Scoria

Highly vesicular basalt or basaltic glass

i. A bomb-size pyroclast that is highly irregular in form and generally very vesicular. It is similar to pumice, but is usually heavier, darker, and more crystalline.

ii. In less restricted usage, a vesicular cindery crust on the surface of andesitic or basaltic lava, the vesicular nature of which is due to the escape of volcanic gases before solidification. Cinder is sometimes used synonymously.

iii. A local term for melted or partly melted rock (buchite) surrounding burned-out coal beds in the Western United States.

The adj. form, scoriaceous, is usually applied to vesicular pyroclastic ejecta.

See Also: clinker