Anthracite Wikipedia
Anthracite, also known as hard coal, is a hard, compact variety of coal that has a submetallic has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the highest ranking of coals.. Anthracite is the most metamorphosed type of coal (but still represents lowgrade metamorphism), in which the carbon content is between 86% and 98%.