pumice

ALASKA VOLCANO OBSERVATORY GLOSSARY
Light-colored, frothy volcanic rock, usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. Commonly seen as lumps or fragments of pea-size and larger, but can also occur abundantly as ash-sized particles.
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GLOSSARY OF VOLCANIC TERMS
Solidified fragments of quenched, highly vesicular (>60%) silicic magma or lava (Cashman et al., 2000, p. 421). The highly vesicular nature of pumice results from large volumes of gas rapidly expanding within a rapidly cooling magma. The low density of pumice commonly permits it to float on water for extended periods of time. Hot pumice, however, has been shown experimentally to sink rapidly upon interacting with water (Whitham and Sparks, 1986 ).
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USGS PHOTO GLOSSARY OF VOLCANIC TERMS
Pumice is a light, porous volcanic rock that forms during explosive eruptions. It resembles a sponge because it consists of a network of gas bubbles frozen amidst fragile volcanic glass and minerals. All types of magma (basalt, andesite, dacite, and rhyolite) will form pumice.
Pumice is similar to the liquid foam generated when a bottle of pressurized soda is opened--the opening depressurizes the soda and enables dissolved carbon dioxide gas to escape or erupt through the opening. During an explosive eruption, volcanic gases dissolved in the liquid portion of magma also expand rapidly to create a foam or froth; in the case of pumice, the liquid part of the froth quickly solidifies to glass around the gas bubbles.
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Photograph by W.E. Scott on 27 June 1991
Dacitic pumice fragments erupted by Mount Pinatubo, Philippines, during an enormous eruption on 15 June 1991.

Glossary of volcanic terms. - University of Wisconsin Oshkosh. . 2001.

Look at other dictionaries:

  • Pumice — is a textural term for a volcanic rock that is a solidified frothy lava composed of highly microvesicular glass pyroclastic with very thin, translucent bubble walls of extrusive igneous rock. It is commonly, but not exclusively of silicic or… …   Wikipedia

  • pumice — UK [ˈpʌmɪs] / US or pumice stone UK / US noun Word forms pumice : singular pumice plural pumices a) [uncountable] a very light grey stone from a volcano b) [countable] a piece of this stone that you use for rubbing your skin clean and smooth …   English dictionary

  • pumice — [pum′is] n. [ME pomis < OFr < L pumex < IE base * (s)poimno , FOAM] an extremely porous, glassy, extrusive igneous rock typically light enough to float on water, used as an abrasive and in making soaps, polishes, etc.: also pumice stone… …   English World dictionary

  • Pumice — Pum ice, n. [L. pumex, pumicis, prob. akin to spuma foam: cf. AS. pumic st[=a]n. Cf. {Pounce} a powder, {Spume}.] (Min.) A very light porous volcanic scoria, usually of a gray color, the pores of which are capillary and parallel, giving it a… …   The Collaborative International Dictionary of English

  • pumice — c.1400, from O.Fr. pomis (mid 13c.), from L.L. pomex (acc. pomicem, gen. pumicis), from Oscan *poimex, a variant of L. pumex pumice, from PIE *poimo , with connotations of foam, froth. O.E. had pumic stan …   Etymology dictionary

  • púmice — s. m. [Geologia] O mesmo que pomes.   ‣ Etimologia: latim pumix, icis, pedra pomes …   Dicionário da Língua Portuguesa

  • pumice — ► NOUN ▪ a light and porous form of solidified lava, used as a skin abrasive. ORIGIN Old French pomis, from Latin pumex …   English terms dictionary

  • pumice — pumiceous /pyooh mish euhs/, adj. pumicer, n. /pum is/, n., v., pumiced, pumicing. n. 1. Also called pumice stone. a porous or spongy form of volcanic glass, used as an abrasive. v.t. 2. to rub, smooth, clean, etc., with pumice. [bef. 1000; < L… …   Universalium

  • pumice — /ˈpʌməs / (say pumuhs) noun Also, pumice stone. 1. a porous or spongy form of volcanic glass, used, especially when powdered, as an abrasive, etc. –verb (t) (pumiced, pumicing) 2. to rub, smooth, clean, etc., with pumice. {Middle English pomis,… …   Australian English dictionary

  • pumice — 1. noun /ˈpʌmɪs/ 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… …   Wiktionary

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