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 ?
Petrological investigations of zoned garnet have played a key role in obtaining information on the mineral chemistry equilibria developed during the PT evolution of metamorphic rocks, and garnet is one of the most suitable minerals since, due to its slow cation diffusion, is able to preserve shells with an original chemical composition (Ague and Carlson, 2013), often accompanied by a rapid growth after nucleation, allowing the inclusion of syn-kinematically matrix minerals (Ortolano et al.
But over time, the sedimentary rock was squeezed, heated, and transformed into a metamorphic rock called quartzite.
The Silesian domain (subdivided into the Stare Mesto belt, Velke Vrbno unit, Desna dome, and Keprnik dome regional geological units, see Figure 1) is characterized by various metamorphic rocks including orthogneiss, paragneiss, schist, amphibolite, and mylonite.
Forms when metamorphism (heat and pressure) changes sedimentary, igneous, or other metamorphic rocks.
This indicates that the granitic provenance is dominant over the metamorphic rocks, (Bokman, 1952).
The concept of a Depreciation Index, defined above, was applied to a range of soils formed on basaltic, granitic, and metamorphic rocks in humid tropical Queensland.
However, diamonds are precious mineral gems, not metamorphic rocks.
Metamorphic rocks have been modified by heat and/or pressure activity upon rocks.
The three papers in the first section focus on petrological observations combined with trace element and isotopic data of accessory minerals to link their formation with major mineral phases, and ultimately to the pressure-temperature-time path of metamorphic rocks.
Later, geologists declined from that idea and suggested that higher-grade metamorphic rocks of South Estonia, Latvia, Lithuania, and NW Belarus (the Baltic-Belarus High), usually complemented by high geophysical anomalies, can be correlated with other high-grade metamorphic complexes in East and NE Europe and thus can be considered to be of Archaean age (Puura et al.
In particular, the Bohemian Massif displays continuous areas with high-grade metamorphic rocks, including various types of migmatites (metatexites and also diatexites).
This thickening has resulted in an increase in temperature and pressure deep below the surface, which has caused the sedimentary rocks transform into crystalline metamorphic rocks.