| Revision as of 04:56, 2 June 2005 editDarrien (talk | contribs)2,054 editsm Fix image.← Previous edit | Revision as of 17:26, 3 June 2005 edit undoRussBot (talk | contribs)Bots1,405,750 editsm Robot-assisted disambiguation: RomanNext edit → | ||
| Line 6: | Line 6: | ||
| ] volcano on ], ]. Density of specimen approx 0.25 ]/]. Scale is in ].]] | ] 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. | ||
| {{mineral-stub}} | {{mineral-stub}} | ||
Revision as of 17:26, 3 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.
 | This article about a specific mineral or mineraloid is a stub. You can help Misplaced Pages by expanding it. |