What is a granite gneiss complex?
a holocrystalline shale rock consisting, like granite, of quartz, potash feldspar, acid plagioclase, and mica (predominantly biotite). For this reason, the name granite-gneiss is sometimes used to denote macrocrystalline gneisses that are rich in granitic material. …
How is granitic gneiss formed?
Granite Gneiss/Schist. Gneiss is a metamorphic rock formed by changing schist, granite, or volcanic rocks through intense heat and pressure. Gneiss is foliated, which means that it has layers of lighter and darker minerals. Granitic gneiss has a mineral composition similar to that of granite.
What is the composition of gneiss?
Gneiss is a medium- to coarse-grained, semischistose metamorphic rock. It is characterized by alternating light and dark bands differing in mineral composition (coarser grained than schist). The lighter bands contain mostly quartz and feldspar, the darker often contain biotite, hornblende, garnet or graphite.
How gneiss and granite are different?
In simplified terms, you can think of gneiss as a metamorphic version of granite. Both gneiss and granite are made of feldspars, quartz, mica, and smaller amounts of dark colored minerals like hornblende. The difference between granite and gneiss is in their overall texture and movement. Granite is evenly speckled.
What is biotite gneiss?
Biotite gneiss is a metamorphic rock found in Evje, Norway. These specimens exhibit alternating bands of black and white minerals, derived from quartz, plagioclase feldspar and biotite mica.
What is banded gneiss?
gneiss, metamorphic rock that has a distinct banding, which is apparent in hand specimen or on a microscopic scale. Gneiss is medium- to coarse-grained and may contain abundant quartz and feldspar, which some petrographers regard as essential components.
What are granite gneiss and greenstone complexes?
Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.
What is the subclassification of gneiss?
Gneiss (Figure 10.17) forms at the highest pressures and temperatures, and has crystals large enough to see with the unaided eye. Gneiss features minerals that have separated into bands of different colours. Figure 10.17 Gneiss, a coarse-grained, high grade metamorphic rock, is characterized by colour bands.
Where is gneiss commonly found?
Gneisses result from the metamorphism of many igneous or sedimentary rocks, and are the most common types of rocks found in Precambrian regions. Gneiss is found in New England, the Piedmont, the Adirondacks, and the Rocky Mts. Some gneisses are used as facing stone on buildings.
What environment is gneiss formed in?
How Does Gneiss Form? Gneiss usually forms by regional metamorphism at convergent plate boundaries. It is a high-grade metamorphic rock in which mineral grains recrystallized under intense heat and pressure.
How does granite change into gneiss?
Granite is an igneous rock that forms when magma cools relatively slowly underground. It is usually composed primarily of the minerals quartz, feldspar, and mica. When granite is subjected to intense heat and pressure, it changes into a metamorphic rock called gneiss.
Is gneiss a sedimentary rock?
Gneiss is a coarse to medium grained banded metamorphic rock formed from igneous or sedimentary rocks during regional metamorphism.
What is Rock Mills Granite gneiss?
Rock Mills Granite Gneiss – coarse to medium-grained biotite granite gneiss; locally includes thick bands of epidote and thin, small amphibolite bodies. Boundary between Rock Mills Granite Gneiss and Camp Hill Granite Gneiss arbitrarily defined.
What is granitic gneiss made of?
Foliated granitic gneiss (Devonian?) Foliated granitic gneiss – Light-gray, coarse-grained, strongly to weakly foliated gneiss, composed of phenocrysts of K-feldspar in a groundmass of plagioclase, quartz, K-feldspar, and biotite, with accessory sillimanite and garnet. Glastonbury Gneiss (Middle?
What is Maromas granite gneiss?
Maromas Granite Gneiss (Devonian?) Maromas Granite Gneiss – Light-gray to buff, medium- to fine-grained granitic gneiss, composed of quartz and microcline with minor plagioclase and biotite. Central body is massive, but outlying strips are foliated and have accessory hornblende or garnet.
What is Potter Hill Gneiss made of?
Potter Hill Granite Gneiss – Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet.