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Amphibolite
Amphibolite

Amphibolite (pronounced /æmˈfɪbəlaɪt/) is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are usually crystal cumulates. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Hornblendite is a Plutonic rock consisting mainly of the Amphibole Hornblende. Rocks with >90% amphibole which have a feldspar groundmass may be a lamprophyre. Lamprophyres ( Greek λαµπρός (lamprós = "bright" and φύρω (phýro = to mix are uncommon small volume ultrapotassic Igneous rocks

Amphibolite is a grouping of rocks composed mainly of amphibole (as hornblende) and plagioclase feldspars, with little or no quartz. Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 Hornblende is a complex inosilicate series of Minerals Hornblende is not a recognized mineral in its own right but the name is used as a general or field term to Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family Feldspar is the name of a group of rock-forming Minerals which make up as much as 60% of the Earth 's crust. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in 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.

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. Marl or Marlstone is a Calcium carbonate or lime -rich mud or Mudstone which contains variable amounts of Clays and Aragonite 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. Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed Siderite is also the name of a type of Iron Meteorite. ---- Siderite is a Mineral composed of Iron Carbonate Fe[[carbon Metamorphosed basalts create ortho-amphibolites and other chemically appropriate lithologies create para-amphibolites.

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 (also referred to as ultrabasic) rocks are igneous and meta -igneous rocks with very low Silica content (less than 45% generally

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. Hornblende is a complex inosilicate series of Minerals Hornblende is not a recognized mineral in its own right but the name is used as a general or field term to Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4

Contents

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. Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 Albite is a plagioclase Feldspar Mineral. It is the sodium endmember of the Plagioclase Solid solution series Epidote is a Calcium Aluminium Iron sorosilicate Mineral, Ca2Al2(Fe3+Al(SiO4(Si2O7O(OH This article is about the mineral named zoisite For the Sailor Moon character see Shitennou. This discusses some chlorine compounds Chlorite is also a type of mineral see Chlorite group. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Titanite or sphene is a Calcium Titanium nesosilicate Mineral, Ca[[titanium Ti]] Si[[oxygen O]]5 Leucoxene is a fine Granular alteration product of Titanium Minerals It varies in color from yellow to brown Ilmenite is a weakly magnetic titanium-iron oxide Mineral which is iron-black or steel-gray Magnetite is not to be confused with Magnesite or Maghemite. Magnetite is a ferrimagnetic Mineral with chemical Protolith refers to the precursor Lithology of a Metamorphic rock

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. Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 Aragonite is a Carbonate mineral, one of the two common naturally occurring polymorphs of Calcium carbonate, Ca[[carbon C]] O 3

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. Greywacke ( German grauwacke, signifying a grey earthy rock is a variety of Sandstone generally characterized by its hardness dark color and poorly-sorted If the amphibolite appears to transgress apparent protolith bedding surfaces it is an ortho-amphibolite, as this suggests it was a dyke. A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar Picking a sill and thin metamorphosed lava flows may be more troublesome. In Geology, a sill is a tabular Pluton that has intruded between older layers of Sedimentary rock, beds of Volcanic Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures

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. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. For instance, actinolite amphibole is a common product of retrograde metamorphism of basalts at (upper) greenschist facies conditions. For the community in Canada see Actinolite Ontario. For the Sailor Moon character Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered Mafic Volcanic rock 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. The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. 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. Hydrothermal circulation in its most general sense is the circulation of hot water 'hydros' in the Greek meaning water and 'thermos' meaning heat

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. 2 GPa, 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 (ˈnaɪs is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally Mylonite is a fine-grained compact rock produced by dynamic crystallization of the constituent minerals resulting in a Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic

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. A phenocryst is a relatively large and usually conspicuous Crystal distinctly larger than the grains of the rock groundmass of a Porphyritic Igneous The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family Hornblende is a complex inosilicate series of Minerals Hornblende is not a recognized mineral in its own right but the name is used as a general or field term to Original magmatic textures, especially crude magmatic layering in layered intrusions, is often preserved, though this may require imaginative and persistent study. Ultramafic to mafic layered intrusions are found in typically ancient Cratons and are rare but worldwide in distribution

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. Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered Mafic Volcanic rock This discusses some chlorine compounds Chlorite is also a type of mineral see Chlorite group. Anthophyllite is an Amphibole Mineral: (Mg Fe7Si8O22(OH2 Magnesium Iron inosilicate Tremolite is a member of the Amphibole group of Silicate minerals with composition Ca 2 Mg 5 Si 8 Asbestos is a group of Minerals with long thin fibrous Crystals The word "asbestos" (῾ἀσβεστος is derived from a Greek adjective Talc (derived from the Persian via Arabic talq) is a Mineral composed of Hydrated Magnesium Silicate with The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg Physical properties Orthoclase crystallizes in the Monoclinic crystal system Staurolite is a red brown to black mostly opaque nesosilicate Mineral with a white streak Sillimanite also called Bucholzite is an alumino-silicate Mineral with the Chemical formula Al2SiO5 Amphibolite facies is a result of continuing burial and thermal heating after Greenschist facies is exceeded. Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered Mafic Volcanic rock
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. Granulites are fine to medium–grained Metamorphic rocks that have experienced high Temperatures of metamorphism composed mainly of Feldspars sometimes associated In dry rocks, however, additional heat (and burial) may result in Eclogite Facies conditions. Eclogite (ˈɛklədʒaɪt is a coarse-grained Mafic ( Basaltic in composition Metamorphic rock.

Uralite

Uralites are particular hydrothermally altered pyroxenites; during autogenic hydrothermal circulation their primary mineralogy of pyroxene and plagioclase, etc. The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family has altered to actinolite and saussurite (albite + epidote). For the community in Canada see Actinolite Ontario. For the Sailor Moon character The texture is distinctive, the pyroxene altered to fuzzy, radially arranged actinolite pseudomorphically after pyroxene, and saussuritised plagioclase.

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. Protolith refers to the precursor Lithology of a Metamorphic rock Diorite (ˈdaɪəraɪt is a grey to dark grey intermediate intrusive Igneous rock composed principally of Plagioclase Feldspar (typically Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. In epidiorite the original clinopyroxene (most often augite) has been replaced by the fibrous amphibole uralite. The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. Augite is a single chain inosilicate Mineral described chemically as (CaMgFeSiO3 or Calcium Magnesium Iron Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4

See also

Uses

Amphibolite was a favourite material for the production of adzes (shoe-last-celts) in the central European early Neolithic (Linearbandkeramic and Rössen cultures). Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock This page is intended as a list of all rock types A Amphibolite Andesite Anorthosite Anthracite 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 Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. An adze or adz (ædz is a tool used for smoothing rough-cut Wood in hand Woodworking. The Neolithic (from Greek νεολιθικός — neolithikos from νέος neos, "new" + λίθος lithos In the VSG, it was used to produce bracelets as well.

Amphibolite is a common dimension stone used in construction, paving, facing of buildings, etcetera especially because of its attractive textures, dark colour, hardness and polishability and its ready availability.

References

Winter, John D. , 2001. An introduction to Igneous and Metamorphic Petrology, 695 pages, Prentice Hall, ISBN 0-13-240342-0

Metamorphic facies - edit
Prehnite-pumpellyite | Zeolite | Greenschist | Blueschist | Eclogite | Amphibolite | Granulite
Historic definition The name facies was first used for specific Sedimentary environments in Sedimentary rocks by Swiss geologist Amanz The prehnite-pumpellyite facies is a metamorphic facies typical of subseafloor alteration of the Oceanic crust around Mid-ocean ridge spreading centres Zeolite facies describes the mineral assemblage resulting from the pressure and temperature conditions of low-grade Metamorphism. Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered Mafic Volcanic rock Blueschist (ˈbluːʃɪst is a rock that forms by the Metamorphism of Basalt and rocks with similar composition at high Pressures and low Eclogite (ˈɛklədʒaɪt is a coarse-grained Mafic ( Basaltic in composition Metamorphic rock. Granulites are fine to medium–grained Metamorphic rocks that have experienced high Temperatures of metamorphism composed mainly of Feldspars sometimes associated

Dictionary

amphibolite

-noun

  1. (geology) Any of a class of metamorphic rock composed mainly of amphibole with some quartz etc.
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