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scoria vs. pumice

scoria
[skawr-ee-uh, skohr-] / ˈskɔr i ə, ˈskoʊr- /

noun

scoriae plural

  1. Metallurgy. the refuse, dross, or slag left after melting or smelting metal; scum.

  2. Geology. a cinderlike basic cellular lava.

pumice
[puhm-is] / ˈpʌm ɪs /

noun

  1. Also called pumice stone.  a porous or spongy form of volcanic glass, used as an abrasive.

verb (used with object)

pumices, present (3rd person singular) pumiced, past participle, past pumicing present participle

  1. to rub, smooth, clean, etc., with pumice.