pum·ice 
(pŭmĭs)
(pŭmĭs)n.
A light, porous, glassy lava, used in solid form as an abrasive and in powdered form as a polish and an abrasive.
tr.v. pum·iced, pum·ic·ing, pum·ic·es
To clean, polish, or smooth with pumice.
[Middle English, from Anglo-Norman pomis, from Late Latin pōmex, from Latin pūmex, alteration of spūma, foam.]
pu·miceous (py-mĭshəs, pə-) adj.
pumic·er n.