| 词汇 | gneiss |
| 释义 | gneiss noun[ U ] geology specializeduk /naɪs/ us /naɪs/ a type of metamorphic rock that contains light and dark layers formed of minerals such as quartz and mica片麻岩（由长石﹑石英组成﹐中粗粒变晶结构和片麻状或条带状构造的变质岩） mikeuk /iStock/Getty Images Plus/GettyImages Geology: types of rock agglomerate arenaceous arenite asthenosphere asthenospheric emery flinty haematite indurated intrusive lahar limestone lodestone magma marcasite marl marmoreal obsidian sandstone schist Examples of gneissgneiss Here we describe the colonization of heavily shocked gneiss by heterotrophic bacteria in a natural setting. The country rock was typically coarse crystalline granite gneiss, strongly weathered, ventifacted, and partly polished, and outcrops were 'crumbled' and without strength. In weakly deformed gneiss, the mafic minerals (biotite, augite and hornblende) occur as irregular clusters, locally separated from plagioclase by coronas of garnet. Samples from the normal smooth surface of the gneiss boulder show that the surface has been ground and polished during glacial transportation. These gneisses have been multiply deformed at granulite-facies conditions. In general, eclogites are predominantly mafic and are preserved as boudins within felsic gneisses. These pass up into a 150 m thick homogeneous granite that is bound by planar surfaces parallel to the foliation in the underlying gneiss. The kinematic evidence is interpreted to mean that the contact between the gneiss and the biotite schist has a normal-shear (hangingwall down) geometry. To the south, the meta-gabbro is bounded by felsic gneiss. There is a continuum apparent between the amphibolites and intermediate gneisses, whilst the felsic gneisses form a separate, high-silica group. However, few recognizable trends are apparent within the data clusters for the siliceous gneisses. In thin-sections, the gneisses are cut by narrow pressure solution seams and narrow cataclastic shear zones. 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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