then subbituminous, and finally lignite, which has the lowest carbon content and energy. This order—from most to least mature—best reflects how these classes differ. The other sequences mix the order of subbituminous and bituminous or misplace lignite, so they don’t align with the actual progression of coal rank.