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Phyllite (Precambrian; outcrop along Cabin Creek, Gallatin National Forest, Montana, USA) 11

Phyllite (Precambrian; outcrop along Cabin Creek, Gallatin National Forest, Montana, USA) 11

Phyllite in the Precambrian of 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.

Phyllite is a low- to intermediate-grade, foliated metamorphic rock. It forms by the metamorphism of slate. Phyllite is principally composed of microcrystalline mica and is usually light gray to dark gray to blackish in color. It has a slightly shiny luster in the light, with slightly wrinkled or crinkled foliation planes.

Locality: outcrop along Cabin Creek, north of Route 287 (= Hebgen Lake Road), Gallatin National Forest, southern Gallatin County, southwestern Montana, USA

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Photo taken on 13 August 2018 (© James St. John / Flickr)

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 phyllite, phyllites, precambrian, cabin, creek, gallatin, national, forest, county, montana, metamorphic, rock, rocks, metamorphics
 

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