\Pum"ice\, n. [L. pumex, pumicis, prob. akin to spuma
foam: cf. AS. pumic-st[=a]n. Cf. {Pounce} a powder, {Spume}.]
(Min.)
A very light porous volcanic scoria, usually of a gray color,
the pores of which are capillary and parallel, giving it a
fibrous structure. It is supposed to be produced by the
disengagement of watery vapor without liquid or plastic lava.
It is much used, esp. in the form of powder, for smoothing
and polishing. Called also {pumice stone}.