Granite ( ) is a common type of felsik intrusive frozen rock that has a granular and phaneryic texture. Granite can be predominantly white, pink, or gray, depending on their mineralogy. The word "granite" comes from the Latin granum , a grain, refers to a rough structure like a holocrystalline stone. Strictly speaking, granite is a frozen rock with between 20% and 60% quartz by volume, and at least 35% of the total feldspar consisting of alkali feldspar, although generally the term "granite" is used to refer to a wider range of rough igneous rocks containing quartz and feldspar.
The term "granite" means like granite and is applied to granite and a cluster of intrusive igneous rocks with a similar texture and slight variation in composition and origin. These rocks consist mainly of feldspar minerals, quartz, mica, and amphibole, which form an interlocking, slightly equigranular feldspar and quartz matrix with dark scattered biotic mica and amphibole (often hornblende) flavoring lighter color minerals. Sometimes some individual crystals (phenocrysts) are larger than groundmass, in this case a texture known as porphyritic. A granite stone with porphyritic texture known as granite porphyry. Granitoid is a general term, descriptive field for lighter-grained colored rocks. Petrographic examination is required for the identification of certain types of granitoids. The extrusion of frozen rock equivalent of granite is rhyolite.
Granite is almost always large (has no internal structure), hard and tough, and therefore has been used extensively throughout human history as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm 3 (165.4 - 171.7 lb/ft 3 ), the compressive strength is usually above 200 MPa, and its viscosity near STP is 3-6 o 10 19 PaÃ, Â · s.
The dry granite melting temperature at ambient pressure is 1215-1260 ° C (2219-2300 ° F) ; it is greatly reduced in front of the water, up to 650 ° C at a pressure of several kBar.
Granite has poor overall permeability overall, but strong secondary permeability through cracks and fractures if present.
Video Granite
Mineralogi
Granite is classified according to QAPF diagrams for coarse-grained plutonic rocks and named after quartz percentages, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar at half A-Q-P from the diagram. The actual granite (according to modern petrological conventions) contains plagioclase and alkali feldspars. When granitoid is absent or almost without plagioclase, this stone is referred to as an alkali feldspar granite. When granitoid contains less than 10% orthoclase, it is called tonalite; pyroxene and amphibole often occur on tonalite. A granite containing muscovite and biotite muskovars is referred to as binary granite or two-mica . Two mica granules are usually high in potassium and low in plagioclase, and are usually granite type S or granite type-A.
Chemical composition
The world average of granite chemical composition, by weight percent, based on 2485 analysis:
Maps Granite
Genesis
Granite-containing rocks are widespread throughout the continental crust. Many were intruded during the age of Precambria; it is the most abundant underground rock that underlies the relatively thin layer of sediment from the continents. Granite outcrops tend to form tors and massif round. Granite sometimes occurs in circular depressions surrounded by various hills, formed by metamorphic aureole or hornfels. Granite often occurs as a relatively small stock, less than 100Ã, kmÃ, mass (shares) and in batholiths that are often associated with orogenic mountains. Small dikes of granite compositions called aplites are often associated with granite intrusion margins. In some locations, very rough pegmatite masses occur with granite.
Origin
Granite has a felsic composition and is more common in recent geologic times unlike the history of Earth's ultramafic rocks. Felsic rocks are less dense than mafic and ultramafic stones, and therefore they tend to escape from subduction, whereas basaltic or gabbroic rocks tend to sink into the mantle beneath granite rocks from the crater of the continent. Therefore, granite rocks form the basement of all continents of the land.
Geochemical origins
Granitoids have crystallized from magma having a composition at or near the eutectic point (or the minimum temperature on the cotectic curve). Magma will evolve into eutectic because of frozen differentiation, or because they represent a low rate of partial melting. Fractional crystallization serves to reduce melt in iron, magnesium, titanium, calcium and sodium, and enrich melt in potassium and silicon-alkali feldspar (rich in potassium) and quartz (SiO 2 ), are two of the constituent defining granite.
This process operates regardless of the origin of parental magma on granite, and irrespective of the chemistry. However, the composition and origin of magma that differentiate into granite leave certain geochemical and mineral evidence as to what the granite's grindstone is. Mineralogy, texture and final chemical composition of a granite are often different from their origin. For example, granite formed from melt deposits may have more alkali feldspars, whereas granite derived from liquid basalt may be richer in feldspar plagioclase. It is on this basis that the modern "alphabet" classification scheme is based. Granite has a slow cooling process that forms larger crystals.
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Chappell & amp; based mail The white classification system was originally proposed to divide granite into granite I-type granite (or igneous protolith) and S-type or sedimentary granular protolith. Both types of granite are formed by high grade metamorphic rock melting, either granite or other intrusive mafic rocks, or buried sediments respectively.
M-type or granite derived coats are then proposed to cover the granite that is clearly sourced from crystalline mafic magma, commonly sourced from the mantle. This is rare, as it is difficult to convert basal to granite by fractional crystallization.
A-type or anorogenic granite forms above the volcanic "hot spot" activity and has a unique mineralogy and geochemistry. These granites are formed by a lower melting of the skin under conditions that are usually very dry. A-type granite occurs in Koettlitz Glacier Alkaline Province in the Royal Society Range, Antarctica. Rhyolites of Yellowstone Caldera are examples of volcanic equivalents of granite type A.
H-type granules or hybrids are formed after mixing two granite magmas from various sources, eg. M-type and S-type.
Granitization
The old theory, and most of the discount, granitization states that granite is formed in place by extreme metacomatism by liquids carrying elements, eg. potassium, and eliminating others, eg. calcium, to turn metamorphic rock into granite. This should happen in front of the migrate. The production of granite by metamorphic heat is difficult, but is observed to occur in certain amphibolite and granulite fields. In-situ or melted granitization by metamorphosis is difficult to recognize except where leukosome and melanosomal textures are present in migmatites. Once a metamorphic rock melts, it is no longer a metamorphic rock and a magma, so these rocks are seen as a transition between the two, but technically not granite because they do not actually enter other rocks. In all cases, the melting of solid rock requires high temperatures, and also water or other volatile substances that act as catalysts by lowering the temperature of rock solids.
Ascent and emplacement
The climbing and placement of large volumes of granite in the upper crust of the continent is a source of debate among geologists. Lack of field evidence for each proposed mechanism, so the hypothesis is largely based on experimental data. There are two main hypotheses for climbing magma through the crust:
- Stokes diapir
- Fracture spread
Of these two mechanisms, Stokes diapir favored for years without any reasonable alternative. The basic idea is that magma will rise through the crust as a mass through buoyancy. As it rises, it heats up rock walls, causing them to behave as fluid laws of force and thus flowing around the plutons that allow it to pass quickly and without the loss of great heat. It is entirely feasible in the warmer and brittle crust of the earth where the rocks are easily deformed, but have problems in the much cooler and more fragile upper crust. Rocks are not easily deformed: for magma to rise up as a pluton, it will release too much energy in heating the rocks of the walls, thus cooling and hardening before reaching a higher level inside the crust.
Propagation fractures are the mechanism favored by many geologists as they largely eliminate the major problem of moving mass of enormous magma through the fragile cold crust. Magma rises instead of in small ducts along the self-propagating embankment formed along a new or pre-existing fracture or fault system and an active shear zone network. As this narrow channel opens, the first magma entering freezes and provides insulation for the magma later.
Magma granite must make room for itself or intruded into other rocks to form intrusion, and several mechanisms have been proposed to explain how the large batholith has been emplaced:
- Stop, where granite cracks the rocks of the wall and pushes upward as it removes blocks from the top crust
- Assimilation, where granite melts to the crust and removes the top material in this way
- Inflation, where the granite body expands under pressure and is injected into the position
Most geologists today accept that a combination of these phenomena can be used to explain granite intrusion, and that not all granites can be fully explained by one or the other mechanism.
Weathering
Physical weathering occurs on a large scale in the form of skin peeling joints, which is the result of granite expansion and fracture as the pressure is reduced when the top material is removed by erosion or other processes.
The chemical weathering of granite occurs when diluting carbonic acid, and other acids present in rainwater and soil, converts the feldspar in a process called hydrolysis. As shown in the following reaction, this causes the potassium feldspar to form kaolinite, with potassium, bicarbonate, and silica ions in solution as a by-product. The end product of granit weathering is grus, which is often made of coarse grains of disintegrated granite.
- 2 Sub <3> 3 2 H 2 CO 3 9 H 2 O -> Al 2 The 2 4 4 H 4 SiO 4 2 K 2 HCO 3 -
Climate variations also affect the level of weathering of granite. For about two thousand years, the carvings in Cleopatra's Needle obelisk have survived the arid conditions of their origin before being transferred to London. Within two hundred years, red granite has drastically worsened in the wet and polluted air there.
Natural Radiation
Granite is a natural source of radiation, like most natural stones.
Potassium-40 is a weakly emission radioactive isotope, and alkali feldspar constituents, which in turn are common components of granite rock, are more abundant in alkali feldspar granite and syenites. Of course, the geiger counter should register this low effect.
Some granites contain about 10 to 20 parts per million (ppm) of uranium. In contrast, more mafic rocks, such as tonalite, gabbro and diorite, have 1 to 5 ppm uranium, and limestone and sedimentary rocks typically have an equally low amount. Many of the large granite plutons are sources for deposition of palaeochannel or host uranium ore deposits, where uranium washes into the sediments of granite plateau and related, often radioactive pegmatites. Warehouses and basements built above ground on granite can be a trap for radon gas, formed by uranium decay. Radon gas poses significant health problems and is the second leading cause of lung cancer in the US behind smoking.
Thorium occurs in all granites as well. Conway granite has been noted for relatively high thorium concentrations of 56 Ã, Â ± 6 ppm.
There are some concerns that some granites sold as countertops or building materials can be harmful to health. And Steck of St. Johns University has stated that about 5% of all granites are of concern, with the caveat that only a fraction of the tens of thousands of granite slab types have been tested. Resources from national geological survey organizations can be accessed online to assist in assessing risk factors in granite countries and related design rules, in particular, to prevent the accumulation of radon gas in basements and closed dwellings.
A study of granite countertops was performed (initiated and paid for by the Marble Institute of America) in November 2008 by National Health and Engineering Inc. USA. In this test, all 39 measured granite measurements for the study showed radiation levels well below the EU safety standard (section 4.1.1.1 of the National Health and Engineering study) and the level of radon emissions well below the average concentration of outdoor radon in US.
Industry
Granite and related marble industries are considered as one of the oldest industries in the world; there as far as the Ancient Egyptians.
The main modern exporters of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain and USA.
Indian granite mining has been mired in controversies over child labor and slavery.
Usage
Antiquity
The Egyptian Red Pyramid (26th century BC), named after the bright red color of its open limestone surface, is Egypt's third largest pyramid. The Menkaure pyramid, probably from the same era, was built of limestone and granite blocks. The Great Pyramid of Giza (about 2580 BC) contains a large granite sarcophagus made from "Red Aswan Granite". The mostly damaged Black Pyramid from the reign of Amenemhat III once had a pyramid or granite gemstone, 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 veneer walls and floors. How the Egyptians worked on solid granite is still a matter of debate. Patrick Hunt has postulated that the Egyptians used emery, which has greater violence on the Mohs scale.
Rajaraja Chola I of the Chola Dynasty in South India built the world's first complete shrine of granite in the 11th century in Tanjore, India. The temple of Brihadeeswarar dedicated to Lord Shiva was built in 1010. The giant gopuram (ornament, the upper part of the temple) is believed to have a mass of about 81 tons. It is the tallest temple in southern India.
The granite of the Roman Empire was excavated mainly in Egypt, and also in Turkey, and on the islands of Elba and Giglio. Granite became "an integral part of the monumental Roman language architecture". Mining stopped around the third century AD. Beginning in the Ancient End, granite is reused, which, at least since the early 16th century, is known as spoliation. Through a case-hardening process, granite becomes harder as you get older. The technology needed to make hardened steel chisels was largely forgotten during the Middle Ages. As a result, medieval stonemasons were forced to use chainsaws or sandpaper to shorten the ancient columns or break them into discs. Giorgio Vasari noted in the 16th century that granite in mining was "much softer and easier to work than after it was uncovered" while the ancient columns, due to "violence and solidity they need not fear from fire or sword, and time itself, which pushes everything to spoil, not only does it destroy them but does not even change their color. "
Modern
Statues and warnings
In some areas, granite is used for tombstones and memorials. Granite is a rock hard and requires the skill to carve by hand. Until the early 18th century, in the Western world, granite can only be carved with hand tools with generally poor results.
A key breakthrough was the invention of cutlery and steam-powered clothing by Alexander MacDonald of Aberdeen, inspired by the sight of Egyptian granite carvings. In 1832, the first polished tombstone of Aberdeen granite to be erected at British cemetery was installed at Kensal Green Cemetery. This caused a sensation in the monumental trade of London and for several years all the polished granite ordered came from MacDonald. As a result of the work of sculptor William Leslie, and later Sidney Field, the granite memorial became a major status symbol in Victorian England. The royal sarcophagus at Frogmore is probably the culmination of his work, and at 30 tons one of the largest. It was not until the 1880s that competing machines and works competed with MacDonald.
Modern methods of engraving include using computer-controlled rotary bits and sandblasting through rubber stencils. Leaving letters, numbers, and emblems exposed in stone, blaster can create almost any kind of artwork or gravestone.
The stone known as "black granite" is usually gabbro, which has an entirely different chemical composition.
Building
Granite has been widely used as dimensional stone and as a floor tile in public buildings and monuments. Aberdeen in Scotland, built primarily of local granite, is known as "The Granite City". Due to its abundance in New England, granite is usually used to build the foundation for the home there. The Granite Railway, the first railroad in America, was built to transport granite from a quarry in Quincy, Massachusetts, to Neponset River in the 1820s.
Engineering
Engineers traditionally use polished granite surface plates to define reference plots, as they are relatively resistant and inflexible. Sandblasted concrete with a heavy aggregate content has a look similar to rough granite, and is often used as a substitute when the use of indigenous granite is impractical. The most unusual use of granite was as a material from the trace of the Haytor Granite Tramway, Devon, England, in 1820. Granite blocks are usually processed into slabs, which can be cut and shaped by cutting centers. The granite tables are widely used as the basis for optical instruments due to granite rigidity, high dimensional stability, and excellent vibration characteristics. In military engineering, Finland planted granite stones along its Mannerheim Line to block the invasion by Russian tanks in the winter war of 1940.
Other uses
Curling stones are traditionally made from Ailsa Craig granite. The first stone was made in the 1750s, the original source was Ailsa Craig in Scotland. Due to the scarcity of these granites, the best stones can cost up to 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 excavations under license for Ailsa granite by Kays of Mauchline for curling stones.
Rock climbing
Granite is one of the most valuable rocks by climbers, due to its steepness, health, cracking system, and friction. Notable places for granite climbing include the Yosemite Valley, Bugaboo, Massif Mont Blanc (and peaks such as Aiguille du Dru, Morne Mountains, Adamello-Presanella Alps, Aiguille du Midi and Grandes Jorasses), Bregaglia, Corsica, part of Karakoram (especially Trango Towers ), Fitzroy Massif, Patagonia, Baffin Island, Ogawayama, Cornish coast, Cairngorms, Sugarloaf Mountain in Rio de Janeiro, Brazil, and Stawamus Chief, British Columbia, Canada.
Rock climbing granite is so popular that many of the artificial cliff wall walls found in gyms and playgrounds are made to look and feel like granite.
See also
References
- Notes
Further reading
- Blasik, Miroslava; Hanika, Bogdashka, eds. (2012). Granite: Genesis, Mineralogy and Origin . Hauppauge, New York: Nova Science. ISBN: 978-1-62081-566-3.
- Twidale, Charles Rowland (2005). Landscape and Geology of Granite Terrains . Leiden, Netherlands: A. A. Balkema. ISBN: 978-0-415-36435-5.
- Marmo, Vladimir (1971). Petrology Granite and Granite Problem . Amsterdam, Netherlands: Elsevier Scientific. ISBN: 978-0-444-40852-5. <
External links
- The Emplacement and Granite Origin
Source of the article : Wikipedia
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