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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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Green and light bluish-green, hexagonal prismatic beryl crystals occur in stream sediment that transects the metamorphic units, suggesting that the chromium-rich beryl developed within the metamorphic rocks consisting of garnet, glaucophane, epidote, chlorite, feldspar, quartz, lawsonite, muscovite, augite and sphene.
For example, a drop is produced in the Lm/Rt index indicating a smaller contribution of low-grade metamorphic rocks towards the top of the sedimentary succession.
However, most of the available radiometric age data from the plutonic and metamorphic rocks record Neoproterozoic to Devonian movement, too old to correlate with the post-Windsor Group thrusting identified here.
When the LCPC test results were examined group wise the sedimentary rocks showed a moderate correlation with R2 value of 0.72; whereas very good correlation with R2 value of 0.95 existed for the combined group of igneous and metamorphic rocks. Comparison of LCPC test results illustrate that twelve rock samples showed higher ABR (g/t) values at the suggested speed of 4500 rpm which may be due to high strength of the rocks abrading the steel insert by elevated impact energy.
The SSZ consists of Paleozoic to Triassic high-grade metamorphic rocks overlaid by Mesozoic metasedimentary strata.
Sedimentary and metamorphic rocks are generally denser and lie in the paramagnetic susceptibility field and in the low Q region.
The deepwater ascent through igneous and metamorphic rocks with sulphide content, (where conditions are anoxic) can cause sulfur sources on the surface (e.g.: Spa of Guitiriz, Banos da Brea, Termas de Cuntis) .
* Using the rock cycle to describe relationships between sedimentary, igneous and metamorphic rocks and the processes that form them
New research shows that the answer may lie in a second geological curiosity - a dramatic boundary, known as the Great Unconformity, between ancient igneous and metamorphic rocks and younger sediments.
IGNEOUS ROCK: Formed when metamorphic rocks melt to form magma (melted rock), which then cools underground or erupts and cools on Earth's surface.