What is Granite?
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.
About Granite
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
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.
FAQs on Granite
1. What exactly is granite?
Granite is a type of intrusive igneous rock, which means it forms from the slow cooling of magma deep beneath the Earth's surface. It is known for its hard, crystalline structure and is primarily composed of minerals like quartz, feldspar, and mica. Its name comes from the Latin word 'granum' for grain, referring to its grainy appearance.
2. What are the main properties of granite?
Granite is well-known for several key properties that make it useful:
- Hardness: Due to its high quartz content, granite is very hard and resistant to scratching.
- Durability: It is highly resistant to weathering and pressure, making it last for a very long time.
- Crystalline Structure: It has a coarse-grained texture where you can easily see the interlocking crystals of different minerals.
- Low Porosity: Granite doesn't absorb liquids easily, which makes it resistant to staining.
3. How is granite formed?
Granite forms when molten rock, called magma, gets trapped deep within the Earth’s crust. Instead of erupting from a volcano, it cools down very slowly over thousands or millions of years. This slow cooling process allows large mineral crystals to grow, giving granite its characteristic grainy and speckled look.
4. What are the most common uses of granite in our daily lives?
Because of its strength and beauty, granite is widely used in various applications. Some common examples include kitchen countertops, floor tiles, paving stones, building facades, monuments, and gravestones. Its durability ensures that these structures and surfaces last for many decades.
5. Why does granite come in so many different colours like pink, black, and grey?
The colour of granite is determined by its mineral composition, especially the type of feldspar it contains. For example, a high concentration of potassium feldspar gives granite a pink or reddish colour. The presence of minerals like amphibole and biotite mica contributes to darker shades like black and dark grey, while quartz typically appears as light grey or white.
6. How can you tell the difference between granite and marble?
While both are used in construction, they are very different. Granite is an igneous rock with a speckled, granular appearance from visible, interlocking crystals. Marble is a metamorphic rock, often recognised by its wavy, veined patterns. A simple test is hardness: granite is much harder and will not be easily scratched by a metal knife, whereas marble is softer and can be scratched.
7. What does it mean for granite to be an 'intrusive' rock?
The term 'intrusive' refers to how the rock was formed. An intrusive igneous rock is one that solidified from magma *while still inside* the Earth's crust. It 'intruded' into the surrounding rock layers. This is different from 'extrusive' rocks, like basalt, which form from lava that erupts onto the surface and cools quickly.
8. What makes granite so strong and suitable for building materials?
Granite's incredible strength comes from two main factors. First, its mineral content, especially quartz, is inherently very hard. Second, the slow cooling process deep underground allows the mineral crystals to grow large and interlock tightly, creating a dense and robust structure that is highly resistant to both physical damage and chemical weathering.
