pumice

Etymology

From Anglo-Norman and Old French pomis (“pumice stone”), from Latin pūmex (“pumice stone”). Doublet of pounce.

noun

1. A light, porous type of pyroclastic igneous rock, formed during explosive volcanic eruptions when liquid lava is ejected into water or air as a froth containing masses of gas bubbles, which are frozen into the rock as the lava solidifies.
   The wind blew close to the ground - it rooted among the tussock grass - slithered along the road, so that the white pumice dust swirled in our faces - settled and sifted over us and was like a dry-skin itching for growth on our bodies. 1912, Katherine Mansfield, The Woman at the Store, Oxford World's Classics 2002, page 10

verb

1. (transitive) To abrade or roughen with pumice.