Granulite
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Granulite is a fine to medium -grained metamorphic rock ( a metamorphic rock or metamorphic rock ) with a fine-grained, uniform structure, which is created under high pressure and high temperature. The main constituents are feldspar with quartz and garnet. It is finer-grained than granite, from which the name derives. In Germany granulite occurs in the Saxon Granulitgebirge. In Austria, for example, the Dunkelsteinerwald consists mainly of granulite.
Description
As granulite (Latin granum = grain ) is called in the broader sense any type of rock that has been metamorphosed under granulite conditions. Granulite conditions are characterized by temperatures above about 750 ° C and pressures below about 1.4 GPa (corresponding Erdkrustentiefen <45 - 50 km ). Thus granulites are formed in the lower crust.
Granulites with acidic or basic composition can be seen in the occurrence of metamorphic orthopyroxene formed. Acid granulites (SiO2 - rich ) are also referred to as Charnockite, basic granulites (SiO2 - poorer ) than Enderbit. In some rocks ( eg marble, quartzite ) is due to the simple mineral holdings recognizing granulite conditions is not always possible.
Mostly granulites show a bulky, medium - to coarse -grained texture. Occasionally, by Einregelung of quartz, biotite and / or the presence of leuco - and melanosomes (see anatexis ) a gneiss -like structure arise.
Minerals that often occur in granulites are quartz, plagioclase, garnet, alkali feldspar, biotite, sillimanite, orthopyroxene, clinopyroxene and cordierite. Very popular as exclusive natural stones are the granulites, run the stored red garnet in their mineral composition. They are also called shells gneisses.
At extremely high temperatures (> 900 ° C) and moderate pressures ( from 0.7 to 1.3 GPa) show aluminum-rich, pelitic granulites characteristic mineral assemblages ( mineral assemblages ) such as sapphirine quartz, spinel quartz and orthopyroxene sillimanite. In such cases, one speaks of ultrahigh -temperature metamorphism ( UHT metamorphism ).
There are two typical retrograde pressure-temperature trends ( PT- paths) from granulites: isobaric cooling ( IBC = isobaric cooling ) and isothermal decompression ( ITD = isothermal decompression ). Wherein the isobaric cooling Granulit without significant pressure change is cooled, which indicates heat supply by, for example, a magma intrusion. In the isothermal decompression occurs relatively rapid uplift followed by cooling. This can be explained by orogenic collapse after a Erdkrustenverdickung.
Types of natural stone
- Kashmir White ( India, Madurai )
- New Kashmir (Brazil, Minas Gerais )