What are the 2 Protoliths of gneiss?
The protolith of gneiss may be an igneous rock, in this case it is called an orthogneiss. It forms probably because of shear in vicous granitic magma. Paragneiss is a variety with a sedimentary protolith. Even in the latter case, gneissic banding has nothing to do with original layering of sedimentary rocks.
What are the different types of gneiss?
Gneiss can be classified on the basis of minerals that are present, presumed formational processes, chemical composition, or probable parent material. Orthogneiss is formed by the metamorphism of igneous rocks; paragneiss results from the metamorphism of sedimentary rocks.
What are the 6 minerals in gneiss?
The most common minerals in gneiss are quartz, potassium feldspar, and sodium feldspar. Smaller amounts of muscovite, biotite and hornblende are common. Gneiss can also form from gabbro or shale.
What type of rock is an augen gneiss quizlet?
Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of granite, or sedimentary rock.
How is augen gneiss formed?
Augen gneiss, from the German: Augen [ˈaʊɡən], meaning “eyes”, is a gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear-bound grains (porphyroclasts), normally feldspar, surrounded by finer grained material.
What is protolith?
The original rock that has undergone metamorphism is called the protolith. Protolith can be any type of rock and sometimes the changes in texture and mineralogy are so dramatic that is difficult to distinguish what the protolith was. Note that diagenesis and weathering are also a changes in form that occur in rocks.
What is the parent rock of gneiss?
Gneiss is a medium- to coarse-grained rock formed under high grade-metamorphic conditions. Gneiss is primarily composed of quartz, potassium feldspar, and plagioclase feldspar with lesser amounts of biotite, muscovite, and amphibole. Granites and sometimes rhyolite provide the parent rock for gneiss.
What are the parent rocks of gneiss?
Which type of rock is a foliated metamorphic rock?
Foliated Metamorphic Rocks Foliated rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in. Types of foliated metamoprhic rocks include slate, schist, and gneiss.
Which type of rock is non foliated metamorphic rock?
Nonfoliated metamorphic rocks lack foliated texture because they often lack platy minerals such as micas. They commonly result from contact or regional metamorphism. Examples include marble, quartzite, greenstone, hornfel, and anthracite.
What is Augen structure?
Augen (from German “eyes”) are large, lenticular eye-shaped mineral grains or mineral aggregates visible in some foliated metamorphic rocks. In cross section they have the shape of an eye.
What does the word Augen mean?
[ ou′gən ] A large mineral grain or grain cluster having the shape of an eye in cross-section and occurring in foliated metamorphic rocks such as schist and gneiss. Augens form when large mineral crystals are sheared and deformed during the process of metamorphism.
What is a Phenocrysts in geology?
A relatively large crystal embedded in a finer-grained or glassy igneous rock. The presence of phenocrysts gives the rock a porphyritic texture (see illustration). Phenocrysts are represented most commonly by feldspar, quartz, biotite, hornblende, pyroxene and olivine.
What rock is metamorphosed to gneiss?
Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of granite, or sedimentary rock. Gneiss displays distinct foliation, representing alternating layers composed of different minerals.
Is gneiss foliated or Nonfoliated?
Gneiss, a foliated metamorphic rock. Quartzite, a non-foliated metamorphic rock.
What does augen gneiss mean?
eyes
Augen gneiss, from the German: Augen [ˈaʊɡən], meaning “eyes”, is a gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear-bound grains (porphyroclasts), normally feldspar, surrounded by finer grained material.
What’s the difference between xenolith and Xenocryst?
Xenocrysts are a type of xenolith—one type of rock trapped in another type of rock. Here, the crystal pyroxene is trapped in the volcanic kimberlite. A xenolith is a piece of rock trapped in another type of rock. Most of the time, a xenolith is a rock embedded in magma while the magma was cooling.
What is cognate xenolith?
Cognate xenoliths Others are fragments of the lower crust or mantle and represent the original material from which magmatic liquids may be derived by partial melting. Still others are composed of crystals precipitated from a cooling magma or residual crystals left after partial melting and extraction of a liquid.
What type of metamorphic rock is augen gneiss?
augen-gneiss A medium- to coarse-grained, banded, regional metamorphic rock composed mainly of quartz and feldspar with hornblende and mica also present in variable quantities, and characterized by large ovoidal megacrysts of feldspar known as ‘augens’ (derived from the German for ‘eyes’).
Why is it called Auger gneiss?
This type of gneiss gains its name from the elliptic or lens-shaped form of many of its mineral grains. Indeed, the word augen is German for “eye,” a reference to the appearance of these readily visible components of metamorphic rocks.
What is another name for gneisses?
Gneisses which can be metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, and so on. Rhey can also be named after a characteristic component inclusive of garnet gneiss, biotite gneiss, albite gneiss, and many others.
What minerals are in augen gneiss?
Augen Gneiss. Nevertheless, generally the rock contains relatively large amounts of feldspar and quartz, as well as mica or some other dark, rock-forming mineral. The bands of the rock, which is formed via high-grade regional metamorphism, may be nearly parallel to the ground or steeply angled.