volcanictuff

As a noun pumice is

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.

As a verb pumice is

to abrade or roughen with pumice.

As a noun lapilli is

a sphere shaped droplet of molten lava ejected from a volcanic eruption which falls to earth while still at least partially molten, ranging in size from 2 to 64 millimeters.