Granite (pronounced /ˈɡrænɨt/) is a common and widely occurring type of intrusive An intrusion is liquid rock that forms under the surface of the earth. Magma from under the surface slowly moves its way up from deep within the earth and moves into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years or more to form. As the rock slowly cools into a, felsic Felsic is a term used in geology to refer to silicate minerals, magma, 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". Felsic minerals are usually light in color and have specific gravities less than 3. Common, igneous Igneous rock is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma or lava (molten rock) cooling and becoming solid. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This rock In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids. Granites usually have a medium to coarse grained texture. Occasionally some individual crystals (phenocrysts A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock. Phenocrysts often have euhedral forms either due to early growth within a magma or by post-emplacement recrystallization) are larger than the groundmass The matrix or groundmass of rock is the fine-grained mass of material in which larger grains or crystals are embedded in which case the texture is known as porphyritic Rock microstructure includes the texture of a rock and the small scale rock structures. The words "texture" and "microstructure" are interchangeable, with the latter preferred in modern geological literature. However, texture is still acceptable because it is a useful means of identifying the origin of rocks, how they formed,. A granitic rock with a porphyritic texture is sometimes known as a porphyry 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. In its non-geologic, traditional use, the term "porphyry" refers to the purple-red form of this stone, valued for its appearance. Granites can be pink to gray in color, depending on their chemistry and mineralogy. By definition, granite has a color index (i.e. the percentage of the rock made up of dark minerals) of less than 25%. Outcrops An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.[citation needed] of granite tend to form tors A tor is a 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 Cornwall, and rounded massifs 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. The term is also used to refer to a group of mountains formed by such a structure. In mountaineering and climbing literature, a massif is. Granites sometimes occur in circular depressions 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 such as: surrounded by a range of hills, formed by the metamorphic aureole or hornfels Hornfels 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.

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 The density of a material is defined as its mass per unit volume. The symbol of density is ρ . In some countries (for instance, in the United States), density is also defined as its weight per unit volume . The density of a substance is the reciprocal of its specific volume, a representation commonly used in thermodynamics of granite is located between 2.65^[1] and 2.75 g/cm³, its compressive strength usually lies above 200 MPa and its viscosity Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. In everyday terms , viscosity is "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater at standard temperature and pressure is 3-6 • 10¹⁹ Pa·s.^[2]

The word granite comes from the Latin Latin or sometimes Roman is an Italic language originally spoken in Latium and Ancient Rome. Although often considered a dead language, in view of the fact that it has no native speakers, a small number of scholars can fluently speak it and it continues to be taught in schools and universities and has been, and currently is, used in the process of granum, a grain, in reference to the coarse-grained structure of such a crystalline A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography. The process of crystal formation via mechanisms of crystal growth is called rock.

Granitoid is used as a descriptive field term for general, light colored, coarse-grained igneous rocks for which a more specific name requires petrographic Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. Petrographic descriptions start with the field notes at the outcrop and include megascopic description of hand examination.^[3]

Mineralogy

Granite is classified according to the QAPF diagram 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 ". These are the mineral groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized (recalculated so that for coarse grained plutonic rocks A pluton in geology is an intrusive igneous rock body that crystallized from magma slowly cooling below the surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies. In practice, "pluton" usually refers to a distinctive mass of igneous rock, typically kilometers in dimension, without and is named according to the percentage of quartz Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2, alkali feldspar Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rock (orthoclase Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite, sanidine Sanidine is the high temperature form of potassium feldspar (Si,Al)4O8. Sanidine most typically occurs in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic, or microcline Microcline 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. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures than orthoclase. Sanidine is a polymorph of alkali) and plagioclase Plagioclase is an 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 series . This was first shown by the German mineralogist Johann Friedrich Christian feldspar on the A-Q-P half of the diagram. True granite according to modern petrologic Petrology is the branch of geology that studies rocks, and the conditions in which rocks form 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 Tonalite is an igneous, plutonic 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. Amphiboles and pyroxenes are common accessory minerals; pyroxene The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems. Pyroxenes have the general formula XY2O6 (where X represents calcium, sodium, iron+2 and amphibole 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 are common in tonalite. A granite containing both muscovite and biotite micas The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet- is called a binary or two-mica granite. Two-mica granites are typically high in potassium Potassium is the chemical element with the symbol K (Latin: kalium, from Arabic: القَلْيَه‎ al-qalyah "plant ashes" cf. Alkali from the same root, more commonly known in Modern Standard Arabic as بوتاسيوم ‹bwtasywm›), atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash. Elemental and low in plagioclase, and are usually S-type granites or A-type granites. The volcanic A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface equivalent of plutonic A pluton in geology is an intrusive igneous rock body that crystallized from magma slowly cooling below the surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies. In practice, "pluton" usually refers to a distinctive mass of igneous rock, typically kilometers in dimension, without granite is rhyolite This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade. Granite has poor primary permeability but strong secondary permeability.

Chemical composition

A worldwide average of the chemical composition of granite, by weight percent:^[4]

• SiO₂ The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with a chemical formula of Si — 72.04%
• Al₂O₃ Aluminium oxide is the family of inorganic compounds with the chemical formula Al2O3. It is an amphoteric oxide and is commonly referred to as alumina, corundum as well as many other names, reflecting its widespread occurrence in nature and industry. Its most significant use is in the production of aluminium metal, although it is also used as an — 14.42%
• K₂O Potassium oxide is a compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive species. Some materials of commerce, such as fertilizers and cements, are assayed assuming the percent composition that would be equivalent to K2O — 4.12%
• Na₂O Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses. Treatment with water affords sodium hydroxide — 3.69%
• CaO Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature — 1.82%
• FeO Iron oxide, also known as ferrous oxide, iron oxide/oxidized iron or more commonly rusted iron, is one of the iron oxides. It is a black-colored powder with the chemical formula Fe — 1.68%
• Fe₂O₃ Iron oxide is the inorganic compound with the formula Fe2O3. It is of one of the three main oxides of iron, the other two being FeO, which is rare, and Fe3O4, which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of the iron for the steel industry. Fe2O3 is paramagnetic, reddish brown, and — 1.22%
• MgO Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of Mg — 0.71%
• TiO₂ Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula Ti — 0.30%
• P₂O₅ Phosphorus pentoxide is a chemical compound with molecular formula P4O10. This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant — 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 The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in contrast to the oceanic crust, called sima due to its. Granite often occurs as relatively small, less than 100 km² stock masses (stocks) and in batholiths A batholith is a large emplacement of igneous intrusive (also called plutonic) rock that forms from cooled magma deep in the earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock-types, such as granite, quartz monzonite, or diorite (see also granite dome) that are often associated with orogenic Orogeny refers to forces and events leading to a severe structural deformation of the earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts. The word "orogeny" comes from the Greek , and it is the primary 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.

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 and include French, British, and American systems.

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 mineral 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.

Chappell & White classification system

The letter-based Chappell & White classification system was proposed initially to divide granites into I-type granite (or igneous protolith) granite and S-type or sedimentary protolith granite.^[5] 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 crystallized 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 rhyolites of the Yellowstone caldera are examples of volcanic equivalents of A-type granite.^[6][7]

Granitization

An old, and largely discounted theory, granitization states that granite is formed in place by extreme metasomatism by fluids bringing in elements e.g. potassium and removing others e.g. calcium to transform the metamorphic rock into a granite. This was supposed to occur across a migrating front. 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.

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