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| ], below that is pumice and in lower right hand color is ] (light color).]] | ], below that is pumice and in lower right hand color is ] (light color).]] | ||
| '''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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Revision as of 12:46, 19 October 2004
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.
on Tenerife, Canary Islands. Density of specimen
approx 0.25 g/cm³. Scale in centimetres.
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.
When used as an additive for cement, fine-grained version of pumice called pozzolan is mixed with lime to form a light-weight, smooth, plaster-like concrete. This form of concrete was used as far back as Roman times.
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