Coal

Coal is a fossil fuel primarily composed of carbon and hydrocarbons. Combined with potassium nitrate and sulfur, coal may be used as a component in gunpowder.

The 20th century Vulcan explorer Mestral found employment as a coal miner following his crash-landing on Earth at Carbon Creek. (ENT: "Carbon Creek")

Captain James Kirk and Doctor Leonard McCoy discovered in 2267 that the people of Neural, with Klingon technical assistance, had learned to use coal to forge flintlocks and sulfur to manufacture gunpowder. (TOS: "A Private Little War")

Dr. McCoy complained in 2268, that he was "...a doctor, not a coal miner." (TOS: "The Empath")