File:Chiastolite schist (near Mariposa, Mariposa County, California, USA) (27019690877).jpg

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Chiastolite schist from California, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, 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 sample shown here is chiastolite schist from California. Chiastolite is Al2SiO5 - aluminum silicate (see: <a href="https://www.flickr.com/photos/jsjgeology/34576177802">www.flickr.com/photos/jsjgeology/34576177802</a>). It is a "variety" of the mineral andalusite, which is common in some metamorphics.

Locality: unrecorded/undisclosed site near Mariposa, Mariposa County, Sierra Nevada Mountains, central California, USA
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Source Chiastolite schist (near Mariposa, Mariposa County, California, USA)
Author James St. John

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This file is licensed under the Creative Commons Attribution 2.0 Generic license.
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/27019690877 (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.

2 December 2019

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Date/TimeThumbnailDimensionsUserComment
current06:23, 2 December 2019Thumbnail for version as of 06:23, 2 December 20192,237 × 1,475 (2.11 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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