File:Chlorite schist (Wissahickon Schist, Neoproterozoic to Cambrian; Jarrettsville, Maryland, USA) (16735383710).jpg
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Chlorite schist from the Neoproterozoic to Cambrian of Maryland, USA. (8.2 centimeters across at its widest) 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. Chlorite schist is a moderately common metamorphic rock. It is principally composed principally of chlorite, a silicate mineral with a greenish to grayish-green color. The sample of chlorite schist (metapelite) shown above is from the Neoproterozoic- to Cambrian-aged Wissahickon Schist of Maryland, USA. Metamorphism took place during the Taconic Orogeny (Late Ordovician to Silurian), which affected much of eastern North America. Chlorite schist can have a component of magnetite (Fe3O4 - iron oxide) (for example, see above specimen), which usually occurs as black, relatively small, octahedral crystals. Stratigraphy: Wissahickon Schist (a.k.a. Wissahickon Formation), Glenarm Series (Glenarm Supergroup), Neoproterozoic to Cambrian; metamorphism in the Late Ordovician to Silurian Locality: Jarrettsville, western Harford County, northeastern Maryland, USA |
| Date | |
| Source | Chlorite schist (Wissahickon Schist, Neoproterozoic to Cambrian; Jarrettsville, Maryland, USA) |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/16735383710 (archive). It was reviewed on 2 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 06:23, 2 December 2019 | | 1,087 × 844 (1.64 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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