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, volcanic glass formed by the solidification of lava that is permeated with gas bubbles. Usually found at the surface of a lava flow, it is colorless or light gray and has the general appearance of a rock froth.
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Vesicular, cindery, dark lava formed by the escape and expansion of gases in basaltic or andesitic magma; generally denser and darker than pumice.
Refuse after melting metals or reducing ore.
1. A dark, cellular volcanic rock.
2. Blast-furnace slag or scum.
1. a rough cindery crust on top of solidified lava flows containing numerous vesicles
2. refuse obtained from smelted ore; slag