English: "Coke" refers to multiple materials. It can be the fizzy sugar water that rots teeth. It can be the illegal white powder that losers use to kill their own brain cells. It can also be a manmade fuel, of which a specimen is seen here.

Coke looks somewhat like volcanic scoria - it is dark-colored, light-weight, and frothy-textured. Coke is manufactured by heating coal in the absence of oxygen, so it doesn't burn. Volatile organic compounds leave the coal, resulting in coke. Compositionally, coke is rich in carbon (close to anthracite coal), with minor impurities, plus ash (= microscopic mineral matter that doesn't burn).

Once made, coke can be used as a smokeless, much hotter-burning fuel. It is principally used as a source of heat and a reducing agent in steel-making factories (iron ore gets converted to elemental iron).

Locality: trackside (loose piece dropped from a passing train), Marion Station, Marion, Ohio, USA

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See info. at:

en.wikipedia.org/wiki/Coke_(fuel)