Pŭm'ice, n.

(Synop., § 130), n. [Lat. pumex, pumicis, It. pomice, Sp. piedra pómez, Fr. pierreponce; A-S. pumic-stān, D. puimsteen, N. H. Ger. bimstein, M. H. Ger. pumiz, bimz, O. H. Ger. pumex, pumiz.] A substance frequently ejected from volcanoes, of various colors, as gray, white, reddish-brown, or black; hard, rough, and porous; and so light as to float on water. It appears to consist of parallel fibers, owing to the parallelism and minuteness of the crowded cells. It is supposed to be produced by the disengagement of gas within the lava, while it is in a liquid or plastic state. Dana.