Muscovite schist (Paleoproterozoic; Black Hills, South Dakota, USA) 6 : 無料・フリー素材/写真
Muscovite schist (Paleoproterozoic; Black Hills, South Dakota, USA) 6 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Muscovite schist from the Precambrian of South Dakota, USA.Metamorphic rocks result from intense alteration of any previously existing rocks by heat and/or pressure and/or chemical change. This can happen as a result of regional metamorphism (large-scale tectonic events, such as continental collision or subduction), burial metamorphism (super-deep burial), contact metamorphism (by the heat & chemicals from nearby magma or lava), hydrothermal metamorphism (by superheated groundwater), shear metamorphism (in or near a fault zone), or shock metamorphism (by an impact event). Other categories include thermal metamorphism, kinetic metamorphism, and nuclear metamorphism. Many metamorphic rocks have a foliated texture, but some are crystalline or glassy.Schist is an intermediate- to high-grade, foliated metamorphic rock. It is highly variable in appearance, depending on the mineral content, which is a function of the precursor rock and specific temperature-pressure conditions. Garden-variety schists form by metamorphism of phyllites. Schists typically have medium- to large-sized crystals, unlike the microcrystalline nature of slate & phyllite.Schist's foliated texture (= crystals aligned into bands or stripes or layers) is often only seen when specimens are viewed on edge.The muscovite schist shown above is a common variety of mica schist. The scattered black crystals appear to be hornblende amphibole. The foliation here is nicely crinkled.Age: apparently late Paleoproterozoic, ~1.7 GaLocality: roadside loose piece next to the White Cap Mine and Edison Mine, east of the town of Keystone, eastern Black Hills, western South Dakota, USA |
| 撮影日 | 2017-01-13 10:58:44 |
| 撮影者 | James St. John |
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