Information about Granite

Granite (IPA: /ˈɡrænɪt/) is a common and widely occurring type of intrusive, felsic, igneous rock. Granites are usually medium to coarsely crystalline, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Outcrops of granite tend to form tors, and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.

Granite is nearly always massive (lacking internal structures), hard and tough, and therefore it has gained widespread use as a construction stone. The average density of granite is 2.75 gcm⁻³ with a range of 1.74 gcm⁻³ to 2.80 gcm⁻³. The word granite comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a crystalline rock.

Mineralogy

Granite is classified according to the QAPF diagram for coarse grained plutonic rocks (granitoids) and is named according to the percentage of quartz, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar on the A-Q-P half of the diagram. Granite-like rocks which are silica-undersaturated may have a feldspathoid such as nepheline, and are classified on the A-F-P half of the diagram.

True granite according to modern petrologic convention contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase the rock is referred to as alkali granite. When a granitoid contains <10% orthoclase it is called tonalite; pyroxene and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites. The volcanic equivalent of plutonic granite is rhyolite.

Chemical composition

A worldwide average of the average proportion of the different chemical components in granites, in descending order by weight percent, is:^[1]

• SiO₂ — 72.04%
• Al₂O₃ — 14.42%
• K₂O — 4.12%
• Na₂O — 3.69%
• CaO — 1.82%
• FeO — 1.68%
• Fe₂O₃ — 1.22%
• MgO — 0.71%
• TiO₂ — 0.30%
• P₂O₅ — 0.12%
• MnO — 0.05%
• Based on 2485 analyses

Occurrence

Granite is currently known only on Earth where it forms a major part of continental crust. Granite often occurs as relatively small, less than 100 km² stock masses (stocks) and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions. In some locations very coarse-grained pegmatite masses occur with granite.

Granite has been intruded into the crust of the Earth during all geologic periods, although much of it is of Precambrian age. Granitic rock is widely distributed throughout the continental crust of the Earth and is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents.

Despite being fairly common throughout the world, the areas with the most commercial granite quarries are located in Finland, Norway and Sweden (Bohuslän), Spain (mostly Galicia and Extremadura), Brazil, India and several countries in southern Africa, namely Angola, Namibia, Zimbabwe and South Africa.

Origin

Granite is an igneous rock and is formed from magma. Granitic magma has many potential origins but it must intrude other rocks. Most granite intrusions are emplaced at depth within the crust, usually greater than 1.5 kilometres and up to 50 km depth within thick continental crust. The origin of granite is contentious and has led to varied schemes of classification. Classification schemes are regional; there is a French scheme, a British scheme and an American scheme. This confusion arises because the classification schemes define granite by different means. Generally the 'alphabet-soup' classification is used because it classifies based on genesis or origin of the magma.

Geochemical origins

Granitoids are a ubiquitous component of the crust. They have crystallized from magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve). Magmas will evolve to the eutectic because of igneous differentiation, or because they represent low degrees of partial melting. Fractional crystallisation serves to reduce a melt in iron, magnesium, titanium, calcium and sodium, and enrich the melt in potassium and silicon - alkali feldspar (rich in potassium) and quartz (SiO₂), are two of the defining constituents of granite.

This process operates regardless of the origin of the parental magma to the granite, and regardless of its chemistry. However, the composition and origin of the magma which differentiates into granite, leaves certain geochemical and mineralogical evidence as to what the granite's parental rock was. The final mineralogy, texture and chemical composition of a granite is often distinctive as to its origin. For instance, a granite which is formed from melted sediments may have more alkali feldspar, whereas a granite derived from melted basalt may be richer in plagioclase feldspar. It is on this basis that the modern "alphabet" classification schemes are based.

Alphabet Soup Classification

The 'alphabet soup' scheme of Chappell & White was proposed initially to divide granites into I-type granite (or igneous protolith) granite and S-type or sedimentary protolith granite^[2]. Both of these types of granite are formed by melting of high grade metamorphic rocks, either other granite or intrusive mafic rocks, or buried sediment, respectively.

M-type or mantle derived granite was proposed later, to cover those granites which were clearly sourced from crystallised mafic magmas, generally sourced from the mantle. These are rare, because it is difficult to turn basalt into granite via fractional crystallisation.

A-type or anorogenic granites are formed above volcanic "hot spot" activity and have peculiar mineralogy and geochemistry. These granites are formed by melting of the lower crust under conditions that are usually extremely dry. The granite of Yellowstone caldera is an example of an A-type granite.

Granitization

An old, and largely discounted theory, granitization states that granite is formed in place by extreme metamorphism. The production of granite by metamorphic heat is difficult, but is observed to occur in certain amphibolite and granulite terrains. In-situ granitisation or melting by metamorphism is difficult to recognise except where leucosome and melanosome textures are present in gneisses. Once a metamorphic rock is melted it is no longer a metamorphic rock and is a magma, so these rocks are seen as a transitional between the two, but are not technically granite as they do not actually intrude into other rocks. In all cases, melting of solid rock requires high temperature, and also water or other volatiles which act as a catalyst by lowering the solidus temperature of the rock.

Ascent and emplacement

The ascent and emplacement of large volumes of granite within the upper continental crust is a source of much debate amongst geologists. There is a lack of field evidence for any proposed mechanisms, so hypotheses are predominantly based upon experimental data. There are two major hypotheses for the ascent of magma through the crust:

• Stokes Diapir
• Fracture Propagation

Of these two mechanisms, Stokes diapir was favoured for many years in the absence of a reasonable alternative. The basic idea is that magma will rise through the crust as a single mass through buoyancy. As it rises it heats the wall rocks, causing them to behave as a power-law fluid and thus flow around the pluton allowing it to pass rapidly and without major heat loss (Weinberg, 1994). This is entirely feasible in the warm, ductile lower crust where rocks are easily deformed, but runs into problems in the upper crust which is far colder and more brittle. Rocks there do not deform so easily: for magma to rise as a pluton it would expend far too much energy in heating wall rocks, thus cooling and solidifying before reaching higher levels within the crust. Nowadays fracture propagation is the mechanism preferred by many geologists as it largely eliminates the major problems of moving a huge mass of magma through cold brittle crust. Magma rises instead in small channels along self-propagating dykes which form along new or pre-existing fault systems and networks of active shear zones (Clemens, 1997). As these narrow conduits open, the first magma to enter solidifies and provides a form of insulation for later magma. Granitic magma must make room for itself or be intruded into other rocks in order to form an intrusion, and several mechanisms have been proposed to explain how large batholiths have been emplaced:

• Stoping, where the granite cracks the wall rocks and pushes upwards as it removes blocks of the overlying crust
• Assimilation, where the granite melts its way up into the crust and removes overlying material in this way
• Inflation, where the granite body inflates under pressure and is injected into position

Most geologists today accept that a combination of these phenomena can be used to explain granite intrusions, and that not all granites can be explained by one or another mechanism.

Natural Radiation

Granite is a normal, geological, source of radiation in the natural environment. Granite contains around 10 to 20 parts per million of uranium. By contrast, more mafic rocks such as tonalite, gabbro or diorite have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts.

Many large granite plutons are the sources for palaeochannel-hosted or roll front uranium ore deposits, where the uranium washes into the sediments from the granite uplands and associated, often highly radioactive, pegmatites.

In buildings constructed primarily from natural granite, it is possible to be exposed to approximately 200 mrems per year.^[3]

Granite could be considered a potential natural radiological hazard as, for instance, villages located over granite may be susceptible to higher doses of radiation than other communites.^[4] Cellars and basements sunk into soils formed over or from particularly uraniferous granites can become a trap for radon gas, which is heavier than air.

However, in the majority of cases, although granite is a significant source of natural radiation as compared to other rocks it is not often an acute health threat or significant risk factor. Various resources from national geological survey organisations are accessible online to assist in assessing the risk factors in granite country and design rules relating, in particular, to preventing accumulation of radon gas in enclosed basements and dwellings.

Uses

Antiquity

The Red Pyramid of Egypt (c.26th century BC), named for the light crimson hue of its exposed granite 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, [1] 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 [2] has postulated that the Egyptians used emery shown to have higher hardness on the Mohs scale.

Many large Hindu temples in southern India, particularly those built by the 11th century king Rajaraja Chola I, were made of granite. There is a large amount of granite in these structures. They are comparable to the Great Pyramid of Giza. [3]

Modern

Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. 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.

Azul Noce (Spain)

Santa Cecelia(Brazil)

Gran Violet (Brazil)

Lavanda Blue (Brazil)

</center>

Engineers have traditionally used polished granite surfaces 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. 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 $1500 (USD). Between 60–70 percent of the stones used today are made from Ailsa Craig granite, although the island is now a wildlife reserve and is no longer used for quarrying.[4]

Rock climbing

The granite peaks of the Towers of Paine in Chile

Granite is one of the rocks most prized by climbers, for its steepness, soundness, crack systems, and friction. Well-known venues for granite climbing include Yosemite, the Bugaboos, the Mont Blanc massif (and peaks such as the Aiguille du Dru, the Aiguille du Midi and the Grandes Jorasses), the Bregaglia, Corsica, parts of the Karakoram, the Towers of Paine, Baffin Island, the Cornish coast and the Cairngorms.

Granite rock climbing is so popular that many of the artificial rock climbing walls found in gyms and theme parks are made to look and feel like granite. Most, however, are made from manufactured materials, given the fact that granite is generally too heavy for portable rock climbing walls, as well as the buildings in which stationary walls are located.

See also

• List of minerals
• List of rock types
• Igneous rocks
• Dimension stone
• Skarn
• Greisen
• Aplite
• Batholith
• New Hampshire, the "Granite State"
• Barre (town), Vermont "Granite Capital of the World", home of the Rock of Ages Corporation
• Elberton, Georgia, the "Granite Capital of the World"
• Aberdeen, Scotland's third largest city nicknamed "The Granite City"

References

1. ^ Harvey Blatt and Robert J. Tracy (1996). Petrology, 2nd edition, New York: Freeman, 66. 
2. ^ Chappell, B.W. and White, A.J.R., 2001. Two contrasting granite types: 25 years later. Australian Journal of Earth Sciences v.48, p.489-499.
3. ^ Lehigh University
4. ^ Radiation and Life

External links

• The Emplacement and Origin of Granite

Granite may refer to:

• Granite, a type of hard rock

Vessels

• Granit Oscar class submarine, an attack/guided missile submarine, known also as Project 949
• P-700 Granit guided anti-ship missile, known also as SS-N-19 Shipwreck

..... Click the link for more information.

International Phonetic Alphabet

Note: This page may contain IPA phonetic symbols in Unicode.

The International
Phonetic Alphabet
History
Nonstandard symbols
Extended IPA
Naming conventions
IPA for English The
..... Click the link for more information.

intrusion is a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto, the Roman god of the underworld.
..... Click the link for more information.

Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. The term combines the words "feldspar" and "silica.
..... Click the link for more information.

Igneous rocks (etymology from latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
..... Click the link for more information.

Balanced Rock stands in Garden of the Gods park in Colorado Springs, CO]] A rock is a naturally occurring aggregate of minerals and/or mineraloids. The Earth's lithosphere is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic.
..... Click the link for more information.

Porphyry is a variety of igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. The larger crystals are called phenocrysts.
..... Click the link for more information.

Outcrop is a geological term referring to the appearance of bedrock or superficial deposits exposed at the surface of the Earth. In most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely.
..... Click the link for more information.

tor is a type of rock outcrop formed by weathering, usually found on or near the summit of a hill. In the South West of England, where the term originated, it is also a word used for the hills themselves – particularly the high points of Dartmoor in Devon and Bodmin Moor in
..... Click the link for more information.

In geology, a massif is a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole.
..... Click the link for more information.

Depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms.

• A basin may be any large sediment filled depression.

..... Click the link for more information.

Hornfels (German, meaning "hornstone") is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable.
..... Click the link for more information.

In physics, density is mass m per unit volume V—how heavy something is compared to its size. A small, heavy object, such as a rock or a lump of lead, is denser than a lighter object of the same size or a larger object of the same weight, such as pieces of
..... Click the link for more information.

Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
..... Click the link for more information.

CRYSTAL is a quantum chemistry ab initio program, designed primarily for calculations on crystals (3 dimensions), slabs (2 dimensions) and polymers (1 dimension) using translational symmetry, but it can be used for single molecules.^[1] It is written by V.R. Saunders, R.
..... Click the link for more information.

A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogic composition. The acronym, QAPF, stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)". These are the mineral groups used for classification in QAPF diagram.
..... Click the link for more information.

A pluton in geology is an intrusive igneous rock body that crystallized from a magma below the surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies.
..... Click the link for more information.

Quartz (from German Quarz   (help info ) ^[1]) is the second most common mineral in the Earth's continental crust, feldspar being the first.
..... Click the link for more information.

Feldspar is the name of a group of rock-forming minerals which make up as much as 60% of the Earth's crust.^[1]

Feldspars crystallize from magma in both intrusive and extrusive rocks, and they can also occur as compact minerals, as veins, and are also present in
..... Click the link for more information.

Orthoclase (endmember formula KAlSi₃O₈) is an important tectosilicate mineral, which forms igneous rock. It is also known as alkali feldspar and is common in granite and related rocks.
..... Click the link for more information.

Sanidine is the high temperature form of potassium feldspar (K,Na)(Si,Al)₄O₈.^[1] Sanidine most typically occurs in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system.
..... Click the link for more information.

Microcline (KAlSi₃O₈) is an important igneous rock forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites.
..... Click the link for more information.

Plagioclase is a very important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar
..... Click the link for more information.

Normative mineralogy is a geochemical calculation of the whole rock geochemistry of a rock sample which estimates the idealised mineralogy of a rock according to the principles of geochemistry.
..... Click the link for more information.

The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks.
..... Click the link for more information.

Nepheline, also called nephelite (from Greek: nephos, "cloud"), is a feldspathoid: a silica-undersaturated aluminosilicate, Na₃KAl₄Si₄O₁₆
..... Click the link for more information.

Lithological redirects here.

Petrology (from Greek: πέτρα, petra, rock; and λόγος, logos
..... Click the link for more information.

Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less alkali feldspar. Quartz is present as more than 20% of the rock.
..... Click the link for more information.

The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rocks. They share a common structure comprised of single chains of silica tetrahedra and they crystalise in the monoclinic and orthorhombic system.
..... Click the link for more information.

Amphibole defines an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain SiO₄ tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.
..... Click the link for more information.