noun, feminine/pjɛʁ pɔ̃s/plural: pierres ponces
pierre ponce is feminine in French.
pumice (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)
Synonyms: ponce