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Granite (/ ˈ ɡ r æ n ɪ t / GRAN-it) is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase.It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground.
Igneous rock, with gray groundmass and white phenocrysts marked. Orthoclase phenocrysts within a finer-grained matrix of a granite porphyry. The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded.
The Barberton Mountain is a well preserved pre-3.0 Ga granite-greenstone terrane. The greenstone belt consists of a sequence of mafic to ultramafic lavas and metasedimentary rocks emplaced and deposited between 3.5 and 3.2 Ga. The granitoid rocks were emplaced over a 500 million year time span and can be divided into two suites.
Igneous intrusions may form from a single magmatic event or several incremental events. Recent evidence suggests that incremental formation is more common for large intrusions. [34] [35] For example, the Palisades Sill was never a single body of magma 300 meters (980 ft) thick, but was formed from multiple injections of magma. [36]
They are recognized by a specific set of mineralogical, geochemical, textural, and isotopic characteristics that indicate, for example, magma hybridization in the deep crust. [2] I-type granites are saturated in silica but undersaturated in aluminum ; petrographic features are representative of the chemical composition of the initial magma.
Granite rock hand-sized sample. A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental crust [1].
Granophyric textures can be found in S-type granites, particularly leucocratic ones. In porphyritic S-type granites, phenocrysts are commonly feldspars, but can also be quartz, and in rare cases, such as the Strathbogie Granite, cordierite. Figure 7 shows an example of granophyric texture in the Strathbogie Granite. The mineral quartz (light ...
Granite forms deep in the Earth's crust under conditions of high ambient or lithostatic pressure. In order for the granite to be exposed at the Earth's surface a considerable thickness of rock must be eroded. This unloading allows the granite to expand radially and sheet fractures form tangentially to the radial stress. This indicates that the ...