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Encyclopedia > Andesite
A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. Diameter of view is 8 cm.
A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. Diameter of view is 8 cm.

Andesite (pronounced /ˈændəsaɪt/) is an igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. The mineral assembly is typically dominated by plagioclase plus pyroxene and/or hornblende. Biotite, quartz, magnetite, sphene 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. Relative alkali and silica contents are illustrated in TAS diagrams. Image File history File links Amygdaloidal_andesite. ... Image File history File links Amygdaloidal_andesite. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... Zeolite The micro-porous molecular structure of a zeolite, ZSM-5 Zeolites (Greek, zein, to boil; lithos, a stone) are minerals that have a micro-porous structure. ... Volcanic rock in North America Plutonic rock in North America Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Ignimbrite is a deposit of a pyroclastic flow. ... Volcanic rock in North America Plutonic rock in North America Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... An aphanite is an igneous rock with a fine-grained structure. ... (For other meanings of Porphyr, see Porphyry) The baptismal font in the Cathedral of Magdeburg is made of rose porphyry from a site near Assuan, Egypt Porphyry is a very hard red, green or purple igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a... For other uses, see Mineral (disambiguation). ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... For other uses, see Quartz (disambiguation). ... Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Titanite or sphene is a calcium titanium nesosilicate mineral, CaTiSiO5. ... This article does not cite any references or sources. ... A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogic composition. ... The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali content and the silica content. ...


Classification of andesites may be refined according to the most abundant phenocryst. Example: hornblende-phyric andesite, if hornblende is the principal accessory mineral. Example of phenocrysts in rhomb porphyry from the Oslo rift area in Norway A phenocryst is a relatively large and usually conspicuous crystal formed in the mass of a porphyritic igneous rock. ...


Andesite can be considered as the extrusive equivalent to plutonic diorite. Andesites are characteristic of subduction tectonic environments in active oceanic margins, such as the western coast of South America. The name andesite is derived from the Andes mountain range. In geology an intrusion is usually a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. ... Categories: Mineral stubs | Igneous rocks ... Geometry of a subduction zone - insets to show accretionary prism and partial melting of hydrated asthenosphere. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... This article is about the mountain system in South America. ...

Contents

Genesis of andesite

Andesite is formed at accretionary plate margins. Intermediate volcanic rocks are created via several processes:

  1. Dehydration melting of peridotite and fractional crystallization
  2. Melting of subducted slab containing sediments
  3. Magma mixing between felsic rhyolitic and mafic basaltic magmas in an intermediate reservoir prior to emplacement or eruption.

In chemistry, Fractional Crystallization is a method of refining substances based on differences in soluability. ... This page is about a volcanic rock. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ...

Via fractional crystallisation

Andesitic magma in island arc regions (i.e. active oceanic margins) comes from the interplay of the subducting plate and the mantle wedge, the part of the overriding plate above the subducted plate. Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... An island arc is a type of archipelago formed by plate tectonics as one oceanic tectonic plate subducts under another and produces magma. ...


Water in the subducted oceanic crust 'boils off' from the slab by dehydration of hydrated minerals such as amphibole, zeolites, chlorite etc, which are formed in oceanic crust during hydrothermal circulation at the mid-ocean-ridge spreading centre. As these minerals are subjected to Barrovian Facies Sequence or Franciscan Facies Sequence metamorphism during subduction, they metamorphose to more stable, dehydrated forms, releasing water and volatile elements into the mantle wedge. For the logical fallacy, see Amphibology. ... Zeolite The micro-porous molecular structure of a zeolite, ZSM-5 Zeolites (Greek, zein, to boil; lithos, a stone) are minerals that have a micro-porous structure. ... Chlorite is a group of phyllosilicate minerals often classified as clays. ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ... Greenschist is a general field petrologic term applied to metamorphically altered mafic volcanic rock. ... Blueschist is a rock that forms by the metamorphism of sodium-rich basic rocks at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to 400 degrees Celsius (cool by metamorphic standards). ...


The slab itself, or the overlying mantle wedge, may melt. Melting subducted slab components have a sediment component from the subducted plate, which can be detected by increased lead and barium in the melts which are produced. The water and initial tylerisstupid slab melts rise into the mantle wedge, prompting melting of the peridotite to produce a basaltic melt with a distinct subduction signature in its trace element composition (eg, shoshonite, adakite). This article is about the metal. ... For other uses, see Barium (disambiguation). ... Peridotite xenolith from San Carlos, southwestern United States. ... Adakite is a petrologic term for a volcanic or intrusive igneous rock that forms by melting of a subducting slab of oceanic crust basalt. ...


On its way to the surface, the melt stalls and cools, enabling the fractional crystallization of silica poor minerals, thus raising the silica content of the remaining melt and resulting in andesitic magma. The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ...


Via magma mixing

Basaltic magma may also mix with rhyolitic magma. This usually occurs in continental arc areas such as the Andes, where the high geothermal gradient above the subducted plate, and hydrothermal flows within the mantle wedge may create an underplate of softened, partially molten continental crust of intermediate or felsic composition. Basaltic magmas intruded into this anomalously hot zone will prompt partial melting of the crust, and may mix with these melts to produce intermediate compositions, typically andesite to trachyte in composition. This article is about the mountain system in South America. ... penis, hahaha big long penis. ...


Alternatively, the basaltic melt may heat up the overlying arc, prompting partial melting, and may even assimilate sediments, previous volcanic rocks, etcetera, whilst undergoing fractional crystallisation. These rocks are subordinate due to the difficulty in assimilating sufficient cold material by magmas without cooling to a degree that they become immobile.


Ultimately, the resultant composition of andesite and intermediate magmas is the result of fractional crystallisation, assimilation, partial melting cbnvcnvcnnbvcnbvc and contaminaton by the subducted slab. These may take considerable effort to resolve the individual components.


See also

This page is intended as a list of all rock types. ... The thickness of the Earths crust (km). ... Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ... Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i. ... For other uses, see granite (disambiguation). ... In chemistry, Fractional Crystallization is a method of refining substances based on differences in soluability. ... The Andesite Line is the most significant regional distinction in the Pacific. ... Porphyry (Greek Πορφύριος purple-clad) may refer to: Porphyry of Tyros (c. ...

External links

References


  Results from FactBites:
 
Andesite - LoveToKnow 1911 (1114 words)
ANDESITE, a name first applied by C. von Buch to a series of lavas investigated by him from the Andes, which has passed into general acceptance as the designation of a great family of rocks playing an important part in the geology of most of the volcanic areas of the globe.
The andesites have mostly a porphyritic structure, and the larger felspars and ferro-magnesian minerals are often visible to the naked eye, lying in a finer groundmass, usually crystalline, but sometimes to a large extent vitreous.
Garnet and sapphire have also been found in andesites, and perhaps have the same signification; a rose-red variety of epidote (withamite) is known as a secondary product in certain andesites (Glencoe, Scotland), and the famous red porphyry (porfido rosso) of the ancients is a rock of this type.
Rocks and Minerals Tour: Envi Sci Dept, UVA (201 words)
Andesite is an igneous rock, which means it was formed when hot, melted rock and a mixture of crystals deep in the earth cooled and become a solid.
Andesite is named for the Andes Mountains, which where created due to an andesitic lava flow.
Texture of andesite is often porphyritic, which means that larger grains are set in with fine or glassy grains in a matrix pattern.
  More results at FactBites »

 
 

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