By extension, sometimes employed as a synonym of anthracite, or of one of its varieties, the slaty glance coal. Also in plural culms, like coals.

a hard form of coal; anthracite.

Coal of a hard, dense, non-bituminous variety that consists of relatively pure carbon and burns with little flame and smoke; (as a count noun) an…

Non-bituminous coal, or anthracite, which burns without flame.

a variety of anthracite (German glanzkohle, Dutch glanskool).

an Irish name for anthracite.