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|Potassium feldspar, plagioclase feldspar, and quartz; differing amounts of muscovite, biotite, and hornblende-type amphiboles|
Granite ( // ) is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. The word "granite" comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Strictly speaking, granite is an igneous rock with between 20% and 60% quartz by volume, and at least 35% of the total feldspar consisting of alkali feldspar, although commonly the term "granite" is used to refer to a wider range of coarse-grained igneous rocks containing quartz and feldspar.
In geology, felsic refers to igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava.
Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, batholiths, dikes, sills, laccoliths, and volcanic necks.
Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses. Igneous rocks occur in a wide range of geological settings: shields, platforms, orogens, basins, large igneous provinces, extended crust and oceanic crust.
The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin. These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals. Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids.The extrusive igneous rock equivalent of granite is rhyolite.
Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight.
Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.
Granite is nearly always massive (i.e., lacking any internal structures), hard, and tough. These properties have made granite a widespread construction stone throughout human history. The average density of granite is between 2.65 and 2.75 g/cm3 (165 and 172 lb/cu ft), its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6·1019 Pa·s.
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:
Compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size, as opposed to tensile strength, which withstands loads tending to elongate. In other words, compressive strength resists compression, whereas tensile strength resists tension. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
The melting temperature of dry granite at ambient pressure is 1215–1260 °C (2219–2300 °F); it is strongly reduced in the presence of water, down to 650 °C at a few kBar pressure.
Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present.
Permeability in fluid mechanics and the earth sciences is a measure of the ability of a porous material to allow fluids to pass through it.
Granite is classified according to the QAPF diagram for coarse grained plutonic rocks 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. 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 feldspar granite. When a granitoid contains less than 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.
A QAPF diagram is a double ternary 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. Q, A, P and F percentages are normalized.
In geology, a pluton is a body of intrusive igneous rock that is crystallized from magma slowly cooling below the surface of the Earth. While pluton is a general term to describe an intrusive igneous body, there has been some confusion around the world as to what is the definition of a pluton. Pluton has been used to describe any non-tabular intrusive body, and batholith has been used to describe systems of plutons. In other literature, batholith and pluton have been used interchangeably. In central Europe, smaller bodies are described as batholiths and larger bodies as plutons. In practice the term pluton most often means a non-tabular igneous intrusive body. The most common rock types in plutons are granite, granodiorite, tonalite, monzonite, and quartz diorite. Generally light colored, coarse-grained plutons of these compositions are referred to as granitoids. Examples of plutons include Denali in Alaska; Cuillin in Skye, Scotland; Cardinal Peak in Washington State; Mount Kinabalu in Malaysia; and Stone Mountain in the US state of Georgia.
Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar. The gem known as moonstone (see below) is largely composed of orthoclase.
A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses:
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Granite containing rock is widely distributed throughout the continental crust. 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.Much of it was intruded during the Precambrian age; it is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents. 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 often occurs as relatively small, less than 100
Granite has a felsic composition and is more common in continental crust than in oceanic crust. They are crystallized from felsic melts which are less dense than mafic rocks and thus tend to ascend toward the surface. In contrast, mafic rocks, either basalts or gabbros, once metamorphosed at eclogite facies, tend to sink into the mantle beneath the Moho.
Granitoids have crystallized from felsic magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve). Magmas are composed of melts and minerals in variable abundances. Traditionally, magmatic minerals are crystallized from the melts that have completely separated from their parental rocks and thus are highly evolved because of igneous differentiation. If a granite has a slowly cooling process, it has the potential to form larger crystals.
There are also peritectic and residual minerals in granitic magmas. Peritectic minerals are generated through peritectic reactions, whereas residual minerals are inherited from parental rocks. In either case, magmas will evolve to the eutectic for crystallization upon cooling. Anatectic melts are also produced by peritectic reactions, but they are much less evolved than magmatic melts because they have not separated from their parental rocks. Nevertheless, the composition of anatectic melts may change toward the magmatic melts through high-degree fractional crystallization.
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 parental magmas to granites, and regardless of their chemistry.
The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite's parental rock was. The final texture and composition of a granite are generally distinctive as to its parental rock. For instance, a granite that is derived from partial melting of metasedimentary rocks may have more alkali feldspar, whereas a granite derived from partial melting of metaigneous rocks may be richer in plagioclase. It is on this basis that the modern "alphabet" classification schemes are based.
The letter-based Chappell & White classification system was proposed initially to divide granites into I-type (igneous source) granite and S-type (sedimentary sources).Both types are produced by partial melting of crustal rocks, either metaigneous rocks or metasedimentary rocks.
M-type granite was later proposed to cover those granites that were clearly sourced from crystallized mafic magmas, generally sourced from the mantle. However, this proposal has been rejected by studies of experimental petrology, which demonstrate that partial melting of mantle peridotite cannot produce granitic melts in any case. Although the fractional crystallisation of basaltic melts can yield small amounts of granites, such granites must occur together with large amounts of basaltic rocks.
A-type granites were defined as to occur in anorogenic setting, have alkaline and anhydrous compositions. They show a peculiar mineralogy and geochemistry, with particularly high silicon and potassium at the expense of calcium and magnesium.These granites are produced by partial melting of refractory lithology such as granulites in the lower continental crust at high thermal gradients. This leads to significant extraction of hydrous felsic melts from granulite-facies resitites. A-type granites occur in the Koettlitz Glacier Alkaline Province in the Royal Society Range, Antarctica. The rhyolites of the Yellowstone Caldera are examples of volcanic equivalents of A-type granite.
H-type granites were suggested for hybrid granites, which were hypothesized to form by mixing between mafic and felsic from different sources, e.g. M-type and S-type. However, the big difference in rheology between mafic and felsic magmas makes this process hardly happening in nature.
An old, and largely discounted process, granitization states that granite is formed in place through extreme metasomatism by fluids bringing in elements, e.g. potassium, and removing others, e.g. calcium, to transform a metamorphic rock into a granite. This was supposed to occur across a migrating front.
After more than 50 years of studies, it becomes clear that granitic magmas have separated from their sources and experienced fractional crystallization during their ascent toward the surface. On the other hand, granitic melts can be produced in place through the partial melting of metamorphic rocks by extracting melt-mobile elements such as potassium and silicon into the melts but leaving others such as calcium and iron in granulite residues. Once a metamorphic rock is melted, it becomes a kind of migmatites which are composed of leucosome and melanosome.
In nature, metamorphic rocks may undergo partial melting to transform into migmatites through peritectic reactions, with anatectic melts to crystallize as leucosomes. As soon as the anatectic melts have separated from their sources and highly evolved through fractional crystallization during their ascent toward the surface, they become the magmatic melts and minerals of granitic composition.
After the extraction of anatectic melts, the migmatites become a kind of granulites. In all cases, the partial melting of solid rocks requires high temperatures, and also water or other volatiles which act as a catalyst by lowering the solidus temperature of these rocks. The production of granite at crustal depths requires high heat flow, which cannot be provided by heat production elements in the crust. Furthermore, high heat flow is necessary to produce granulite facies metamorphic rocks in orogens, indicating extreme metamorphism at high thermal gradients. In-situ granitisation by the extreme metamorphism is possible if crustal rocks would be heated by the asthenospheric mantle in rifting orogens, where collision-thickened orogenic lithosphere is thinned at first and then underwent extensional tectonism for active rifting.
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:
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.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.
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 fracture or fault systems and networks of active shear zones.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:
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 entirely by one or another mechanism.
Physical weathering occurs on a large scale in the form of exfoliation joints, which are the result of granite's expanding and fracturing as pressure is relieved when overlying material is removed by erosion or other processes.
Chemical weathering of granite occurs when dilute carbonic acid, and other acids present in rain and soil waters, alter feldspar in a process called hydrolysis.As demonstrated in the following reaction, this causes potassium feldspar to form kaolinite, with potassium ions, bicarbonate, and silica in solution as byproducts. An end product of granite weathering is grus, which is often made up of coarse-grained fragments of disintegrated granite.
Climatic variations also influence the weathering rate of granites. For about two thousand years, the relief engravings on Cleopatra's Needle obelisk had survived the arid conditions of its origin before its transfer to London. Within two hundred years, the red granite has drastically deteriorated in the damp and polluted air there.
Soil development on granite reflects the rock's high quartz content and dearth of available bases, with the base-poor status predisposing the soil to acidification and podzolization in cool humid climates as the weather-resistant quartz yields much sand.Feldspars also weather slowly in cool climes, allowing sand to dominate the fine-earth fraction. In warm humid regions, the weathering of feldspar as described above is accelerated so as to allow a much higher proportion of clay with the Cecil soil series a prime example of the consequent Ultisol great soil group.
Granite is a natural source of radiation, like most natural stones.
Potassium-40 is a radioactive isotope of weak emission, and a constituent of alkali feldspar, which in turn is a common component of granitic rocks, more abundant in alkali feldspar granite and syenites.
Some granites contain around 10 to 20 parts per million (ppm) of uranium. By contrast, more mafic rocks, such as tonalite, gabbro and diorite, have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts. Many large granite plutons are 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. Cellars and basements built into soils over granite can become a trap for radon gas,[ citation needed ] which is formed by the decay of uranium. Radon gas poses significant health concerns and is the number two cause of lung cancer in the US behind smoking.
Thorium occurs in all granites.Conway granite has been noted for its relatively high thorium concentration of 56±6 ppm.
There is some concern that some granite sold as countertops or building material may be hazardous to health. Dan Steck of St. Johns University has statedthat approximately 5% of all granite is of concern, with the caveat that only a tiny percentage of the tens of thousands of granite slab types have been tested. Various resources from national geological survey organizations 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.
A study of granite countertops was done (initiated and paid for by the Marble Institute of America) in November 2008 by National Health and Engineering Inc. of USA. In this test, all of the 39 full-size granite slabs that were measured for the study showed radiation levels well below the European Union safety standards (section 184.108.40.206 of the National Health and Engineering study) and radon emission levels well below the average outdoor radon concentrations in the US.
Granite and related marble industries are considered one of the oldest industries in the world; existing as far back as Ancient Egypt.
Major modern exporters of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain and the United States.
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, which is 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. Patrick Hunt has postulated that the Egyptians used emery, which has greater 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.
Imperial Roman granite was quarried mainly in Egypt, and also in Turkey, and on the islands of Elba and Giglio. Granite became "an integral part of the Roman language of monumental architecture".The quarrying ceased around the third century AD. Beginning in Late Antiquity the granite was reused, which since at least the early 16th century became known as spoliation. Through the process of case-hardening, granite becomes harder with age. The technology required to make tempered steel chisels was largely forgotten during the Middle Ages. As a result, Medieval stoneworkers were forced to use saws or emery to shorten ancient columns or hack them into discs. Giorgio Vasari noted in the 16th century that granite in quarries was "far softer and easier to work than after it has lain exposed" while ancient columns, because of their "hardness and solidity have nothing to fear from fire or sword, and time itself, that drives everything to ruin, not only has not destroyed them but has not even altered their colour."
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 be carved only 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 MacDonald's.As a result of the work of 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 stone known as "black granite" is usually gabbro, which has a completely different chemical composition.
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 in New England, granite was commonly used to build foundations for homes there. 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.
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 as the material of the tracks of the Haytor Granite Tramway, Devon, England, in 1820. Granite block is usually processed into slabs, which can be cut and shaped by a cutting center. Granite tables are used extensively as bases for optical instruments because of 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.
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 rarity of this 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 Scotland for curling stones.
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 the Yosemite Valley, the Bugaboos, the Mont Blanc massif (and peaks such as the Aiguille du Dru, the Mourne Mountains, the Adamello-Presanella Alps, the Aiguille du Midi and the Grandes Jorasses), the Bregaglia, Corsica, parts of the Karakoram (especially the Trango Towers), the Fitzroy Massif, Patagonia, Baffin Island, Ogawayama, the Cornish coast, the Cairngorms, Sugarloaf Mountain in Rio de Janeiro, Brazil, and the Stawamus Chief, British Columbia, Canada.
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.
Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma is produced by melting of the mantle and/or the crust at various tectonic settings, including subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During their storage in the crust, magma compositions may be modified by fractional crystallization, contamination with crustal melts, magma mixing, and degassing. Following their ascent through the crust, magmas may feed a volcano or solidify underground to form an intrusion. While the study of magma has historically relied on observing magma in the form of lava flows, magma has been encountered in situ three times during geothermal drilling projects—twice in Iceland, and once in Hawaii.
Andesite ( or ) is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and rhyolite, and ranges from 57 to 63% silicon dioxide (SiO2) as illustrated in TAS diagrams. The mineral assemblage is typically dominated by plagioclase plus pyroxene or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals. Alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other volcanic rocks are illustrated in QAPF diagrams.
Migmatite is a rock that is a mixture of metamorphic rock and igneous rock. It is created when a metamorphic rock such as gneiss partially melts, and then that melt recrystallizes into an igneous rock, creating a mixture of the unmelted metamorphic part with the recrystallized igneous part. They can also be known as diatexite.
Anorthosite is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.
Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure. They are of particular interest to geologists because many granulites represent samples of the deep continental crust. Some granulites experienced decompression from deep in the Earth to shallower crustal levels at high temperature; others cooled while remaining at depth in the Earth.
Charnockite is applied to any orthopyroxene-bearing quartz-feldspar rock, formed at high temperature and pressure, commonly found in granulite facies metamorphic regions, as an end-member of the charnockite series.
Essexite, also called nepheline monzogabbro, is a dark gray or black holocrystalline plutonic igneous rock. Its name is derived from the type locality in Essex County, Massachusetts, in the United States.
The rock cycle is a basic concept in geology that describes the transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. As the adjacent diagram illustrates, each of the types of rocks is altered or destroyed when it is forced out of its equilibrium conditions. An igneous rock such as basalt may break down and dissolve when exposed to the atmosphere, or melt as it is subducted under a continent. Due to the driving forces of the rock cycle, plate tectonics and the water cycle, rocks do not remain in equilibrium and are forced to change as they encounter new environments. The rock cycle is an illustration that explains how the three rock types are related to each other, and how processes change from one type to another over time. This cyclical aspect makes rock change a geologic cycle and, on planets containing life, a biogeochemical cycle.
Granophyre is a subvolcanic rock that contains quartz and alkali feldspar in characteristic angular intergrowths such as those in the accompanying image.
Anatexis in geology, refers to the differential, or partial, melting of rocks, especially in the forming of metamorphic rocks such as migmatites.
Restite is the residual material left at the site of melting during the in place production of granite through intense metamorphism.
In geology, igneous differentiation, or magmatic differentiation, is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement, or eruption.
Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within the Earth's crust and mantle. It is important in the formation of igneous rocks because it is one of the main processes of magmatic differentiation. Fractional crystallization is also important in the formation of sedimentary evaporite rocks.
Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO2 > 73%, and FeO + MgO + TiO2 < 2.4), weakly peraluminous (Al2O3/ (CaO + Na2O + K2O) = 0.98–1.11), and contain ilmenite, sphene, apatite and zircon as accessory minerals. Although the compositional range of the monzogranites is small, it defines a differentiation trend that is essentially controlled by biotite and plagioclase fractionation. (Fagiono, 2002). Monzogranites can be divided into two groups (magnesio-potassic monzogranite and ferro-potassic monzogranite) and are further categorized into rock types based on their macroscopic characteristics, melt characteristics, specific features, available isotopic data, and the locality in which they are found.
Leucogranite is a light-colored, granitic, igneous rock with almost no dark minerals. Alaskite is a synonym.
Alkali feldspar granite, some varieties of which are called 'red granite', is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of black minerals.
Tonalite-trondhjemite-granodiorite rocks or TTG rocks are intrusive rocks with typical granitic composition but containing only a small portion of potassium feldspar. Tonalite, trondhjemite, and granodiorite often occur together in geological records, indicating similar petrogenetic processes. Post Archean TTG rocks are present in arc-related batholiths, as well as in ophiolites, while Archean TTG rocks are major components of Archean cratons.
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