Upon this rests a pumiceous breccia and conglomerate, with angular masses of trachyte, and some quartz pebbles.
It filled ravines, such as Fosso Grande, and concreted and hardened there into pumiceous tufa—a very instructive phenomenon.
All the upper part of the mountain is composed of a pumiceous tufa, rich in sanidine and of a characteristic greenish colour.
c.1400, from Anglo-French and Old French pomis (13c.), from Late Latin pomicem (nominative pomex, genitive pumicis), from Oscan *poimex or some other dialectal variant of Latin pumex "pumice," from PIE *(s)poi-mo-, a root with connotations of "foam, froth" (see foam (n.)). Old English had pumic-stan. As a verb, early 15c., from the noun.
pumice pum·ice (pŭm'ĭs)
A light, porous, glassy lava, used as an abrasive.