Thursday, 19 March 2015

Granite



What is granite?

Granite is an intrusive igneous coarse grained rock. Granite is formed from the very slow cooling of the magma which provided sufficient time for the crystal to grow, large enough to be seen with an unaided eye. Granite consists of mainly quartz and feldspar with minor amount of mica, amphibole and other minerals. This mineral composition results in granite colours of red, pink, white and grey with dark minerals visible.

Granite is the most common igneous rock occurring on the Earth's surface so is readily distinguishable of the other igneous rocks. Granite is also used in different forms which can be seen in a daily life things.

Granite word usage

Granite in a geology course is used for igneous rock that is light in colour and composed mainly of feldspar and quartz. In petrography it is used for a rock in which quartz is 10 to 50 percent of felsic component and alkali feldspar account for 65 to 90 percent of total feldspar content.

Mineralogy of granite

Stone is ordered by the QAPF diagram for coarse grained plutonic shakes and is named by the rate of quartz, salt feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar on the A-Q-P half of the graph. Genuine rock as indicated by current petrologic tradition contains both plagioclase and salt feldspars. At the point when a granitoid is empty or about without plagioclase, the stone is alluded to as soluble base feldspar rock. At the point when a granitoid contains under 10% orthoclase, it is called tonalite; pyroxene and amphibole are regular in tonalite. A stone containing both muscovite and biotite micas is known as a twofold or two-mica rock. Two-mica rocks are commonly high in potassium and low in plagioclase, and are generally S-sort stones or A-sort stones.

Occurrence of granite

Outcrops of granite tend to shape tors and adjusted massifs. Granite some of the time happen in roundabout encompassed by a scope of slopes, framed by the transformative aureole or hornfels. Granite is normally found in the mainland plates of the Earth's outside layer. 
Granite is at present known to exist just on Earth, where it shapes a noteworthy part of the mainland outside. Granite regularly happens as generally little, under 100 km² stock masses (stocks) and in batholiths that are frequently connected with orogenic mountain ranges. Little dams of granitic sythesis called aplites are regularly connected with the edges of granitic interruptions. In a few areas, extremely coarse-grained pegmatite masses happen with stone. 
Granite has been interfered into the covering of the Earth amid every geologic period, albeit a lot of it is of Precambrian age. Granitic shake is generally circulated all through the mainland outside and is the most plenteous storm cellar shake that underlies the moderately thin sedimentary finish of the landmasses.

Origin of granite

Granite has a felsic sythesis and is more normal in late geologic time rather than Earth's ultramafic antiquated molten history. Felsic rocks are less thick than mafic and ultramafic rocks, and along these lines they tend to escape subduction, while basaltic or gabbroic rocks tend to sink into the mantle underneath the granitic rocks of the mainland cratons. Thus, granitic rocks form the basement of all land landmasses.

Granite in Earth's crust

Granite is abundant in the Earth's crust found at many mountain ranges in their cores known as batholiths. The granite grains are larger which hence proved that it has been grown of magma slow cooling in a long period of time. These are exposed at the surface by the uplifting process as they grow deeper in the crust, no other way would have been present at surface. 
Granite when not exposed on the surface and is covered by sedimentary rocks doesn't mean they aren't there. They are present beneath the sedimentary cover as deeper crust have magma chambers which rise from mantle. So these hard rocks makes the basement rocks of the crust, hard enough to endure the sedimentary rocks overburden.

Uses of granite

Granite is used as a dimension stone, its properties of hard rock makes it well suitable for the job. These are resistive to abrasion, strong enough to endure the weight,inert to the weathering and it can be polished.

Antiquity

The Red Pyramid of Egypt (c.26th century BC), named for the light crimson hue of its exposed limestone surfaces, is the third largest of Egyptian pyramids. Menkaure's Pyramid, likely dating to the same era, was constructed of limestone and granite blocks. The Great Pyramid of Giza (c.2580 BC) contains a huge granite sarcophagus fashioned of "Red Aswan Granite". The mostly ruined Black Pyramid dating from the reign of Amenemhat III once had a polished granite pyramidion or capstone, now on display in the main hall of the Egyptian Museum in Cairo (see Dahshur). Other uses in Ancient Egypt include columns, door lintels, sills, jambs, and wall and floor veneer. How the Egyptians worked the solid granite is still a matter of debate. Dr. Patrick Hunt has postulated that the Egyptians used emery shown to have higher hardness on the Mohs scale.
Rajaraja Chola I of the Chola Dynasty in South India built the world's first temple entirely of granite in the 11th century AD in Tanjore, India. The Brihadeeswarar Temple dedicated to Lord Shiva was built in 1010. The massive Gopuram (ornate, upper section of shrine) is believed to have a mass of around 81 tonnes. It was the tallest temple in south India.

Sculpture and memorials

In some areas, granite is used for gravestones and memorials. Granite is a hard stone and requires skill to carve by hand. Until the early 18th century, in the Western world, granite could only be carved by hand tools with generally poor results.
A key breakthrough was the invention of steam-powered cutting and dressing tools by Alexander MacDonald of Aberdeen, inspired by seeing ancient Egyptian granite carvings. In 1832, the first polished tombstone of Aberdeen granite to be erected in an English cemetery was installed at Kensal Green Cemetery. It caused a sensation in the London monumental trade and for some years all polished granite ordered came from MacDonalds. Working with the sculptor William Leslie, and later Sidney Field, granite memorials became a major status symbol in Victorian Britain. The royal sarcophagus at Frogmore was probably the pinnacle of its work, and at 30 tons one of the largest. It was not until the 1880s that rival machinery and works could compete with the MacDonald works.
Modern methods of carving include using computer-controlled rotary bits and sandblasting over a rubber stencil. Leaving the letters, numbers and emblems exposed on the stone, the blaster can create virtually any kind of artwork or epitaph.
The rock known as "black granite" is usually gabbro, which has a completely different chemical composition.

Buildings

Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. Aberdeen in Scotland, which is constructed principally from local granite, is known as "The Granite City". Because of its abundance, granite was commonly used to build foundations for homes in New England. The Granite Railway, America's first railroad, was built to haul granite from the quarries in Quincy, Massachusetts, to the Neponset River in the 1820s. With increasing amounts of acid rain in parts of the world, granite has begun to supplant marble as a monument material, since it is much more durable. Polished granite is also a popular choice for kitchen countertops due to its high durability and aesthetic qualities. In building and for countertops, the term "granite" is often applied to all igneous rocks with large crystals, and not specifically to those with a granitic composition.

Engineering


Engineers have traditionally used polished granite surface plates to establish a plane of reference, since they are relatively impervious and inflexible. Sandblasted concrete with a heavy aggregate content has an appearance similar to rough granite, and is often used as a substitute when use of real granite is impractical. A most unusual use of granite was in the construction of the rails for the Haytor Granite Tramway, Devon, England, in 1820. Granite block is usually processed into slabs and after can be cut and shaped by a cutting center. Granite tables are used extensively as a base for optical instruments due to granite's rigidity, high dimensional stability and excellent vibration characteristics. In military engineering Finland planted granite boulders along its Mannerheim Line to block invasion by Russian tanks in the winter war of 1940.

Other uses

Curling stones are traditionally fashioned of Ailsa Craig granite. The first stones were made in the 1750s, the original source being Ailsa Craig in Scotland. Because of the particular rarity of the granite, the best stones can cost as much as US$1,500. Between 60 and 70 percent of the stones used today are made from Ailsa Craig granite, although the island is now a wildlife reserve and is still used for quarrying under license for Ailsa granite by Kays of Mauchline for curling stones.

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