| 词汇 | pumice |
| 释义 | pumice noun[ U ] uk /ˈpʌm.ɪs/us a type of grey, light stone that is used in pieces or as a powder for rubbing things to make them smooth: 浮石，轻石（用来摩擦物体使其光滑） Pumice is produced in volcanic eruptions.浮石是在火山爆发中产生的。 DonNichols/iStock/Getty Images Plus/GettyImages Geology: types of rock agglomerate arenaceous arenite asthenosphere asthenospheric emery flinty gneiss indurated intrusive lahar limestone lodestone magma marcasite marl marmoreal obsidian sandstone schist Examples of pumicepumice Concentrations of pumice clasts towards the base form trains of clasts that are traceable along the length of outcrops. Concentrations of accretionary lapilli and diffuse trains of small pumices define bedding in this thick ash bed. For selected ignimbrites, sanidine crystals were taken from fresh, unaltered pumice lapilli. Due to incomplete exposures, the dispersal characteristics of most pumice fallout deposits are poorly constrained. Widely dispersed plinian-type pumice fall deposits and ignimbrite are characteristic products of both explosive cycles. Lithic- and pumice-rich horizons may mark separate eruptive events. The presence of banded pumice near the top defines a compositional zonation of the ignimbrite. These tuffs are all considered to be ash flow deposits because they are unbedded and contain well-developed eutaxitic foliation and pumice pseudomorphs locally. In the sixth zone, an abrupt change to greyish pumice is encountered, and no crystals are seen. Particle-supported autotrophic biofilms were cultivated in external-loop airlift reactors at different pumice concentrations. Concentrations of pumice occur locally in the upper 20-30 cm of the ignimbrite. Lithic fragments are commonly embedded in the larger pumices. The alkali basalt lithic breccias pass abruptly upwards into banded pumice-bearing ignimbrite. The internal structure of the bedforms is massive, although openwork clusters of pumice occur at the crest and on the lee-side. For this purpose biofilms were grown as autotrophic and heterotrophic communities on pumice in an airlift loop reactor. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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