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| ⚫ | ] volcano on ], ]. Density of specimen approx 0.25 ]/]. Scale is in ].]] | ||
| ], 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. When larger amounts of gas are present, the result is a finer-grained variety of pumice known as '''pumicite'''. | '''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. When larger amounts of gas are present, the result is a finer-grained variety of pumice known as '''pumicite'''. | ||
| 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. | ||
| ⚫ | ] volcano on ], ]. Density of specimen approx 0.25 ]/]. Scale is in ].]] | ||
| When used as an additive for ], a fine-grained version of pumice called ] is mixed with ] to form a light-weight, smooth, plaster-like ]. This form of concrete was used as far back as ] times. | When used as an additive for ], a fine-grained version of pumice called ] is mixed with ] to form a light-weight, smooth, plaster-like ]. This form of concrete was used as far back as ] times. | ||
Revision as of 10:28, 5 June 2005
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. When larger amounts of gas are present, the result is a finer-grained variety of pumice known as pumicite.
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, a 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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