Coke

Coke was an uncommon form of highly refined fuel distilled from coal or petroleum.

Properties
Coke was a gray, carbon-rich mineral-like substance that burned readily, with similarities to charcoal. It was about as heavy as coal, weighing between to  per.

Availability
Coke was normally processed from coal in an oven, but could also be found naturally as "igneous coke" when underground heat and pressure acted on underground deposits.

Usage

 * Coke fuel was normally used for high-quality metalworking projects.
 * Igneous coke was a viable material for making light pellets.
 * Purifying fire used a sample of coke.