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| '''Pumice''' is a light, porous type of ] ]. It is formed during explosive ] eruptions when liquid ] is ejected into the air as a froth containing masses of gas bubbles. As the lava solidifies, the bubbles are frozen into the rock. Any type of igneous rock - ], ], ] or ] - can form pumice given suitable eruptive conditions. | '''Pumice''' is a light, porous type of ] ]. It is formed during explosive ] eruptions when liquid ] is ejected into the air as a froth containing masses of gas bubbles. As the lava solidifies, the bubbles are frozen into the rock. Any type of igneous rock - ], ], ] or ] - can form pumice given suitable eruptive conditions. | ||
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| <small>''Specimen of highly porous pumice from ] volcano on ], ]. Density of specimen approx 0.25 ]/]. Scale in ]s.''</small></div> | |||
| It is considered a ] because it has no crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in ]. It is widely used to make lightweight ] and as an ], especially in polishes and ] exfoliants. | It is considered a ] because it has no crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in ]. It is widely used to make lightweight ] and as an ], especially in polishes and ] exfoliants. | ||
Revision as of 12:31, 12 April 2004
File:Different rocks at Panum Crater-300px.jpg
Top stone is obsidian, below that is pumice
and in lower right hand color is rhyolite (light color)
Pumice is a light, porous type of pyroclastic igneous rock. It is 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. Any type of igneous rock - andesite, basalt, dacite or rhyolite - can form pumice given suitable eruptive conditions.
It is considered a glass because it has no crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in water. It is widely used to make lightweight concrete and as an abrasive, especially in polishes and cosmetic exfoliants.
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