View source for Phyllite

{{Short description|Type of foliated metamorphic rock}}
[[File:Phyllite Cenulation.jpg|Phyllite|thumb]]
[[File:Fylite-micro.jpg|thumb|[[Photomicrograph]] of [[thin section]] of phyllite (in cross [[Polarization (waves)|polarised]] light)]]
[[File:DukeStone2.jpg|thumb|Fractured [[Duke_University#Duke_stone | Duke stone]] showing phyllitic texture]]
[[File:PhylliteUSGOV.jpg|thumb|Phyllite]]

'''Phyllite''' ({{IPAc-en|ˈ|f|ɪ|l|aɪ|t}} {{respell|FIL|yte}}) is a type of [[foliation (geology)|foliated]] [[metamorphic rock]] formed from [[slate]] that is further metamorphosed so that very fine grained white [[mica]] achieves a preferred orientation.<ref name=EG>Stephen Marshak ''Essentials of Geology'', 3rd ed.</ref> It is primarily composed of [[quartz]], [[sericite]] [[mica]], and [[chlorite group|chlorite]].<ref>Mottana, Annibale, Rodolfo Crespi and Giuseppe Liborio (1978) ''Simon & Schuster's Guide to Rocks and Minerals''. New York: Simon & Schuster Inc.</ref>

Phyllite has fine-grained mica flakes, whereas [[slate]] has extremely fine mica flakes, and [[schist]] has large mica flakes, all mica flakes of which have achieved a preferred orientation.<ref name=EG/> Among foliated metamorphic rocks, it represents a gradation in the degree of [[metamorphism]] between slate and schist.{{citation needed|date=March 2013}}

The minute crystals of [[graphite]],<ref>Schumann, Walter, (1993) ''Handbook of Rocks, Minerals, & Gemstones''. Boston & New York: Houghton Mifflin Company.</ref> sericite, or chlorite, or the [[translucent]] fine-grained white mica,<ref name=EG/> impart a silky,<ref name=EG/> sometimes golden{{citation needed|date=March 2013}} sheen to the surfaces of [[cleavage (geology)|cleavage]], called "phyllitic luster".<ref name=EG/>

The word comes from the Greek ''phyllon'', meaning "leaf".<ref name=EG/>

The [[protolith]] (or parent rock) for phyllite is [[shale]] or [[pelite]]; or slate, which in turn came from a shale protolith. Its constituent platy minerals are larger than those in slate but are not visible with the naked eye. Phyllites are said to have a texture called "phyllitic sheen," and are usually classified as having formed through low-grade metamorphic conditions through regional metamorphism [[metamorphic facies]].

Phyllite has good [[Fissility (geology)|fissility]] (a tendency to split into sheets). Phyllites are usually black to gray or light greenish gray in color. The foliation is commonly crinkled or wavy in appearance. Phyllites are mostly used in decorative aggregates, interior decors, building stones, facing stones, garden decoration and curbing. Cemetery markers, commemorative tablets, creating artworks and writing slates are some of its commercial uses.

Phyllite is commonly found in the [[Dalradian]] metasediments of northwest [[Isle of Arran|Arran]]. In north Cornwall, there are Tredorn phyllites and Woolgarden phyllites.<ref>Barton, R. M. (1964) ''An Introduction to the Geology of Cornwall''. Truro: D. Bradford Barton; p. 89</ref>{{Self-published inline|date=July 2021}}

Carolina "slate" is often volcanic phyllite. A type of Carolina slate, [[Duke_University#Duke_stone | Duke stone]], is a dacitic phyllite that is fractured and colored with iron oxide.

==References==
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==External links==
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{{Commons category|Phyllite}}
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[[Category:Metamorphic rocks]]


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