coke

Coke is a grey, hard, and porous coal-based fuel with a high carbon content. It is made by heating coal or petroleum in the absence of air. Coke is an important industrial product, used mainly in the smelting of iron ore, but also as a fuel in stoves and forges.
The unqualified term "coke" usually refers to the product derived from low-ash and low-sulphur bituminous coal by a process called coking. A similar product called petroleum coke, or pet coke, is obtained from crude petroleum in petroleum refineries. Coke may also be formed naturally by geologic processes. It is the residue of a destructive distillation process.

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