Anthracite is an example of a metaphoric rock. Also called hard coal, it is the most highly metamorphosed form of coal. It contains more fixed carbon (86 percent or greater on a dry, ash-free basis) than any other form of coal and the least amount of volatile matter.
Moreover, Anthracite has calorific values near 35 mega-joules per kilogram (approximately 15,000 British thermal units per pound), not much different from the calorific values for most bituminous coal. Anthracite is the least plentiful form of coal. Smaller amounts of anthracite occur in South Africa, Australia, western Canada, China, and other countries.
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