text:
Magma

Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as lava by laypeople) 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 or the crust in various tectonic settings, which on Earth include 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 magma's storage in the crust, its composition may be modified by fractional crystallization, contamination with crustal melts, magma mixing, and degassing. Following its ascent through the crust, magma may feed a volcano and be extruded as lava, or it may solidify underground to form an intrusion, such as a dike, a sill, a laccolith, a pluton, or a batholith.

While the study of magma has relied on observing magma after its transition into a lava flow, magma has been encountered in situ three times during geothermal drilling projects, twice in Iceland (see Use in energy production) and once in Hawaii.

Physical and chemical properties
Magma consists of liquid rock that usually contains suspended solid crystals. As magma approaches the surface and the overburden pressure drops, dissolved gases bubble out of the liquid, so that magma near the surface consists of materials in solid, liquid, and gas phases.

Composition
Most magma is rich in silica. Rare nonsilicate magma can form by local melting of nonsilicate mineral deposits or by separation of a magma into separate immiscible silicate and nonsilicate liquid phases.

Silicate magmas are molten mixtures dominated by oxygen and silicon, the most abundant chemical elements in the Earth's crust, with smaller quantities of aluminium, calcium, magnesium, iron, sodium, and potassium, and minor amounts of many other elements. Petrologists routinely express the composition of a silicate magma in terms of the weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the magma.

Because many of the properties of a magma (such as its viscosity and temperature) are observed to correlate with silica content, silicate magmas are divided into four chemical types based on silica content: felsic, intermediate, mafic, and ultramafic.

Felsic magmas
Felsic or silicic magmas have a silica content greater than 63%. They include rhyolite and dacite magmas. With such a high silica content, these magmas are extremely viscous, ranging from 108 cP (105 Pa⋅s) for hot rhyolite magma at 1200 C to 1011 cP (108 Pa⋅s) for cool rhyolite magma at 800 C. For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines, lava domes or "coulees" (which are thick, short lava flows). The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian.

Felsic lavas can erupt at temperatures as low as 800 °C. Unusually hot (>950 °C; >1,740 °F) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States.

Intermediate magmas
Intermediate or andesitic magmas contain 52% to 63% silica, and are lower in aluminium and usually somewhat richer in magnesium and iron than felsic magmas. Intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes, such as in the Andes. They are also commonly hotter, in the range of 850 to 1100 °C). Because of their lower silica content and higher eruptive temperatures, they tend to be much less viscous, with a typical viscosity of 3.5 × 106 cP (3,500 Pa⋅s) at 1200 C. This is slightly greater than the viscosity of smooth peanut butter. Intermediate magmas show a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, including amphibole or pyroxene phenocrysts.

Mafic magmas
Mafic or basaltic magmas have a silica content of 52% to 45%. They are typified by their high ferromagnesian content, and generally erupt at temperatures of 1100 to 1200 °C. Viscosities can be relatively low, around 104 to 105 cP (10 to 100 Pa⋅s), although this is still many orders of magnitude higher than water. This viscosity is similar to that of ketchup. Basalt lavas tend to produce low-profile shield volcanoes or flood basalts, because the fluidal lava flows for long distances from the vent. The thickness of a basalt lava, particularly on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath a solidified crust. Most basalt lavas are of ʻAʻā or pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas, which are rather similar to entrail-type pahoehoe lavas on land.

Ultramafic magmas
Ultramafic magmas, such as picritic basalt, komatiite, and highly magnesian magmas that form boninite, take the composition and temperatures to the extreme. All have a silica content under 45%. Komatiites contain over 18% magnesium oxide, and are thought to have erupted at temperatures of 1600 °C. At this temperature there is practically no polymerization of the mineral compounds, creating a highly mobile liquid. Viscosities of komatiite magmas are thought to have been as low as 100 to 1000 cP (0.1 to 1 Pa⋅s), similar to that of light motor oil. Most ultramafic lavas are no younger than the Proterozoic, with a few ultramafic magmas known from the Phanerozoic in Central America that are attributed to a hot mantle plume. No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce highly magnesian magmas.

Alkaline magmas
Some silicic magmas have an elevated content of alkali metal oxides (sodium and potassium), particularly in regions of continental rifting, areas overlying deeply subducted plates, or at intraplate hotspots. Their silica content can range from ultramafic (nephelinites, basanites and tephrites) to felsic (trachytes). They are more likely to be generated at greater depths in the mantle than subalkaline magmas. Olivine nephelinite magmas are both ultramafic and highly alkaline, and are thought to have come from much deeper in the mantle of the Earth than other magmas.

Non-silicate magmas
Some lavas of unusual composition have erupted onto the surface of the Earth. These include:
 * Carbonatite and natrocarbonatite lavas are known from Ol Doinyo Lengai volcano in Tanzania, which is the sole example of an active carbonatite volcano. Carbonatites in the geologic record are typically 75% carbonate minerals, with lesser amounts of silica-undersaturated silicate minerals (such as micas and olivine), apatite, magnetite, and pyrochlore. This may not reflect the original composition of the lava, which may have included sodium carbonate that was subsequently removed by hydrothermal activity, though laboratory experiments show that a calcite-rich magma is possible. Carbonatite lavas show stable isotope ratios indicating they are derived from the highly alkaline silicic lavas with which they are always associated, probably by separation of an immiscible phase. Natrocarbonatite lavas of Ol Doinyo Lengai are composed mostly of sodium carbonate, with about half as much calcium carbonate and half again as much potassium carbonate, and minor amounts of halides, fluorides, and sulphates. The lavas are extremely fluid, with viscosities only slightly greater than water, and are very cool, with measured temperatures of 491 to 544 C.
 * Iron oxide magmas are thought to be the source of the iron ore at Kiruna, Sweden which formed during the Proterozoic. Iron oxide lavas of Pliocene age occur at the El Laco volcanic complex on the Chile-Argentina border. Iron oxide lavas are thought to be the result of immiscible separation of iron oxide magma from a parental magma of calc-alkaline or alkaline composition. When erupted, the temperature of the molten iron oxide magma is about 700 to 800 C.
 * Sulfur lava flows up to 250 m long and 10 m wide occur at Lastarria volcano, Chile. They were formed by the melting of sulfur deposits at temperatures as low as 113 °C.

Magmatic gases
The concentrations of different gases can vary considerably. Water vapor is typically the most abundant magmatic gas, followed by carbon dioxide and sulfur dioxide. Other principal magmatic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride.

The solubility of magmatic gases in magma depends on pressure, magma composition, and temperature. Magma that is extruded as lava is extremely dry, but magma at depth and under great pressure can contain a dissolved water content in excess of 10%. Water is somewhat less soluble in low-silica magma than high-silica magma, so that at 1,100 °C and 0.5 GPa, a basaltic magma can dissolve 8% H2O while a granite pegmatite magma can dissolve 11% H2O. However, magmas are not necessarily saturated under typical conditions.

Carbon dioxide is much less soluble in magmas than water, and frequently separates into a distinct fluid phase even at great depth. This explains the presence of carbon dioxide fluid inclusions in crystals formed in magmas at great depth.

Rheology
Viscosity is a key melt property in understanding the behaviour of magmas. Whereas temperatures in common silicate lavas range from about 800 C for felsic lavas to 1200 C for mafic lavas, the viscosity of the same lavas ranges over seven orders of magnitude, from 104 cP (10 Pa⋅s) for mafic lava to 1011 cP (108 Pa⋅s) for felsic magmas. The viscosity is mostly determined by composition but is also dependent on temperature. The tendency of felsic lava to be cooler than mafic lava increases the viscosity difference.

The silicon ion is small and highly charged, and so it has a strong tendency to coordinate with four oxygen ions, which form a tetrahedral arrangement around the much smaller silicon ion. This is called a silica tetrahedron. In a magma that is low in silicon, these silica tetrahedra are isolated, but as the silicon content increases, silica tetrahedra begin to partially polymerize, forming chains, sheets, and clumps of silica tetrahedra linked by bridging oxygen ions. These greatly increase the viscosity of the magma.

The tendency towards polymerization is expressed as NBO/T, where NBO is the number of non-bridging oxygen ions and T is the number of network-forming ions. Silicon is the main network-forming ion, but in magmas high in sodium, aluminium also acts as a network former, and ferric iron can act as a network former when other network formers are lacking. Most other metallic ions reduce the tendency to polymerize and are described as network modifiers. In a hypothetical magma formed entirely from melted silica, NBO/T would be 0, while in a hypothetical magma so low in network formers that no polymerization takes place, NBO/T would be 4. Neither extreme is common in nature, but basalt magmas typically have NBO/T between 0.6 and 0.9, andesitic magmas have NBO/T of 0.3 to 0.5, and rhyolitic magmas have NBO/T of 0.02 to 0.2. Water acts as a network modifier, and dissolved water drastically reduces melt viscosity. Carbon dioxide neutralizes network modifiers, so dissolved carbon dioxide increases the viscosity. Higher-temperature melts are less viscous, since more thermal energy is available to break bonds between oxygen and network formers.

Most magmas contain solid crystals of various minerals, fragments of exotic rocks known as xenoliths and fragments of previously solidified magma. The crystal content of most magmas gives them thixotropic and shear thinning properties. In other words, most magmas do not behave like Newtonian fluids, in which the rate of flow is proportional to the shear stress. Instead, a typical magma is a Bingham fluid, which shows considerable resistance to flow until a stress threshold, called the yield stress, is crossed. This results in plug flow of partially crystalline magma. A familiar example of plug flow is toothpaste squeezed out of a toothpaste tube. The toothpaste comes out as a semisolid plug, because shear is concentrated in a thin layer in the toothpaste next to the tube, and only here does the toothpaste behave as a fluid. Thixotropic behavior also hinders crystals from settling out of the magma. Once the crystal content reaches about 60%, the magma ceases to behave like a fluid and begins to behave like a solid. Such a mixture of crystals with melted rock is sometimes described as crystal mush.

Magma is typically also viscoelastic, meaning it flows like a liquid under low stresses, but once the applied stress exceeds a critical value, the melt cannot dissipate the stress fast enough through relaxation alone, resulting in transient fracture propagation. Once stresses are reduced below the critical threshold, the melt viscously relaxes once more and heals the fracture.

Temperature
Temperatures of molten lava, which is magma extruded onto the surface, are almost all in the range 700 to 1400 C, but very rare carbonatite magmas may be as cool as 490 C, and komatiite magmas may have been as hot as 1600 C. Magma has occasionally been encountered during drilling in geothermal fields, including drilling in Hawaii that penetrated a dacitic magma body at a depth of 2488 m. The temperature of this magma was estimated at 1050 C. Temperatures of deeper magmas must be inferred from theoretical computations and the geothermal gradient.

Most magmas contain some solid crystals suspended in the liquid phase. This indicates that the temperature of the magma lies between the solidus, which is defined as the temperature at which the magma completely solidifies, and the liquidus, defined as the temperature at which the magma is completely liquid. Calculations of solidus temperatures at likely depths suggests that magma generated beneath areas of rifting starts at a temperature of about 1300 to 1500 C. Magma generated from mantle plumes may be as hot as 1600 C. The temperature of magma generated in subduction zones, where water vapor lowers the melting temperature, may be as low as 1060 C.

Density
Magma densities depend mostly on composition, iron content being the most important parameter.

Magma expands slightly at lower pressure or higher temperature. When magma approaches the surface, its dissolved gases begin to bubble out of the liquid. These bubbles had significantly reduced the density of the magma at depth and helped drive it toward the surface in the first place.

Origins
The temperature within the interior of the earth is described by the geothermal gradient, which is the rate of temperature change with depth. The geothermal gradient is established by the balance between heating through radioactive decay in the Earth's interior and heat loss from the surface of the earth. The geothermal gradient averages about 25 °C/km in the Earth's upper crust, but this varies widely by region, from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km along mid-ocean ridges or near mantle plumes. The gradient becomes less steep with depth, dropping to just 0.25 to 0.3 °C/km in the mantle, where slow convection efficiently transports heat. The average geothermal gradient is not normally steep enough to bring rocks to their melting point anywhere in the crust or upper mantle, so magma is produced only where the geothermal gradient is unusually steep or the melting point of the rock is unusually low. However, the ascent of magma towards the surface in such settings is the most important process for transporting heat through the crust of the Earth.

Rocks may melt in response to a decrease in pressure, to a change in composition (such as an addition of water), to an increase in temperature, or to a combination of these processes. Other mechanisms, such as melting from a meteorite impact, are less important today, but impacts during the accretion of the Earth led to extensive melting, and the outer several hundred kilometers of the early Earth was probably a magma ocean. Impacts of large meteorites in the last few hundred million years have been proposed as one mechanism responsible for the extensive basalt magmatism of several large igneous provinces.

Decompression
Decompression melting occurs because of a decrease in pressure. It is the most important mechanism for producing magma from the upper mantle.

The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. Peridotite at depth in the Earth's mantle may be hotter than its solidus temperature at some shallower level. If such rock rises during the convection of solid mantle, it will cool slightly as it expands in an adiabatic process, but the cooling is only about 0.3 °C per kilometer. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3 °C to 4 °C per kilometer. If the rock rises far enough, it will begin to melt. Melt droplets can coalesce into larger volumes and be intruded upwards. This process of melting from the upward movement of solid mantle is critical in the evolution of the Earth.

Decompression melting creates the ocean crust at mid-ocean ridges, making it by far the most important source of magma on Earth. It also causes volcanism in intraplate regions, such as Europe, Africa and the Pacific sea floor. Intraplate volcanism is attributed to the rise of mantle plumes or to intraplate extension, with the importance of each mechanism being a topic of continuing research.

Effects of water and carbon dioxide
The change of rock composition most responsible for the creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800 °C in the presence of excess water, but near 1,500 °C in the absence of water. Water is driven out of the oceanic lithosphere in subduction zones, and it causes melting in the overlying mantle. Hydrous magmas with the composition of basalt or andesite are produced directly and indirectly as results of dehydration during the subduction process. Such magmas, and those derived from them, build up island arcs such as those in the Pacific Ring of Fire. These magmas form rocks of the calc-alkaline series, an important part of the continental crust. With low density and viscosity, hydrous magmas are highly buoyant and will move upwards in Earth's mantle.

The addition of carbon dioxide is relatively a much less important cause of magma formation than the addition of water, but genesis of some silica-undersaturated magmas has been attributed to the dominance of carbon dioxide over water in their mantle source regions. In the presence of carbon dioxide, experiments document that the peridotite solidus temperature decreases by about 200 °C in a narrow pressure interval at pressures corresponding to a depth of about 70 km. At greater depths, carbon dioxide can have more effect: at depths to about 200 km, the temperatures of initial melting of a carbonated peridotite composition were determined to be 450 °C to 600 °C lower than for the same composition with no carbon dioxide. Magmas of rock types such as nephelinite, carbonatite, and kimberlite are among those that may be generated following an influx of carbon dioxide into mantle at depths greater than about 70 km.

Temperature increase
Increase in temperature is the most typical mechanism for formation of magma within continental crust. Such temperature increases can occur because of the upward intrusion of magma from the mantle. Temperatures can also exceed the solidus of a crustal rock in continental crust thickened by compression at a plate boundary. The plate boundary between the Indian and Asian continental masses provides a well-studied example, as the Tibetan Plateau just north of the boundary has crust about 80 kilometers thick, roughly twice the thickness of normal continental crust. Studies of electrical resistivity deduced from magnetotelluric data have detected a layer that appears to contain silicate melt and that stretches for at least 1,000 kilometers within the middle crust along the southern margin of the Tibetan Plateau. Granite and rhyolite are types of igneous rock commonly interpreted as products of the melting of continental crust because of increases in temperature. Temperature increases also may contribute to the melting of lithosphere dragged down in a subduction zone.

The melting process
When rocks melt, they do so over a range of temperature, because most rocks are made of several minerals, which all have different melting points. The temperature at which the first melt appears (the solidus) is lower than the melting temperature of any one of the pure minerals. This is similar to the lowering of the melting point of ice when it is mixed with salt. The first melt is called the eutectic and has a composition that depends on the combination of minerals present.

For example, a mixture of anorthite and diopside, which are two of the predominant minerals in basalt, begins to melt at about 1274 °C. This is well below the melting temperatures of 1392 °C for pure diopside and 1553 °C for pure anorthite. The resulting melt is composed of about 43 wt% anorthite. As additional heat is added to the rock, the temperature remains at 1274 °C until either the anorthite or diopside is fully melted. The temperature then rises as the remaining mineral continues to melt, which shifts the melt composition away from the eutectic. For example, if the content of anorthite is greater than 43%, the entire supply of diopside will melt at 1274 °C., along with enough of the anorthite to keep the melt at the eutectic composition. Further heating causes the temperature to slowly rise as the remaining anorthite gradually melts and the melt becomes increasingly rich in anorthite liquid. If the mixture has only a slight excess of anorthite, this will melt before the temperature rises much above 1274 °C. If the mixture is almost all anorthite, the temperature will reach nearly the melting point of pure anorthite before all the anorthite is melted. If the anorthite content of the mixture is less than 43%, then all the anorthite will melt at the eutectic temperature, along with part of the diopside, and the remaining diopside will then gradually melt as the temperature continues to rise.

Because of eutectic melting, the composition of the melt can be quite different from the source rock. For example, a mixture of 10% anorthite with diopside could experience about 23% partial melting before the melt deviated from the eutectic, which has the composition of about 43% anorthite. This effect of partial melting is reflected in the compositions of different magmas. A low degree of partial melting of the upper mantle (2% to 4%) can produce highly alkaline magmas such as melilitites, while a greater degree of partial melting (8% to 11%) can produce alkali olivine basalt. Oceanic magmas likely result from partial melting of 3% to 15% of the source rock. Some calk-alkaline granitoids may be produced by a high degree of partial melting, as much as 15% to 30%. High-magnesium magmas, such as komatiite and picrite, may also be the products of a high degree of partial melting of mantle rock.

Certain chemical elements, called incompatible elements, have a combination of ionic radius and ionic charge that is unlike that of the more abundant elements in the source rock. The ions of these elements fit rather poorly in the structure of the minerals making up the source rock, and readily leave the solid minerals to become highly concentrated in melts produced by a low degree of partial melting. Incompatible elements commonly include potassium, barium, caesium, and rubidium, which are large and weakly charged (the large-ion lithophile elements, or LILEs), as well as elements whose ions carry a high charge (the high-field-strength elements, or HSFEs), which include such elements as zirconium, niobium, hafnium, tantalum, the rare-earth elements, and the actinides. Potassium can become so enriched in melt produced by a very low degree of partial melting that, when the magma subsequently cools and solidifies, it forms unusual potassic rock such as lamprophyre, lamproite, or kimberlite.

When enough rock is melted, the small globules of melt (generally occurring between mineral grains) link up and soften the rock. Under pressure within the earth, as little as a fraction of a percent of partial melting may be sufficient to cause melt to be squeezed from its source. Melt rapidly separates from its source rock once the degree of partial melting exceeds 30%. However, usually much less than 30% of a magma source rock is melted before the heat supply is exhausted.

Pegmatite may be produced by low degrees of partial melting of the crust. Some granite-composition magmas are eutectic (or cotectic) melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization.

Evolution of magmas

Most magmas are fully melted only for small parts of their histories. More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve.

As magma cools, minerals typically crystallize from the melt at different temperatures. This resembles the original melting process in reverse. However, because the melt has usually separated from its original source rock and moved to a shallower depth, the reverse process of crystallization is not precisely identical. For example, if a melt was 50% each of diopside and anorthite, then anorthite would begin crystallizing from the melt at a temperature somewhat higher than the eutectic temperature of 1274 °C. This shifts the remaining melt towards its eutectic composition of 43% diopside. The eutectic is reached at 1274 °C, the temperature at which diopside and anorthite begin crystallizing together. If the melt was 90% diopside, the diopside would begin crystallizing first until the eutectic was reached.

If the crystals remained suspended in the melt, the crystallization process would not change the overall composition of the melt plus solid minerals. This situation is described as equillibrium crystallization. However, in a series of experiments culminating in his 1915 paper, Crystallization-differentiation in silicate liquids, Norman L. Bowen demonstrated that crystals of olivine and diopside that crystallized out of a cooling melt of forsterite, diopside, and silica would sink through the melt on geologically relevant time scales. Geologists subsequently found considerable field evidence of such fractional crystallization.

When crystals separate from a magma, then the residual magma will differ in composition from the parent magma. For instance, a magma of gabbroic composition can produce a residual melt of granitic composition if early formed crystals are separated from the magma. Gabbro may have a liquidus temperature near 1,200 °C, and the derivative granite-composition melt may have a liquidus temperature as low as about 700 °C. Incompatible elements are concentrated in the last residues of magma during fractional crystallization and in the first melts produced during partial melting: either process can form the magma that crystallizes to pegmatite, a rock type commonly enriched in incompatible elements. Bowen's reaction series is important for understanding the idealised sequence of fractional crystallisation of a magma.

Magma composition can be determined by processes other than partial melting and fractional crystallization. For instance, magmas commonly interact with rocks they intrude, both by melting those rocks and by reacting with them. Assimilation near the roof of a magma chamber and fractional crystallization near its base can even take place simultaneously. Magmas of different compositions can mix with one another. In rare cases, melts can separate into two immiscible melts of contrasting compositions.

Primary magmas
When rock melts, the liquid is a primary magma. Primary magmas have not undergone any differentiation and represent the starting composition of a magma. In practice, it is difficult to unambiguously identify primary magmas, though it has been suggested that boninite is a variety of andesite crystallized from a primary magma. The Great Dyke of Zimbabwe has also been interpreted as rock crystallized from a primary magma. The interpretation of leucosomes of migmatites as primary magmas is contradicted by zircon data, which suggests leucosomes are a residue (a cumulate rock) left by extraction of a primary magma.

Parental magma
When it is impossible to find the primitive or primary magma composition, it is often useful to attempt to identify a parental magma. A parental magma is a magma composition from which the observed range of magma chemistries has been derived by the processes of igneous differentiation. It need not be a primitive melt.

For instance, a series of basalt flows are assumed to be related to one another. A composition from which they could reasonably be produced by fractional crystallization is termed a parental magma. Fractional crystallization models would be produced to test the hypothesis that they share a common parental magma.

Migration and solidification
Magma develops within the mantle or crust where the temperature and pressure conditions favor the molten state. After its formation, magma buoyantly rises toward the Earth's surface, due to its lower density than the source rock. As it migrates through the crust, magma may collect and reside in magma chambers (though recent work suggests that magma may be stored in trans-crustal crystal-rich mush zones rather than dominantly liquid magma chambers ). Magma can remain in a chamber until it either cools and crystallizes to form intrusive rock, it erupts as a volcano, or it moves into another magma chamber.

Plutonism
When magma cools it begins to form solid mineral phases. Some of these settle at the bottom of the magma chamber forming cumulates that might form mafic layered intrusions. Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt, andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite, respectively).

Volcanism
Magma that is extruded onto the surface during a volcanic eruption is called lava. Lava cools and solidifies relatively quickly compared to underground bodies of magma. This fast cooling does not allow crystals to grow large, and a part of the melt does not crystallize at all, becoming glass. Rocks largely composed of volcanic glass include obsidian, scoria and pumice.

Before and during volcanic eruptions, volatiles such as CO2 and H2O partially leave the melt through a process known as exsolution. Magma with low water content becomes increasingly viscous. If massive exsolution occurs when magma heads upwards during a volcanic eruption, the resulting eruption is usually explosive.

Use in energy production
The Iceland Deep Drilling Project, while drilling several 5,000 m holes in an attempt to harness the heat in the volcanic bedrock below the surface of Iceland, struck a pocket of magma at 2,100 m in 2009. Because this was only the third time in recorded history that magma had been reached, IDDP decided to invest in the hole, naming it IDDP-1.

A cemented steel case was constructed in the hole with a perforation at the bottom close to the magma. The high temperatures and pressure of the magma steam were used to generate 36 MW of power, making IDDP-1 the world's first magma-enhanced geothermal system.

title: Magma


text:
Respiration

Respiration may refer to:

Biology

 * Cellular respiration, the process in which nutrients are converted into useful energy in a cell
 * Anaerobic respiration, cellular respiration without oxygen
 * Maintenance respiration, the amount of cellular respiration required for an organism to maintain itself in a constant state
 * Respiration (physiology), transporting oxygen and carbon dioxide between cells and the external environment
 * Respiratory system, the anatomical system of an organism used for respiration
 * Breathing, passing air in and out through respiratory organs
 * Aquatic respiration, animals extracting oxygen from water
 * Artificial respiration, the act of simulating respiration, which provides for the overall exchange of gases in the body by pulmonary ventilation, external respiration and internal respiration
 * Cheyne–Stokes respiration, an abnormal pattern of breathing characterized by progressively deeper and sometimes faster breathing, followed by a gradual decrease that results in a temporary stop in breathing called an apnea
 * Respiration, a journal by Karger Publishers

Ecology

 * Carbon respiration, a concept used in calculating carbon (as ) flux occurring in the atmosphere
 * Ecosystem respiration, measurement of gross carbon dioxide production by all organisms in an ecosystem
 * Root respiration, exchange of gases between plant roots and the atmosphere
 * Photorespiration, enzymatic combination of RuBP with oxygen

Entertainment

 * "Respiration" (song), a 1999 single by Black Star
 * "Respire" (song), a 2003 song by Mickey 3D
 * Respire (film), a 2014 French drama film
 * Respiration (album), a 2022 album by Cecil Taylor

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Respiration


text:
Adjective

An adjective (abbreviated adj.) is a word that describes or defines a noun or noun phrase. Its semantic role is to change information given by the noun.

Traditionally, adjectives are considered one of the main parts of speech of the English language, although historically they were classed together with nouns. Nowadays, certain words that usually had been classified as adjectives, including the, this, my, etc., typically are classed separately, as determiners.

Here are some examples:
 * That's a funny idea. (attributive)
 * That idea is funny. (predicative)
 * Tell me something funny. (postpositive)
 * The good, the bad, and the funny. (substantive)

Etymology
Adjective comes from Latin nōmen adjectīvum, a calque of ἐπίθετον ὄνομα (surname) (whence also English epithet). In the grammatical tradition of Latin and Greek, because adjectives were inflected for gender, number, and case like nouns (a process called declension), they were considered a type of noun. The words that are today typically called nouns were then called substantive nouns (nōmen substantīvum). The terms noun substantive and noun adjective were formerly used in English but are now obsolete.

Types of use
Depending on the language, an adjective can precede a corresponding noun on a prepositive basis or it can follow a corresponding noun on a postpositive basis. Structural, contextual, and style considerations can impinge on the pre-or post-position of an adjective in a given instance of its occurrence. In English, occurrences of adjectives generally can be classified into one of three categories:
 * Prepositive adjectives, which are also known as "attributive adjectives", occur on an antecedent basis within noun phrases. For example: "I put my happy kids into the car", wherein happy occurs on an antecedent basis within the my happy kids noun phrase, and therefore functions in a prepositive adjective.
 * Postpositive adjectives can occur: immediately subsequent to a noun within a noun phrase, e.g. "The only room available cost twice what we expected";  as linked via a copula or other linking mechanism subsequent to a corresponding noun or pronoun; for example: "My kids are happy", wherein happy is a predicate adjective (see also: Predicative expression, Subject complement); or  as an appositive adjective within a noun phrase, e.g. "My kids, [who are] happy to go for a drive, are in the back seat."
 * Nominalized adjectives, which function as nouns. One way this happens is by eliding a noun from an adjective-noun noun phrase, whose remnant thus is a nominalization. In the sentence, "I read two books to them; he preferred the sad book, but she preferred the happy", happy is a nominalized adjective, short for "happy one" or "happy book". Another way this happens is in phrases like "out with the old, in with the new", where "the old" means "that which is old" or "all that is old", and similarly with "the new". In such cases, the adjective may function as a mass noun (as in the preceding example). In English, it may also function as a plural count noun denoting a collective group, as in "The meek shall inherit the Earth", where "the meek" means "those who are meek" or "all who are meek".

Distribution
Adjectives feature as a part of speech (word class) in most languages. In some languages, the words that serve the semantic function of adjectives are categorized together with some other class, such as nouns or verbs. In the phrase "a Ford car", "Ford" is unquestionably a noun but its function is adjectival: to modify "car". In some languages adjectives can function as nouns: for example, the Spanish phrase "un rojo" means "a red [one]".

As for "confusion" with verbs, rather than an adjective meaning "big", a language might have a verb that means "to be big" and could then use an attributive verb construction analogous to "big-being house" to express what in English is called a "big house". Such an analysis is possible for the grammar of Standard Chinese and Korean, for example.

Different languages do not use adjectives in exactly the same situations. For example, where English uses "to be hungry" (hungry being an adjective), Dutch, French, and Spanish use "honger hebben", "avoir faim", and "tener hambre" respectively (literally "to have hunger", the words for "hunger" being nouns). Similarly, where Hebrew uses the adjective (zaqūq, roughly "in need of" or "needing"), English uses the verb "to need".

In languages that have adjectives as a word class, it is usually an open class; that is, it is relatively common for new adjectives to be formed via such processes as derivation. However, Bantu languages are well known for having only a small closed class of adjectives, and new adjectives are not easily derived. Similarly, native Japanese adjectives (i-adjectives) are considered a closed class (as are native verbs), although nouns (an open class) may be used in the genitive to convey some adjectival meanings, and there is also the separate open class of adjectival nouns (na-adjectives).

Adverbs
Many languages (including English) distinguish between adjectives, which qualify nouns and pronouns, and adverbs, which mainly modify verbs, adjectives, or other adverbs. Not all languages make this exact distinction; many (including English) have words that can function as either. For example, in English, fast is an adjective in "a fast car" (where it qualifies the noun car) but an adverb in "he drove fast" (where it modifies the verb drove).

In Dutch and German, adjectives and adverbs are usually identical in form and many grammarians do not make the distinction, but patterns of inflection can suggest a difference:
 * Eine kluge neue Idee.
 * A clever new idea.
 * Eine klug ausgereifte Idee.
 * A cleverly developed idea.

A German word like klug ("clever(ly)") takes endings when used as an attributive adjective but not when used adverbially. Whether these are distinct parts of speech or distinct usages of the same part of speech is a question of analysis. While German linguistic terminology distinguishes adverbiale from adjektivische Formen, German refers to both as Eigenschaftswörter ("property words").

Determiners
Linguists today distinguish determiners from adjectives, considering them to be two separate parts of speech (or lexical categories). Determiners formerly were considered to be adjectives in some of their uses. Determiners function neither as nouns nor pronouns but instead characterize a nominal element within a particular context. They generally do this by indicating definiteness (a vs. the), quantity (one vs. some vs. many), or another such property.

Adjective phrases
An adjective acts as the head of an adjective phrase or adjectival phrase (AP). In the simplest case, an adjective phrase consists solely of the adjective; more complex adjective phrases may contain one or more adverbs modifying the adjective ("very strong"), or one or more complements (such as "worth several dollars", "full of toys", or "eager to please"). In English, attributive adjective phrases that include complements typically follow the noun that they qualify ("an evildoer devoid of redeeming qualities").

Other modifiers of nouns
In many languages (including English) it is possible for nouns to modify other nouns. Unlike adjectives, nouns acting as modifiers (called attributive nouns or noun adjuncts) usually are not predicative; a beautiful park is beautiful, but a car park is not "car". The modifier often indicates origin ("Virginia reel"), purpose ("work clothes"), semantic patient ("man eater") or semantic subject ("child actor"); however, it may generally indicate almost any semantic relationship. It is also common for adjectives to be derived from nouns, as in boyish, birdlike, behavioral (behavioural), famous, manly, angelic, and so on.

In Australian Aboriginal languages, the distinction between adjectives and nouns is typically thought weak, and many of the languages only use nouns—or nouns with a limited set of adjective-deriving affix es—to modify other nouns. In languages that have a subtle adjective-noun distinction, one way to tell them apart is that a modifying adjective can come to stand in for an entire elided noun phrase, while a modifying noun cannot. For example, in Bardi, the adjective moorrooloo 'little' in the phrase moorrooloo baawa 'little child' can stand on its own to mean 'the little one,' while the attributive noun aamba 'man' in the phrase aamba baawa 'male child' cannot stand for the whole phrase to mean 'the male one.' In other languages, like Warlpiri, nouns and adjectives are lumped together beneath the nominal umbrella because of their shared syntactic distribution as arguments of predicates. The only thing distinguishing them is that some nominals seem to semantically denote entities (typically nouns in English) and some nominals seem to denote attributes (typically adjectives in English).

Many languages have participle forms that can act as noun modifiers either alone or as the head of a phrase. Sometimes participles develop into functional usage as adjectives. Examples in English include relieved (the past participle of relieve), used as an adjective in passive voice constructs such as "I am so relieved to see you". Other examples include spoken (the past participle of speak) and going (the present participle of go), which function as attribute adjectives in such phrases as "the spoken word" and "the going rate".

Other constructs that often modify nouns include prepositional phrases (as in "a rebel without a cause"), relative clauses (as in "the man who wasn't there"), and infinitive phrases (as in "a cake to die for"). Some nouns can also take complements such as content clauses (as in "the idea that I would do that"), but these are not commonly considered modifiers. For more information about possible modifiers and dependents of nouns, see Components of noun phrases.

Order
In many languages, attributive adjectives usually occur in a specific order. In general, the adjective order in English can be summarised as: opinion, size, age or shape, colour, origin, material, purpose. Other language authorities, like the Cambridge Dictionary, state that shape precedes rather than follows age.

Determiners and postdeterminers—articles, numerals, and other limiters (e.g. three blind mice)—come before attributive adjectives in English. Although certain combinations of determiners can appear before a noun, they are far more circumscribed than adjectives in their use—typically, only a single determiner would appear before a noun or noun phrase (including any attributive adjectives).

 * 1) Opinion – limiter adjectives (e.g. a real hero, a perfect idiot) and adjectives of subjective measure (e.g. beautiful, interesting) or value (e.g. good, bad, costly)
 * 2) Size – adjectives denoting physical size (e.g. tiny, big, extensive)
 * 3) Shape or physical quality – adjectives describing more detailed physical attributes than overall size (e.g. round, sharp, swollen, thin)
 * 4) Age – adjectives denoting age (e.g. young, old, new, ancient, six-year-old)
 * 5) Colour – adjectives denoting colour or pattern (e.g. white, black, pale, spotted)
 * 6) Origin – denominal adjectives denoting source (e.g. Japanese, volcanic, extraterrestrial)
 * 7) Material – denominal adjectives denoting what something is made of (e.g., woollen, metallic, wooden)
 * 8) Qualifier/purpose – final limiter, which sometimes forms part of the (compound) noun (e.g., rocking chair, hunting cabin, passenger car, book cover)

This means that, in English, adjectives pertaining to size precede adjectives pertaining to age ("little old", not "old little"), which in turn generally precede adjectives pertaining to colour ("old white", not "white old"). So, one would say "One (quantity) nice (opinion) little (size) old (age) round (shape) [or round old] white (colour) brick (material) house." When several adjectives of the same type are used together, they are ordered from general to specific, like "lovely intelligent person" or "old medieval castle".

This order may be more rigid in some languages than others; in some, like Spanish, it may only be a default (unmarked) word order, with other orders being permissible. Other languages, such as Tagalog, follow their adjectival orders as rigidly as English.

The normal adjectival order of English may be overridden in certain circumstances, especially when one adjective is being fronted. For example, the usual order of adjectives in English would result in the phrase "the bad big wolf" (opinion before size), but instead, the usual phrase is "the big bad wolf".

Owing partially to borrowings from French, English has some adjectives that follow the noun as postmodifiers, called postpositive adjectives, as in time immemorial and attorney general. Adjectives may even change meaning depending on whether they precede or follow, as in proper: They live in a proper town (a real town, not a village) vs. They live in the town proper (in the town itself, not in the suburbs). All adjectives can follow nouns in certain constructions, such as tell me something new.

Comparison (degrees)
In many languages, some adjectives are comparable and the measure of comparison is called degree. For example, a person may be "polite", but another person may be "more polite", and a third person may be the "most polite" of the three. The word "more" here modifies the adjective "polite" to indicate a comparison is being made, and "most" modifies the adjective to indicate an absolute comparison (a superlative).

Among languages that allow adjectives to be compared, different means are used to indicate comparison. Some languages do not distinguish between comparative and superlative forms. Other languages allow adjectives to be compared but do not have a special comparative form of the adjective. In such cases, as in some Australian Aboriginal languages, case-marking, such as the ablative case may be used to indicate one entity has more of an adjectival quality than (i.e. from—hence ABL) another. Take the following example in Bardi:

In English, many adjectives can be inflected to comparative and superlative forms by taking the suffixes "-er" and "-est" (sometimes requiring additional letters before the suffix; see forms for far below), respectively:

 * "great", "greater", "greatest"
 * "deep", "deeper", "deepest"

Some adjectives are irregular in this sense:
 * "good", "better", "best"
 * "bad", "worse", "worst"
 * "many", "more", "most" (sometimes regarded as an adverb or determiner)
 * "little", "less", "least"

Some adjectives can have both regular and irregular variations:
 * "old", "older", "oldest"
 * "far", "farther", "farthest"

also
 * "old", "elder", "eldest"
 * "far", "further", "furthest"

Another way to convey comparison is by incorporating the words "more" and "most". There is no simple rule to decide which means is correct for any given adjective, however. The general tendency is for simpler adjectives and those from Anglo-Saxon to take the suffixes, while longer adjectives and those from French, Latin, or Greek do not—but sometimes sound of the word is the deciding factor.

Many adjectives do not naturally lend themselves to comparison. For example, some English speakers would argue that it does not make sense to say that one thing is "more ultimate" than another, or that something is "most ultimate", since the word "ultimate" is already absolute in its semantics. Such adjectives are called non-comparable or absolute. Nevertheless, native speakers will frequently play with the raised forms of adjectives of this sort. Although "pregnant" is logically non-comparable (either one is pregnant or not), one may hear a sentence like "She looks more and more pregnant each day".

Comparative and superlative forms are also occasionally used for other purposes than comparison. In English comparatives can be used to suggest that a statement is only tentative or tendential: one might say "John is more the shy-and-retiring type", where the comparative "more" is not really comparing him with other people or with other impressions of him, but rather, could be substituting for "on the whole" or "more so than not". In Italian, superlatives are frequently used to put strong emphasis on an adjective: bellissimo means "most beautiful", but is in fact more commonly heard in the sense "extremely beautiful".

Restrictiveness
Attributive adjectives and other noun modifiers may be used either restrictively (helping to identify the noun's referent, hence "restricting" its reference) or non-restrictively (helping to describe a noun). For example:

 * "He was a lazy sort, who would avoid a difficult task and fill his working hours with easy ones."

Here "difficult" is restrictive – it tells which tasks he avoids, distinguishing these from the easy ones: "Only those tasks that are difficult".
 * "She had the job of sorting out the mess left by her predecessor, and she performed this difficult task with great acumen."

Here difficult is non-restrictive – it is already known which task it was, but the adjective describes it more fully: "The aforementioned task, which (by the way) is difficult."

In some languages, such as Spanish, restrictiveness is consistently marked; for example, in Spanish la tarea difícil means "the difficult task" in the sense of "the task that is difficult" (restrictive), whereas la difícil tarea means "the difficult task" in the sense of "the task, which is difficult" (non-restrictive). In English, restrictiveness is not marked on adjectives but is marked on relative clauses (the difference between "the man who recognized me was there" and "the man, who recognized me, was there" being one of restrictiveness).

Agreement
In some languages, adjectives alter their form to reflect the gender, case and number of the noun that they describe. This is called agreement or concord. Usually it takes the form of inflections at the end of the word, as in Latin:

 * {|border=0

 * puella bona ||rowspan=4 style="width:30px"| || (good girl, feminine singular nominative)
 * puellam bonam || (good girl, feminine singular accusative/object case)
 * puer bonus || (good boy, masculine singular nominative)
 * pueri boni || (good boys, masculine plural nominative)
 * }
 * pueri boni || (good boys, masculine plural nominative)
 * }
 * }

In Celtic languages, however, initial consonant lenition marks the adjective with a feminine singular noun, as in Irish:

 * {|border=0

 * buachaill maith ||rowspan=4 style="width:30px"| || (good boy, masculine)
 * girseach mhaith || (good girl, feminine)
 * }
 * }

Here, a distinction may be made between attributive and predicative usage. In English, adjectives never agree, whereas in French, they always agree. In German, they agree only when they are used attributively, and in Hungarian, they agree only when they are used predicatively:

 * {|border=0

 * The good (Ø) boys. ||rowspan=4 style="width:30px"| || The boys are good (Ø).
 * Les bons garçons. || Les garçons sont bons.
 * Die braven Jungen. || Die Jungen sind brav (Ø).
 * A jó (Ø) fiúk. || A fiúk jók.
 * }
 * A jó (Ø) fiúk. || A fiúk jók.
 * }
 * }

Semantics
Semanticist Barbara Partee classifies adjectives semantically as intersective, subsective, or nonsubsective, with nonsubsective adjectives being plain nonsubsective or privative.

 * An adjective is intersective if and only if the extension of its combination with a noun is equal to the intersection of its extension and that of the noun its modifying. For example, the adjective carnivorous is intersective, given the extension of carnivorous mammal is the intersection of the extensions of carnivorous and mammal (i.e., the set of all mammals who are carnivorous).
 * An adjective is subsective if and only if the extension of its combination with a noun is a subset of the extension of the noun. For example, the extension of skillful surgeon is a subset of the extension of surgeon, but it is not the intersection of that and the extension of skillful, as that would include (for example) incompetent surgeons who are skilled violinists. All intersective adjectives are subsective, but the term 'subsective' is sometimes used to refer to only those subsective adjectives which are not intersective.
 * An adjective is privative if and only if the extension of its combination with a noun is disjoint from the extension of the noun. For example, fake is privative because a fake cat is not a cat.
 * A plain nonsubsective adjective is an adjective that is not subsective or privative. For example, the word possible is this kind of adjective, as the extension of possible murderer overlaps with, but is not included in the extension of murderer (as some, but not all, possible murderers are murderers).

title: Adjective


text:
Adverb

An adverb is a word or an expression that generally modifies a verb, adjective, another adverb, determiner, clause, preposition, or sentence. Adverbs typically express manner, place, time, frequency, degree, level of certainty., answering questions such as how, in what way, when, where, to what extent. This is called the adverbial function and may be performed by single words (adverbs) or by multi-word adverbial phrases and adverbial clauses.

Adverbs are traditionally regarded as one of the parts of speech. Modern linguists note that the term adverb has come to be used as a kind of "catch-all" category, used to classify words with various types of syntactic behavior, not necessarily having much in common except that they do not fit into any of the other available categories (noun, adjective, preposition, etc.).

Functions
The English word adverb derives (through French) from Latin adverbium, from ad- ('to'), verbum ('word', 'verb'), and the nominal suffix -ium. The term implies that the principal function of adverbs is to act as modifiers of verbs or verb phrases. An adverb used in this way may provide information about the manner, place, time, frequency, certainty, or other circumstances of the activity denoted by the verb or verb phrase. Some examples:
 * She sang loudly (loudly modifies the verb sang, indicating the manner of singing)
 * We left it here (here modifies the verb phrase left it, indicating place)
 * I worked yesterday (yesterday modifies the verb worked, indicating time)
 * You often make mistakes (often modifies the verb phrase make mistakes, indicating frequency)
 * He undoubtedly did it (undoubtedly modifies the verb phrase did it, indicating certainty)

Adverbs can also be used as modifiers of adjectives, and of other adverbs, often to indicate degree. Examples:
 * You are quite right (the adverb quite modifies the adjective right)
 * She sang very loudly (the adverb very modifies another adverb – loudly)

They can also modify determiners, prepositional phrases, or whole clauses or sentences, as in the following examples: Adverbs thus perform a wide range of modifying functions. The major exception is the function of modifier of nouns, which is performed instead by adjectives (compare she sang loudly with her loud singing disturbed me; here the verb sang is modified by the adverb loudly, whereas the noun singing is modified by the adjective loud). However, because some adverbs and adjectives are homonyms, their respective functions are sometimes conflated: The word even in the first sentence is an adjective, since it is a prepositive modifier that modifies the noun numbers. The word "even" in the second sentence is a prepositive adverb that modifies the verb "drank."
 * I bought practically the only fruit (practically modifies the determiner the  in the noun phrase, "the only fruit" wherein only is an adjective)
 * She drove us almost to the station (almost modifies the prepositional phrase to the station)
 * Certainly we need to act (certainly modifies the sentence as a whole)
 * Even numbers are divisible by two
 * The camel even drank.

Although it is possible for an adverb to precede or to follow a noun or a noun phrase, the adverb nonetheless does not modify either in such cases, as in: In the first sentence, "Internationally" is a prepositive adverb that modifies the clause, "there is ..." In the second sentence, "internationally" is a postpositive adverb that modifies the clause, "There is ..." By contrast, the third sentence contains "international" as a prepositive adjective that modifies the noun, "shortage."
 * Internationally there is a shortage of protein for animal feeds
 * There is a shortage internationally of protein for animal feeds
 * There is an international shortage of protein for animal feeds

Adverbs can sometimes be used as predicative expressions; in English, this applies especially to adverbs of location:
 * Your seat is there.
 * Here is my boarding pass (wherein "boarding pass" is the subject and "here" is the predicate in a syntax that entails a subject-verb inversion).

When the function of an adverb is performed by an expression consisting of more than one word, it is called an adverbial phrase or adverbial clause, or simply an adverbial.

Formation and comparison
In English, adverbs of manner (answering the question how?) are often formed by adding -ly to adjectives, but flat adverbs (such as in drive fast, drive slow, and drive friendly) have the same form as the corresponding adjective. Other languages often have similar methods for deriving adverbs from adjectives (French, for example, uses the suffix -ment), or else use the same form for both adjectives and adverbs, as in German and Dutch, where for example schnell or snel, respectively, mean either "quick" or "quickly" depending on the context. Many other adverbs, however, are not related to adjectives in this way; they may be derived from other words or phrases, or may be single morphemes. Examples of such adverbs in English include here, there, together, yesterday, aboard, very, almost, etc.

Where the meaning permits, adverbs may undergo comparison, taking comparative and superlative forms. In English this is usually done by adding more and most before the adverb (more slowly, most slowly), although there are a few adverbs that take inflected forms, such as well, for which better and best are used.

For more information about the formation and use of adverbs in English, see English adverbs. For other languages, see below, and the articles on individual languages and their grammars.

As a "catch-all" category
Adverbs are considered a part of speech in traditional English grammar, and are still included as a part of speech in grammar taught in schools and used in dictionaries. However, modern grammarians recognize that words traditionally grouped together as adverbs serve a number of different functions. Some describe adverbs as a "catch-all" category that includes all words that do not belong to one of the other parts of speech.

A logical approach to dividing words into classes relies on recognizing which words can be used in a certain context. For example, the only type of word that can be inserted in the following template to form a grammatical sentence is a noun:
 * The _____ is red. (For example, "The hat is red".)

When this approach is taken, it is seen that adverbs fall into a number of different categories. For example, some adverbs can be used to modify an entire sentence, whereas others cannot. Even when a sentential adverb has other functions, the meaning is often not the same. For example, in the sentences She gave birth naturally and Naturally, she gave birth, the word naturally has different meanings: in the first sentence, as a verb-modifying adverb, it means "in a natural manner", while in the second sentence, as a sentential adverb, it means something like "of course".

Words like very afford another example. We can say Perry is very fast, but not Perry very won the race. These words can modify adjectives but not verbs. On the other hand, there are words like here and there that cannot modify adjectives. We can say The sock looks good there but not It is a there beautiful sock. The fact that many adverbs can be used in more than one of these functions can confuse the issue, and it may seem like splitting hairs to say that a single adverb is really two or more words that serve different functions. However, this distinction can be useful, especially when considering adverbs like naturally that have different meanings in their different functions. Rodney Huddleston distinguishes between a word and a lexicogrammatical-word.

Grammarians find difficulty categorizing negating words, such as the English not. Although traditionally listed as an adverb, this word does not behave grammatically like any other, and it probably should be placed in a class of its own.

In other languages

 * In Dutch adverbs have the basic form of their corresponding adjectives and are not inflected (though they sometimes can be compared).
 * In German the term Adverb is defined differently from its use in the English language. German adverbs form a group of uninflectable words (though a few can be compared). An English adverb which is derived from an adjective is arranged in German under the adjectives with adverbial use in the sentence. The others are also called adverbs in the German language.
 * In Scandinavian languages, adverbs are typically derived from adjectives by adding the suffix '-t', which makes it identical to the adjective's neuter form. Scandinavian adjectives, like English ones, are inflected in terms of comparison by adding '-ere'/'-are' (comparative) or '-est'/'-ast' (superlative). In inflected forms of adjectives, the '-t' is absent. Periphrastic comparison is also possible.
 * In most Romance languages, many adverbs are formed from adjectives (often the feminine form) by adding '-mente' (Portuguese, Spanish, Galician, Italian) or '-ment' (French, Catalan) (from Latin mens, mentis: mind, intelligence, or suffix -mentum, result or way of action), while other adverbs are single forms which are invariable. In Romanian, almost all adverbs are simply the masculine singular form of the corresponding adjective, one notable exception being bine ("well") / bun ("good"). However, there are some Romanian adverbs built from certain masculine singular nouns using the suffix "-ește", such as the following ones: băieț-ește (boyishly), tiner-ește (youthfully), bărbăt-ește (manly), frăț-ește (brotherly), etc.
 * Interlingua also forms adverbs by adding '-mente' to the adjective. If an adjective ends in c, the adverbial ending is '-amente'. A few short, invariable adverbs, such as ben ("well"), and mal ("badly"), are available and widely used.
 * In Esperanto, adverbs are not formed from adjectives but are made by adding '-e' directly to the word root. Thus, from bon are derived bone, "well", and bona, "good". See also: special Esperanto adverbs.
 * In Hungarian adverbs are formed from adjectives of any degree through the suffixes -ul/ül and -an/en depending on the adjective: szép (beautiful) → szépen (beautifully) or the comparative szebb (more beautiful) → szebben (more beautifully)
 * Modern Standard Arabic forms adverbs by adding the indefinite accusative ending '-an' to the root: kathiir-, "many", becomes kathiiran "much". However, Arabic often avoids adverbs by using a cognate accusative followed by an adjective.
 * Austronesian languages generally form comparative adverbs by repeating the root (as in WikiWiki) as with the plural noun.
 * Japanese forms adverbs from verbal adjectives by adding /ku/ (く) to the stem (haya- "swift" hayai "quick/early", hayakatta "was quick", hayaku "quickly") and from nominal adjectives by placing /ni/ (に) after the adjective instead of the copula /na/ (な) or /no/ (の) (rippa "splendid", rippa ni "splendidly"). The derivations are quite productive, but for a few adjectives, adverbs may not be derived.
 * In the Celtic languages, an adverbial form is often made by preceding the adjective with a preposition: go in Irish or gu in Scottish Gaelic, meaning 'until'. In Cornish, yn is used, meaning 'in'.
 * In Modern Greek, an adverb is most commonly made by adding the endings <-α> or <-ως> to the root of an adjective. Often, the adverbs formed from a common root using each of these endings have slightly different meanings. So, <τέλειος> (, meaning "perfect" and "complete") yields <τέλεια> (, "perfectly") and <τελείως> (, "completely"). Not all adjectives can be transformed into adverbs by using both endings. <Γρήγορος> (, "swift") becomes <γρήγορα> (, "swiftly"), but not normally *<γρηγόρως> (*). When the <-ως> ending is used to transform an adjective whose stress accent is on the third syllable from the end, such as <επίσημος> (, "official"), the corresponding adverb is accented on the second syllable from the end; compare <επίσημα> () and <επισήμως> (), which both mean "officially". There are also other endings with particular and restricted use as <-ί>, <-εί>, <-ιστί>, etc. For example, <ατιμωρητί> (, "with impunity") and <ασυζητητί> (, "indisputably"); <αυτολεξεί> ( "word for word") and <αυτοστιγμεί> (, "in no time"); <αγγλιστί> [ "in English (language)"] and <παπαγαλιστί> (, "by rote"); etc.
 * In Latvian, an adverb is formed from an adjective by changing the masculine or feminine adjective endings -s and -a to -i. "Labs", meaning "good", becomes "labi" for "well". Latvian adverbs have a particular use in expressions meaning "to speak" or "to understand" a language. Rather than use the noun meaning "Latvian/English/Russian", the adverb formed from these words is used. "Es runāju latviski/angliski/krieviski" means "I speak Latvian/English/Russian" or, literally, "I speak Latvianly/Englishly/Russianly". If a noun is required, the expression used means literally "language of the Latvians/English/Russians", "latviešu/angļu/krievu valoda".
 * In Russian, and analogously in Ukrainian and some other Slavic languages, most adverbs are formed by removing the adjectival suffixes "-ий" "-а" or "-е" from an adjective, and replacing them with the adverbial "-о". For example, in Ukrainian, "швидкий", "гарна", and "смачне" (fast, nice, tasty) become "швидко", "гарно", and "смачно" (quickly, nicely, tastily), while in Russian, "быстрый", "хороший" and "прекрасный" (quick, good, wonderful) become "быстро", "хорошо", "прекрасно" (quickly, well, wonderfully). Another wide group of adverbs are formed by gluing a preposition to an oblique case form. In Ukrainian, for example, (до onto)  +  (долу bottom) → (додолу downwards); (з off) + (далеку afar) → (здалеку  afar-off) . As well, adverbs are mostly placed before the verbs they modify: "Добрий син гарно співає." (A good son sings nicely/well). There is no specific word order in East Slavic languages.
 * In Korean, adverbs are commonly formed by replacing the -다 ending of the dictionary form of a descriptive verb with 게. So, 쉽다 (easy) becomes 쉽게 (easily). They are also formed by replacing the 하다 of some compound verbs with 히, e.g. 안녕하다 (peaceful) > 안녕히 (peacefully).
 * In Turkish, the same word usually serves as adjective and adverb: iyi bir kız ("a good girl"), iyi anlamak ("to understand well'').
 * In Chinese, adverbs are not a separate class. Adjectives become adverbs when they are marked by an adverbial suffix, for example 地 de（e.g., 孩子們快樂地唱歌 haizimen kuaile.de changge 'the children happily sing a song'), or when adjectives are preceded by a verbal suffix such as 得 dei (e.g., 她說漢語說得很好 ta shuo hanyu shuo.de henhao 'she speaks Chinese very well').
 * In Persian, many adjectives and adverbs have the same form such as "خوب", "سریع", "تند" so there is no obvious way to recognise them out of context. The only exceptions are Arabic adverbs with a "اً" suffix such as "ظاهراً" and "واقعاً".

title: Adverb