schist

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schist

(shĭst), metamorphic rockrock,
aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
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 having a foliated, or plated, structure called schistosity in which the component flaky minerals are visible to the naked eye. Schists are distinguished from the other foliated rocks, slates and gneisses, by the size of their mineral crystals; these are larger than those of slates, being visible to the naked eye, but smaller than those of gneisses, which are coarsely foliated rocks as opposed to finely foliated, or schistose, rocks. As contrasted with the folia of slates, the folia of schists are rough-surfaced and irregular. Schists split readily along their planes of schistosity, like slates along cleavage lines. Like other foliated rocks, schists owe their origin to the metamorphism of preexisting rocks. The commonest of the schists is mica schist, the essential minerals of which are quartzquartz,
one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2.
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 and micamica
, general term for a large group of minerals, hydrous silicates of aluminum and potassium, often containing magnesium, ferrous iron, ferric iron, sodium, and lithium and more rarely containing barium, chromium, and fluorine.
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 (biotite or muscovite). Other schists are hornblende schist, talc schist, chlorite schist, and graphite schists. Schists are abundant in the Precambrian (Archean and Proterozoic) rocks.

schist

[shist]
(geology)
A large group of coarse-grained metamorphic rocks which readily split into thin plates or slabs as a result of the alignment of lamellar or prismatic minerals.

schist

A rock, the constituent minerals of which have assumed a position in more or less closely parallel layers or folia; due to metamorphic action; used principally for flagging.

schist

any metamorphic rock that can be split into thin layers because its micaceous minerals have become aligned in thin parallel bands
References in periodicals archive ?
Les assemblages de facies a prehnite-actinolite au facies a schistes verts suggerent que le metamorphisme est survenu a une temperature comprise entre 250[degrees]C et 350[degrees]C, et a une pression inferieure a environ 3 kbar (300 MPa).
La Faille des rochers Skerd separe des roches metamorphiques a forte teneur do massif de Connemara de roches metasedimentaires et metavolcaniques d'un facies de schistes verts de l'Ordovicien inferieur.
On a decouvert que les gisements d'emeraude et autres beryls verts sont localises dans la zone de contact separant une zone de schistes a phlogopite et de veines intrusives de quartz, d'une zone de pegmatites.
Elle avait initialement subi un metamorphisme jusqu'au facies amphibolitique inferieur et elle a plus tard regresse a un facies de schistes verts bas.
Elle s'est seulement metamorphisee jusqu'a un facies de schistes verts bas, possiblement au cours des memes circonstances que celles ou a regresse Ia Formation de Seven Hundred Acre Island.
Parmi les autres lithologies exotiques, d'origine lointaine, on a trouve plusieurs blocs d'anorthosite dont certains de taille metrique; quelques dizaines de cailloux de calcaire fossillifere de Trenton (Ordovicien); beaucoup de quartzites blancs ou roses, et quelques roches ferriferes; deux blocs de coglomerat A clastes calcaires apparemment appalachiens et quelques autres a galets de quartz ainsi que deux blocs de schistes appalachiens, l'un gris, l'autre rouge.