Pumice-Stone, a hard fossil, that is frequently ejected from volcanoes : it is very light, with numerous pores, being of a white, grey, reddish-brown, or black co-lour.

This mineral is usefully employed in different mechanical trades, for rubbing, and smoothing or polishing wood, paste-board, metals, and stone ; because, on account of its peculiar roughness and brittle-ness, it effectually removes all inequalities from their surfaces.