NationMaster - Encyclopedia: Amphibolite

Amphibolite (IPA: /æmˈfɪbəlɑɪt/, /amˈfɪbəlʌɪt/) is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks rock composed primarily of hornblende amphibole is a hornblendite, which are usually crystal cumulates. Rocks with >90% amphibole which have a feldspar groundmass may be a lamprophyre. Image File history File links Metadata Size of this preview: 800 Ã— 600 pixelsFull resolution (2816 Ã— 2112 pixel, file size: 2 MB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Metadata Size of this preview: 800 Ã— 600 pixelsFull resolution (2816 Ã— 2112 pixel, file size: 2 MB, MIME type: image/jpeg) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Articles with similar titles include the NATO phonetic alphabet, which has also informally been called the â€œInternational Phonetic Alphabetâ€. For information on how to read IPA transcriptions of English words, see IPA chart for English. ... This balancing rock, Steamboat Rock stands in Garden of the Gods park in Colorado Springs, CO The rocky side of a mountain creek near OrosÃ, Costa Rica. ... For the logical fallacy, see Amphibology. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks form when rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Hornblendite is a plutonic rock consisting mainly of the amphibole hornblende. ... Lamprophyres (Greek Lampros, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals) are a group of rocks containing phenocrysts, usually of biotite and hornblende (with bright cleavage surfaces), often also of olivine and augite, but not of feldspar. ...

Amphibolite is a gouping of rocks composed mainly of amphibole (as hornblende) and plagioclase feldspars, with little or no quartz. It is typically dark-colored and heavy, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance. For the logical fallacy, see Amphibology. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... This article does not cite any references or sources. ... Quartz is one of the most common minerals in the Earths continental crust. ...

Amphibolites need not be derived from metamorphosed mafic rocks. Because metamorphism creates minerals based entirely upon the chemistry of the protolith, certain 'dirty marls' and volcanic sediments may actually metamorphose to an amphibolite assemblage. Deposits containing dolomite and siderite also readily yield amphibolites (tremolite-schists, grunerite-schists, and others) especially where there has been a certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalts create ortho-amphibolites and other chemically appropriate lithologies create para-amphibolites. Marls are calcium carbonate or lime rich muds or mudstones which contain variable amounts of clays and calcite or aragonite. ... Dolomite crystals from Touissite, Morocco Dolomite is the name of both a carbonate rock and a mineral consisting of calcium magnesium carbonate (formula: CaMg(CO3)2) found in crystals. ... Siderite is also the name of a type of iron meteorite. ...

Tremolite, while it is a metamorphic amphibole, is derived most usually from highly metamorphosed ultramafic rocks, and thus tremolite-talc schists are not generally considered as 'amphibolites', because it is abundantly clear that one could just as easily say 'ultramafic schist'. Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ...

Because hornblende, as a mineral, is essentially a mineralogical 'garbage bin' and is stable across a very wide range of compositions and chemistries, as well as temperature and pressure conditions, it is suggested that the reader make use of the entries on amphibole chemistry. Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... For the logical fallacy, see Amphibology. ...

Ortho-amphibolites vs. para-amphibolites

Metamorphic rocks composed primarily of amphibole, albite, with subordinate epidote, zoisite, chlorite, quartz, sphene, and accessory leucoxene, ilmenite and magnetite which have a protolith of an igneous rock are known as Orthoamphibolites. For the logical fallacy, see Amphibology. ... Albite Albite is an alkali feldspar mineral. ... Epidote from Slovakia Epidote is a calcium aluminium iron sorosilicate mineral, Ca2(Al, Fe)3(SiO4)3(OH), crystallizing in the monoclinic system. ... This article is about the mineral named zoisite. ... The chlorite ion This discusses some chlorine compounds. ... Quartz is one of the most common minerals in the Earths continental crust. ... Titanite or sphene is a calcium titanium nesosilicate mineral, CaTiSiO5. ... Leucoxene is a finely granular yellow to brown alteration product of titanium minerals. ... Ilmenite is a weakly magnetic iron-black or steel-gray mineral found in metamorphic and igneous rocks. ... // Headline text Magnetite is a ferrimagnetic mineral form of iron(II,III) oxide, with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Protolith refers to the precursor rock of a given lithology. ...

Para-amphibolites will generally have the same equilibrium mineral assemblage as orthoamphibolites, with more biotite, and may include more quartz, albite, and depending on the protolith, more calcite/aragonite and wollastonite. Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... Aragonite Aragonite is a polymorph of the mineral calcite, both having the chemical composition CaCO3. ... Wollastonite is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. ...

Often the easiest way to determine the true nature of an amphibolite is to inspect its field relationships; especially whether it is interfingered with other sediments, especially greywackes and other poorly sorted sediments. If the amphibolite appears to transgress apparent protolith bedding surfaces it is an ortho-amphibolite, as this suggests it was a dyke. Picking a sill and thin metamorphosed lava flows may be more troublesome. Greywacke (German grauwacke, signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly-sorted, angular grains of quartz, feldspar, and small rock fragments set in a compact, clay-fine matrix. ... A dike in geology refers to a tabular intrusive igneous body. ... In geology, a sill is a tabular, often horizontal mass of igneous rock that has been intruded laterally between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ...

Thereafter, whole rock geochemistry will suitably identify ortho- from para-amphibolites.

The word metabasalt was thus coined, largely to avoid the confusion between ortho-amphibolites and para-amphibolites. While not a true metamorphic rock name, as it infers an origin, it is a useful term.

Amphibolite Facies

Amphibolites define a particular set of temperature and pressure conditions known as the Amphibolite Facies. However, caution must be applied here before embarking on metamorphic mapping based on amphibolites alone.

Firstly, for an (ortho)amphibolite to be classed as a metamorphic amphibolite, it must be certain that the amphibole in the rock is a prograde metamorphic product, and not a retrograde metamorphic product. For instance, actinolite amphibole is a common product of retrograde metamorphism of basalts at (upper) greenschist facies conditions. Often, this will take on the crystal form and habit of the original protolith assemblage; actinolite pseudomorphically replacing pyroxene is an indication that the amphibolite may not represent a peak metamorphic grade in the amphibolite facies. Actinolite schists are often the result of hydrothermal alteration or metasomatism, and thus may not, necessarily, be a good indicator of metamorphic conditions when taken in isolation. This article is about retrograde motion. ... Well-cleaved, dark, fine-grained chlorite-actinolite metadiabase intrudes light granitic gneiss Actinolite is an inosilicate mineral with the chemical formula Ca2(MgFe)5Si8O22(OH)2 // Mineralogy Actinolite is an intermediate member in a series between tremolite (Mg-rich) and ferro-actinolite (Fe-rich). ... Greenschist is a general field petrologic term applied to metamorphically altered mafic volcanic rock. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ...

Secondly, the microstructure and crystal size of the rock must be appropriate. Amphibolite Facies conditions are experienced at temperatures in excess of 500 °c and pressures in excess of 1.2GPa, well within the ductile deformation field. You should expect to find a gneissic texture somewhere nearby, if not mylonite zones, foliations and ductile behaviour, including stretching lineations. Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. ... Mylonite is a fine-grained, compact rock without cleavage or crystals. ... Foliation is any penetrative planar fabric present in rocks. ...

While it is not impossible to find remnant protolith mineralogy, this is rare. More common is to find phenocrysts of pyroxene, olivine, plagioclase and even magmatic amphibole such as pargasite rhombohedra, pseudomorphed by hornblende amphibole. Original magmatic textures, especially crude magmatic layering in layered intrusions, is often preserved, though this may require imaginative and persistent study. 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. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... It has been suggested that this article or section be merged with Ultramafic intrusion. ...

Amphibolite facies equilibrium mineral assemblages of various protolith rock types are laid out below;

Amphibolite facies is usually a product of Barrovian Facies Sequence or advanced Abukuma Facies Sequence metamorphic trajectories. Amphibolite facies is a result of continuing burial and thermal heating after Greenschist facies is exceeded.
Further burial and metamorphic compression (but little extra heat) will lead to Granulite Facies metamorphism; it is rare to see much more advanced heating because the majority of rocks begin melting in excess of 650 to 700 degrees celsius in the presence of water. In dry rocks, however, additional heat (and burial) may result in Eclogite Facies conditions. Greenschist is a general field petrologic term applied to metamorphically altered mafic volcanic rock. ... The chlorite ion This discusses some chlorine compounds. ... Anthophyllite is an amphibole mineral: (Mg, Fe)7Si8O22(OH)2, magnesium iron inosilicate hydroxide. ... A sample of tremolite Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2Mg5Si8O22(OH)2. ... It has been suggested that Asbestos fibers be merged into this article or section. ... Talc (derived from the Persian via Arabic talq) is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Wollastonite is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Orthoclase (KAlSi3O8) is an important tectosilicate mineral, which forms igneous rock. ... Staurolite Staurolite is a red brown to black mostly opaque nesosilicate mineral with a white streak. ... Sillimanite: Biotite gneiss (Mesozoic and Paleozoic) Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. ... Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered mafic volcanic rock. ... A sample of granulite rock Granulites are metamorphic rocks that have experienced high temperatures of metamorphism. ... Eclogite piece with a garnet (red) and omphacite (greyish-green) groundmass. ...

Uralite

Uralites are particular hydrothermally altered pyroxenites, which during autogenic hydrothermal circulation, the primary mineralogy of pyroxene and plagioclase, etc have altered to actinolite and saussurite (albite + epidote). The texture is distinctive, the pyroxene altered to fuzzy, radially arranged actinolite pseudomorphically after pyroxene, and saussuritised plagioclase. Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Well-cleaved, dark, fine-grained chlorite-actinolite metadiabase intrudes light granitic gneiss Actinolite is an inosilicate mineral with the chemical formula Ca2(MgFe)5Si8O22(OH)2 // Mineralogy Actinolite is an intermediate member in a series between tremolite (Mg-rich) and ferro-actinolite (Fe-rich). ...

Epidiorite

The archaic term epidiorite is sometimes used to refer to a metamorphosed ortho-amphibolite with a protolith of diorite, gabbro or other mafic intrusive rock. In epidiorite the original clinopyroxene (most often augite) has been replaced by the fibrous amphibole uralite. Protolith refers to the precursor rock of a given lithology. ... Categories: Mineral stubs | Igneous rocks ... Gabbro specimen. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Augite is a single chain inosilicate mineral described chemically as (Ca,Mg,Fe)SiO3 or calcium magnesium iron silicate. ... For the logical fallacy, see Amphibology. ...

Contents

Ortho-amphibolites vs. para-amphibolites

Amphibolite Facies

Uralite

Epidiorite

See also

Uses

References

Contents

Ortho-amphibolites vs. para-amphibolites GA_googleFillSlot("encyclopedia_square");

Amphibolite Facies

Uralite

Epidiorite

See also

Uses

References

Ortho-amphibolites vs. para-amphibolites