pumice

A light, porous, glassy lava, used in solid form as an abrasive and in powdered form as a polish and an abrasive.

To clean, polish, or smooth with pumice.

To polish, rub, or otherwise treat with pumicestone; especially, in silver-plating, to clean with pumice and water, as the surface of an article to be plated.

Lava having a loose, spongy or cellular structure; lava from which gas or steam has escaped in large quantities while it was becoming consolidated.

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.

A light, porous type of pyroclastic igneous rock, formed during explosive volcanic eruptions when liquid lava is ejected into the air as a froth containing masses of gas bubbles. As the lava solidifies, the bubbles are frozen into the rock.

To abrade or roughen with pumice.

rub with pumice, in order to clean or to smoothen

a light glass formed on the surface of some lavas; used as an abrasive