Andesite: The specimen shown is about two inches five centimeters across and has a porphyritic texture. Igneous rock composition chart: This chart shows that andesite is typically composed of plagioclase, amphiboles, and micas; sometimes with minor amounts of pyroxenes, quartz, or orthoclase. Andesite is the name used for a family of fine-grained, extrusive igneous rocks that are usually light to dark gray in color.
They often weather to various shades of brown, and these specimens must be broken for proper examination. Andesite is rich in plagioclase feldspar minerals and may contain biotitepyroxenesor amphiboles.
Andesite usually does not contain quartz or olivine. Andesite is typically found in lava flows produced by stratovolcanoes. Because these lavas cooled rapidly at the surface, they are generally composed of small crystals. The mineral grains are usually so small that they cannot be seen without the use of a magnifying device.
Some specimens that cooled rapidly contain a significant amount of glass, while others that formed from gas-charged lavas have a vesicular or amygdaloidal texture. Stratovolcanoes: Pavlof Volcano right and Pavlof Sister Volcano left are a pair of symmetrical stratovolcanoes built of andesite flows and tephra on the Alaska Peninsula.
Pavlof Volcano is one of the most active volcanoes in Alaska. Photo by T. Miller, United States Geological Survey. Andesite and diorite are common rocks of the continental crust above subduction zones.
They generally form after an oceanic plate melts during its descent into the subduction zone to produce a source of magma. Diorite is a coarse-grained igneous rock that forms when the magma did not erupt, but instead slowly crystallized within Earth's crust. Andesite is a fine-grained rock that formed when the magma erupted onto the surface and crystallized quickly.
Andesite and diorite have a composition that is intermediate between basalt and granite. This is because their parent magmas formed from the partial melting of a basaltic oceanic plate. This magma may have received a granitic contribution by melting granitic rocks as it ascended or mixed with granitic magma. Andesite derives its name from the Andes Mountains of South America. In the Andes it occurs as lava flows interbedded with ash and tuff deposits on the steep flanks of stratovolcanoes.
Andesite can also form away from the subduction zone environment. For example, it can form at ocean ridges and oceanic hot spots from partial melting of basaltic rocks. It can also form during eruptions at continental plate interiors where deep-source magma melts continental crust or mixes with continental magmas.
There are many other environments where andesite might form.Andesine is a silicate mineral, and it was named after its original occurrence in the Andes Mountains of South America.
It is a member of the plagioclase feldspar solid solution series. The formula may be written as Na 0. Andesine belongs to the Plagioclase Feldspar group, an isomorphous solid solution series.
Albite is one member, containing sodium and no calcium. The other end member, Anorthite, contains calcium and no sodium. Andesine is an intermediary member of this series. Andesine is considered by some authorities as a variety of Albite rather than a separate mineral. Andesine is the primary feldspar constituent of the igneous rock Andesite. The plagioclase feldspars are a continuous solid solution series and as such the accurate identification of individual members requires detailed optical study, chemical analysis or density measurements.
Refractive indices and specific gravity increase directly with the calcium content. It is sometimes used as a gemstone.
The name is for the Andes due to its abundance in the andesite lavas in those mountains. It is mostly found in magmatic and metamorphic environment. It typically occurs in metamorphic rocks of granulite, usually showing antiperthite property. It occurs in the form of intermediate igneous rocks such as Diorite, Andesite and Syenite. This substance is also found as detrital grains in sedimentary rocks.
This chemical is closely related with Quartz, Potassium Feldspar and Magnetite. A fairly new gemstone shrouded in mystery, andesine is believed to have been discovered in the Congo near the Nyaragongo Volcano sometime in Andesine was originally traded without disclosure of color enhancements. Much of what was originally introduced to the gemstone market as andesine is not truly andesine and is actually enhanced labradorite, a fellow plagioclase feldspar.
Andesine has a faint metallic schiller called labradorescence and exhibits a range of color known as pleochroism. Andesine has a lovely red, reddish pink, and orange-pink color. This pretty color gave it a unique position as a new gemstone, because can rival the color of other more valuable red gemstones.
However, it is still soft for a gemstone, and it is prone to cracks from pressure. A few examples of Andesine may even exhibit a color-changing effect in different lighting.Andesites occur mainly as surface deposits and, to a lesser extent, as dikes and small plugs. Many of the deposits are not normal lava flows but rather flow breccias, mudflows, tuffs, and other fragmental rocks; the peperino near Rome and the trass of the Eifel district in Germany are examples.
Not only the Andes, where the name was first applied to a series of lavas, but most of the cordillera parallel mountain chains of Central and North America consist largely of andesites. The same rock type occurs in abundance in volcanoes along practically the entire margin of the Pacific Basin.
Andesite most commonly denotes fine-grained, usually porphyritic rocks; in composition these correspond roughly to the intrusive igneous rock diorite and consist essentially of andesine a plagioclase feldspar and one or more ferromagnesian minerals, such as pyroxene or biotite.
Smaller amounts of sanidine, a potassium-rich feldsparmay be present. The larger crystals of feldspar and ferromagnesian minerals are often visible to the naked eye; they lie in a finer groundmass, usually crystalline, but sometimes glassy. There are three subdivisions of this rock family: the quartz-bearing andesites, or dacitessometimes considered to be a separate family; the hornblende- and biotite-andesites; and the pyroxene-andesites.
The dacites q. The hornblende- and biotite-andesites are comparatively rich in feldspar and are usually pale pink, yellow, or gray. Pyroxene-andesites are the commonest type of andesite and occur in amounts comparable to basalt. They are darker, denser, more basic rocks. Andesite Article Media Additional Info. Print Cite.
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The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree See Article History. Learn More in these related Britannica articles:. Rhyolite and andesite lavas were extruded in the area of the English Mendip Hills during Wenlock time. Basalts, rhyolites, and porphyritic andesites from the Newbery Volcanics in northeastern Massachusetts were formed during the Pridoli Epoch.
Rhyolitic and andesitic flows of Silurian age also are known in the…. The andesite formations of the Karancs and the basalt formations of the Medves stand out on the northern frontier.
The rivers…. History at your fingertips. Sign up here to see what happened On This Dayevery day in your inbox! Email address. By signing up, you agree to our Privacy Notice. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox.Diorite is a gray, coarse-grained plutonic rock. Diorite consists mainly of sodium-rich plagioclase and one or more mafic minerals such as biotite, hornblende, or pyroxene.
It is the coarse-grained equivalent of andesite. Diorite may contain small amounts of quartz, microcline, and olivine. Zircon, apatite, titanite, magnetite, ilmenite, and sulfides occur as accessory minerals.
The presence of sodium-rich feldspar, oligoclase or andesine, in contrast to calcium-rich plagioclase, labradorite or bytownite, is the main distinction between diorite and gabbro.
The extrusive volcanic equivalent of diorite is andesite. Partial melting of the oceanic plate produces a basaltic magma that rises and intrudes the granitic rock of the continental plate. There, the basaltic magma mixes with granitic magmas or melts granitic rock as it ascends through the continental plate. This produces a melt that is intermediate in composition between basalt and granite. Diorites may be associated with either granite or gabbro intrusions, into which they may subtly merge.
Properties and Uses of Andesite Rock
Diorite results from the partial melting of a mafic rock above a subduction zone. It is commonly produced in volcanic arcs, and in cordilleran mountain building, such as in the Andes Mountains, as large batholiths. The extrusive volcanic equivalent rock type is andesite. Many diorites are truly igneous, having crystallized from molten material magma.
Diorite occurs in small bodies such as sills, which are tabular bodies inserted while molten between other rocks, dikes tabular bodies injected in fissuresstocks bodies intruded upwardor as more irregular masses associated with gabbro and batholiths huge bodies of granodiorite and granite.
An orbicular variety found in Corsica is called corsite. Diorite properties are essential when it comes to identification of rocks. The study of properties of Diorite rock is done by Mineralogists to determine the identity of rock. Diorite is Medium to Coarse Grained. As compared to other rocks, Diorite is more porous and its density is 2.
Get to know more about physical properties of Diorite and thermal properties of Diorite. The hardness of Diorite is whereas its compressive strength is Streak is the color of rock when it is crushed or powdered. The streak of Diorite is bluish black whereas its fracture is not available. Luster of Diorite is the interaction of light with the surface of Diorite. Luster of Diorite is shiny. Diorite cleavage is not available.
The specific gravity of Diorite is 2. Diorite is opaque in nature whereas its toughness is 2. Diorite is used as a base material in the construction of roads, buildings, and parking areas. It is also used as a drainage stone and for erosion control. In the dimension stone industry, diorite is often cut into facing stone, tile, ashlars, blocking, pavers, curbing, and a variety of dimension stone products.
These are used as construction stone, or polished and used as architectural stone. Diorite was used as a structural stone by the Inca and Mayan civilizations of South America and by many ancient civilizations in the Middle East. Diorite Definition Diorite is a gray, coarse-grained plutonic rock. Occurrences and properties of Diorite Many diorites are truly igneous, having crystallized from molten material magma.
All Rights Reserved.Andesine is a silicate mineral, a member of the plagioclase feldspar solid solution series. It is a red feldspar gemstone, sometimes with greenish hints and a slight labradorescent effect. The plagioclase feldspars are a continuous solid solution series and as such the accurate identification of individual members requires detailed optical study, chemical analysis or density measurements. Andesine was first described in as an occurrence in the Marmato mine, Colombia.
It is named after the Andes mountains of South America. It is found in a range of colors, from red, honey-red to orange, yellow, champagne and green.
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Refractive indices and specific gravity increase directly with calcium content. After some controversy, these gemstones were subsequently discovered to have been artificially-colored. Andesine occurs in intermediate igneous rocks such as diorite, syenite, and andesite.
It characteristically occurs in metamorphic rocks of granulite to amphibolite facies commonly exhibiting antiperthite texture. It also occurs as detrital grains in sedimentary rocks. It is commonly associated with quartz, potassium feldspar, biotite, hornblende, and magnetite.
Information Source:. All Rights Reserved.Major minerals: plagioclase often andesine and pyroxene or hornblende. In a general sense, it is the intermediate type between basalt and rhyolite. It is fine-grained aphanitic to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende.
Andesite is the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is andesitic.
The name andesite is derived from the Andes mountain range, where this rock type is found in abundance. Andesite is an aphanitic fine-grained igneous rock that is intermediate in its content of silica and low in alkali metals. This places andesite in the O2 field of the TAS classification.
Andesite is usually light to dark gray in colour, due to its content of hornblende or pyroxene minerals. Darker andesite can be difficult to distinguish from basalt, but a common rule of thumbused away from the laboratory, is that andesite has a color index less than The plagioclase in andesite varies widely in sodium content, from anorthite to oligoclasebut is typically andesine.
The pyroxene minerals that may be present include augitepigeoniteor orthopyroxene. Magnetitezirconapatiteilmenitebiotiteand garnet are common accessory minerals. Classification of andesites may be refined according to the most abundant phenocryst. Example: hornblende-phyric andesiteif hornblende is the principal accessory mineral. Andesite is usually porphyriticcontaining larger crystals phenocrysts of plagioclase formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained matrix.
Phenocrysts of pyroxene or hornblende are also common. Andesite is typically formed at convergent plate margins but may also occur in other tectonic settings. Magmatism in island arc regions comes from the interplay of the subducting plate and the mantle wedgethe wedge-shaped region between the subducting and overriding plates. During subduction, the subducted oceanic crust is submitted to increasing pressure and temperature, leading to metamorphism.
Hydrous minerals such as amphibolezeoliteschlorite etc. Fluxing water into the wedge lowers the solidus of the mantle material and causes partial melting. Melts generated in the mantle wedge are of basaltic composition, but they have a distinctive enrichment of soluble elements e.
Although there is evidence to suggest that the subducting oceanic crust may also melt during this process, the relative contribution of the three components crust, sediment, and wedge to the generated basalts is still a matter of debate.Andesite is an extrusive igneous rock that has a porphyritic texture.
This rock is formed from molten magma, which has medium viscosity. Read this ScienceStruck article to know the facts, origin, formation, and properties of andesite rocks. The amount of silica contained in any rock determines its chemical composition.
Geologists use this measure to identify rocks and understand their characteristics. While granite is known to be rich and basalt or rhyolite to be poor in their silica content, andesite rock is said to be having silica content, intermediate to these rocks. Would you like to write for us? Well, we're looking for good writers who want to spread the word.
Get in touch with us and we'll talk These rocks are formed due to the constant subduction processes that lead to pushing of tectonic plates downward along the continental margins. Let us now understand the process of formation of andesite rocks. At times, magma crystallizes into rocks and certain minerals get removed from the rock once the process of crystallization is over.
This after a certain point of time results in the formation of andesite. In some instances, magma in the molten form moves in the upward direction towards the predominant crust. When molten magma comes in contact with the crustal portion, it tends to melt it. The partial melting of the crust leads to the creation of andesitic magma. The magma that is generated from the above two sources fuses to form these types of rocks.
The rock derives its name from Andes mountain ranges, which possess a large number of andesite rocks.
Besides this mountain range, the Cordillera mountain range of North and Central America houses these rocks too. Furthermore, this rock was also found in two space meteorites in the year in the Graves Nunatak Icefield during a meteorite search. Other examples can be peperino volcanic tuff located at Rome Italyor the trass volcanic tuff located at Eifel district Germany.
It is used as a filler or sometimes added as a constituent to various compounds.