metamorphic rocks


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metamorphic rocks:

see 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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Metamorphic Rocks

 

rocks that formed earlier as sedimentary or igneous rocks but have undergone alteration (metamorphism) in the earth’s interior under the influence of abyssal fluids, temperature, and pressure or alteration near the surface under the influence of the heat of intrusive masses.

Metamorphic rocks formed deep within the earth (products of regional metamorphism) are characterized by schistosity that developed as a result of directional pressure; they are called crystalline schists. As the degree of metamorphism increases, clays are converted to phyllites, mica schists, and gneisses (schisty rocks with a large amount of granite material). Marls and basic igneous rocks are converted to chlorite schists and actinolite-chlorite schists (greenschists) and amphibolites. Eclogites—garnet-jadeite rocks—form at very great depths. When sandstones and limestones undergo metamorphism, quartzites and marble form.

Metamorphic rocks resulting from contact with intrusives (contact metamorphism) have a characteristic corneous texture. Argillaceous and other aluminosilicate rocks that undergo metamorphism become such types of hornfelses as pyroxene, biotite, and amphibolite hornfelses; limestones become marbles, and bauxites are converted to corundum rocks (emeries).

Metasomatic rocks are frequently associated with meta-morphic rocks.

A. A. MARAKUSHEV

References in periodicals archive ?
The oldest units in the area of interest are the metamorphic rocks of the McMillan Flowage Formation and the Barachois River Metamorphic Suite (Fig.
Metamorphic rocks show variable schistosity with westward dips and some local folds.
My collection was inspired by rocks -- metamorphic rocks," he said.
METAMORPHIC: Formed when heat and pressure change sedimentary, igneous, or other metamorphic rocks.
Baragiola, a professor of engineering physics in the University of Virginia School of Engineering and Applied Science set up experiments to measure ozone produced by crushing or drilling into different igneous and metamorphic rocks, including granite, basalt, gneiss, rhyolite and quartz.
One hole was drilled in 1991 to test a IP/resistivity anomaly intersected high grade metamorphic rocks with graphite.
Gold mineralization at Trun is associated with large granite and syenite stocks that intrude a broad anticline of metamorphic rocks.
The Rossing deposit contains a large steeply dipping uraniferous alaskite body, which extensively intrudes a highly folded sequence of metamorphic rocks at the contact of banded gneiss and marble units.
The void evokes the human scull but also a seed or an egg with the layering of its casing reminiscent of metamorphic rocks, seashells and the annual rings of trees.
Metamorphic rocks are found mainly as Precambrian (>570 million year) basement rocks.
Among the topics are pressure-temperature evolution and evidence for solution-mass-transfer deformation, brittle strain on the Coast Range fault zone, and the role of ductille thinning of the overburden to exhumation of the high-pressure metamorphic rocks.
Worcester and points north and west belong to the Merrimack terrane, whose bedrock is largely composed of metamorphic rocks.