Granite is given as a coarse- or medium-grained intrusive igneous rock that is rich in feldspar and quartz. It is also the most common plutonic rock of the crust of Earth, which is formed by the magma cooling (silicate melt) at depth. The other names of granite are granite igneous rock, granite constituents, and more.
Due to its use as a building stone and paving block, at one time, the quarrying of granite was a major industrial activity. However, except for the tombstones, for which there is a continuing demand, the present granite production can be geared to the fluctuating market for curbing in veneer and highway construction, which is used in the facing of commercial and large industrial buildings.
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Granite can take place in sills or dikes (which are the tabular bodies injected in the fissures and also inserted between the other rocks), but more characteristically, it produces irregular masses of extremely variable size by ranging from less than 8 km or 5 miles in maximum dimension to the larger masses (otherwise batholiths) that are often either hundreds or thousands of square km in area.
The principal constituent of the granite is given as feldspar. Both the alkali feldspar and plagioclase feldspar are usually abundant in it, and the relative abundance of them has provided the basis for granite classifications. In most of the granite, the dominant ratio to the subdominant feldspar is below or less than two. This includes the most granites from the central, eastern, and southwestern England, southwestern United States, the Fennoscandian (Baltic Shield) area, central and western France, Spain, and several other areas.
Granites, where the plagioclase greatly exceeds alkali feldspar, are common in the large regions of the western United States and are thought to be characteristic of the great batholiths series stretching from British Columbia southward and Alaska through California and Idaho into Mexico. Granites having a great excess of alkali feldspar vs. plagioclase are much very well known from New England; they take place in the smaller bodies at a number of sites in British Neogene and Paleogene rocks and in Norway's Oslo region, but their most extensive development is in northern Nigeria.
Physical Properties of Granite
The granite's average density ranges between 2.65 and 2.75 g/cm3; usually, its compressive strength lies above 200 MPa, and its viscosity falls near STP is 3–6·1020 Pa·s.
The melting temperature of the dry granite at ambient pressure is given as 1215–1260 °C; it is strongly reduced in the presence of water, down to the 650 °C at some kBar pressure.
Occurrence of Granite
Granitic rock can be widely distributed throughout the continental crust. Most of this quantity was intruded at the Precambrian age, and it is the most abundant basement rock, which underlies the continent's relatively thin sedimentary veneer. Granite's outcrops tend to form domes, Bernhardt's or tors, and also rounded massifs.
Sometimes granites occur in the circular depressions surrounded by a range of hills, which are formed by the metamorphic hornfels or aureole. Often, granite occurs as relatively small, with less than 100 km2 stock masses (which are stocks), and in the batholiths, which are often associated with the orogenic mountain ranges. At the same time, the small dikes of the granitic composition, which are called aplites, are often associated with the granitic intrusion margins. In other locations, very coarse-grained pegmatite masses take place with granite.
Origin of Granite
Granite is produced from silica-rich (it means felsic) magmas. These felsic magmas are thought to produce by the addition of water vapour or heat to the rock of the lower crust rather than by the mantle rock decompression, as is the case with the basaltic magmas. Also, it has been suggested that some of the granites found at convergent boundaries between the tectonic plates, where the oceanic crust subducts down to the continental crust, were formed from the sediments that are subducted with the oceanic plate. The melted sediments would have formed a magma intermediate in its silica content, which further became enriched in silica as it rose through the overlying crust.
Alphabet Classification System
The origin and composition of any magma that varies into the granite leave certain petrological evidence as to what the parental rock of granite was. The final composition and texture of granite are usually distinctive, the same as that of its parental rock. For example, a granite that is derived from the partial melting of the metasedimentary rocks can contain more alkali feldspar, whereas a granite that is derived from the partial melting of meta igneous rocks can be richer in plagioclase. It is based on the modern "alphabet" classification schemes.
Granitization is the largely discounted and old hypothesis that granite can be formed in place through extreme metasomatism. Fluids bring in elements, such as potassium, and remove the others, such as calcium, to transform a metamorphic rock into the granite. This should take place across a migrating front. However, by the 1960s, the experimental work had established that granites were the origin of igneous. The chemical and mineralogical features of the granite are explained only by the relations of the crystal-liquid phase, representing that there must have been at least enough melting for magma mobilization.