File:Soapstone with manganese oxide dendrites (Mesoproterozoic, 1.1 to 1.3 Ga; near Ennis, Montana, USA) 1 (49147054227).jpg
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Soapstone from the Precambrian of Montana, USA. (public display, Montana Bureau of Mines & Geology Mineral Museum, Butte, Montana, 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. Soapstones are crystalline-textured, talc-rich metamorphic rocks. Essentially pure talcose soapstone is called steatite, whereas "soapstone" refers to impure varieties. “Soapstone” and “steatite” are sometimes considered synonyms. Being composed of talc (magnesium hydroxy-silicate - Mg3Si4O10(OH)2), steatite and soapstone have a soapy feel and are very soft - they are easily scratched. This southwestern Montana soapstone sample has abundant black manganese oxide dendrites. Such features can be common along beddings planes and joint surfaces. Talc "deposits" in southwestern Montana are hosted by Archean marbles. The talc formed by multiphasic metamorphism involving hydrothermal magnesium metasomatism of marble, replacement, deformation, and recrystallization. The hot fluids that formed the talc were associated with intrusive activity during the late Mesoproterozoic, about 1.1 to 1.3 billion years ago Locality: unrecorded/undisclosed site (probably a talc mine) near Ennis, southwestern Montana, USA Site-specific details synthesized from info. provided by Childs Geoscience Incorporated (Bozeman, Montana) |
| Date | |
| Source | Soapstone with manganese oxide dendrites (Mesoproterozoic, 1.1 to 1.3 Ga; near Ennis, Montana, USA) 1 |
| 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@N05/49147054227 (archive). It was reviewed on 30 November 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 | 17:06, 30 November 2019 | | 1,739 × 1,504 (2.31 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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