Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered mafic volcanic rock. In Geology, petrology (from Greek πέτρα petra, rock and λόγος logos, knowledge is the study of rocks and the conditions on which Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change Mafic is an adjective describing a Silicate mineral or rock that is rich in magnesium and iron the term was derived by contracting "magnesium" and "ferric" Volcanic rock is an Igneous rock of volcanic origin Texture Volcanic rocks are usually fine-grained or Aphanitic to glassy in The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the rock. The chlorites are a group of phyllosilicate Minerals Chlorites can be described by the following four endmembers based on their chemistry via substitution For the community in Canada see Actinolite Ontario. For the Sailor Moon character Epidote is a Calcium Aluminium Iron sorosilicate Mineral, Ca2Al2(Fe3+Al(SiO4(Si2O7O(OH However, basalts may remain quite black if primary pyroxene does not revert to chlorite or actinolite. To qualify for the name a rock must also exhibit schistocity or some foliation or layering. An alternate term for these rocks is greenstone. The rock is derived from basalt, gabbro or similar rocks containing sodium-rich plagioclase feldspar, chlorite, epidote and quartz. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Gabbro (ˈɡæbrəʊ is a dark coarse-grained intrusive Igneous rock chemically equivalent to Basalt. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 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. This discusses some chlorine compounds Chlorite is also a type of mineral see Chlorite group. Epidote is a Calcium Aluminium Iron sorosilicate Mineral, Ca2Al2(Fe3+Al(SiO4(Si2O7O(OH Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Chlorite and epidote give the green colour [1].
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Petrology
Greenschist, as a rock type, is defined by the presence of the minerals chlorite + actinolite +/- albite +/- epidote. Greenschist often has a lepidoblastic, nematoblastic or schistose texure defined primarily by chlorite and actinolite. Greenschists often have some foliation resulting in mineral alignment, especially of chlorite and actinolite. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic Grain size is rarely coarse, due primarily to the mineral assemblage. Chlorite and to a lesser extent actinolite prefer small, flat or acicular crystal habits.
Greenschist Facies
Greenschist Facies is determined by the particular T-P conditions required to metamorphose basalt to form the typical greenschist facies minerals chlorite, actinolite, and albite. Greenschist facies results from low temperature, moderate pressure metamorphism. Metamorphic conditions which create typical greenschist facies assemblages are called the Barrovian Facies Sequence, and the lower-pressure Abukuma Facies Series. Temperatures of approximately 400 to 500 °C and depths of about 8 to 50 kilometers are the typical envelope of greenschist facies rocks. The equilibrium mineral assemblage of rocks subjected to Greenschist Facies conditions depends on primary rock composition.
- Basalt: chlorite + actinolite + albite +/- epidote
- Ultramafic: chlorite + serpentine +/- talc +/- tremolite +/- diopside +/- brucite
- Pelites: quartz +/- albite +/- k-feldspar +/- chlorite, muscovite, garnet, pyrophyllite +/- graphite
- Calc-silicates: calcite +/- dolomite +/- quartz +/- micas, scapolite, wollastonite, etc
In greater detail the greenschist facies is subdivided into subgreenschist, lower and upper greenschist. For the community in Canada see Actinolite Ontario. For the Sailor Moon character The serpentine group describes a group of common rock-forming hydrous Magnesium Iron phyllosilicate (()3 Minerals they Talc (derived from the Persian via Arabic talq) is a Mineral composed of Hydrated Magnesium Silicate with Tremolite is a member of the Amphibole group of Silicate minerals with composition Ca 2 Mg 5 Si 8 Diopside is a Monoclinic Pyroxene Mineral with composition MgCaSi2O6 Brucite is the Mineral form of Magnesium hydroxide, with the chemical formula Mg ( OH)2 Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Albite is a plagioclase Feldspar Mineral. It is the sodium endmember of the Plagioclase Solid solution series Muscovite (also known as Common Mica, Isinglass, or Potash mica) is a phyllosilicate Mineral of Aluminium The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives Pyrophyllite is a phyllosilicate Mineral species belonging to the Clay family and composed of Aluminium Silicate Hydroxide The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed Scapolite (Gr asairos, rod stone is a group of rock-forming Silicate minerals composed of Aluminium, Calcium and Sodium Silicate Lower temperatures are transitional with and overlap the prehnite-pumpellyite facies and higher temperatures overlap with and include sub-amphibolite facies. Prehnite is a phyllosilicate of Calcium and Aluminium with the formula Ca2Al(AlSi3O10(OH2 Pumpellyite is a sorosilicate mineral rather a group of closely related minerals or Solid solution series pumpellyite-(Mg Ca2MgAl2(SiO4(Si2O7(OH2·(H2O Amphibolite (æmˈfɪbəlaɪt is the name given to a rock consisting mainly of hornblende Amphibole, the use of the term being restricted however to Metamorphic
If burial continues along Barrovian Sequence metamorphic trajectories, greenschist facies gives rise to Amphibolite Facies assemblages, dominated by amphibole and eventually to granulite facies. Amphibolite (æmˈfɪbəlaɪt is the name given to a rock consisting mainly of hornblende Amphibole, the use of the term being restricted however to Metamorphic Granulites are fine to medium–grained Metamorphic rocks that have experienced high Temperatures of metamorphism composed mainly of Feldspars sometimes associated Lower pressure, normally contact metamorphism produces albite-epidote hornfels while higher pressures at great depth produces eclogite. 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 Albite is a plagioclase Feldspar Mineral. It is the sodium endmember of the Plagioclase Solid solution series Hornfels ( German, meaning "hornstone" is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat Eclogite (ˈɛklədʒaɪt is a coarse-grained Mafic ( Basaltic in composition Metamorphic rock.
Oceanic basalts in the vicinity of mid-ocean ridges typically exhibit sub-greenschist alteration. A mid-ocean ridge or mid-oceanic ridge is an underwater Mountain range typically having a valley known as a Rift running along its axis formed by The greenstone belts of the various archean cratons are commonly altered to the greenschist facies. Greenstone belts are zones of variably metamorphosed Mafic to Ultramafic Volcanic sequences with associated Sedimentary rocks that A craton ( Greek kratos / κρἀτος ( neut. "strength" is an old and stable part of the Continental crust that has survived These ancient rocks are noted as host rocks for a variety of ore deposits in Australia, Namibia and Canada. For a topic outline on this subject see List of basic Australia topics. Namibia, officially the Republic of Namibia, is a country in Southern Africa on the Atlantic coast Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page
Culture
Europe
Greenschist rocks have been used to make axes across Europe. Several sites including Langdale axe industry have been identified. The Langdale axe industry is the name given by archaeologists to the centre of a specialised Stone tool manufacturing at Great Langdale in England 's
Eastern North America
A form of chlorite schist was popular in prehistoric Native American communities for the production of axes and celts, as well as ornamental items. Celt tool Transyslvaniajpg|right|thumb|250px|Celts from Transylvania In the Middle Woodland period, greenschist was one of the many trade items that were part of the Hopewell culture exchange network, sometimes transported over thousands of kilometers. The Hopewell tradition (also incorrectly called the "Hopewell culture" is the term used to describe common aspects of the Native American culture that flourished along
During the time of the Mississippian culture, the polity of Moundville apparently had some control over the production and distribution of greenschist. The Mississippian culture was a mound-building Native American culture that flourished in what is now the Midwestern, Eastern, and Southeastern Moundville Archaeological Site, also known as the Moundville Archaeological Park, is a Mississippian site on the Black Warrior River in Hale County The Moundville source has been shown to be from two localities in the Hillabee Formation of central and eastern Alabama.
See also
- Greenstone belt
- Metamorphism
- List of rock types
- List of minerals
- Pounamu, another type of rock frequently called greenstone
References
- Blatt, Harvey and Robert J. Greenstone belts are zones of variably metamorphosed Mafic to Ultramafic Volcanic sequences with associated Sedimentary rocks that 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 This page is intended as a list of all rock types A Amphibolite Andesite Anorthosite Anthracite This is a List of Minerals for which there are Wikipedia articles Pounamu' is the Māori name for several hard durable and highly valued types of stone - the New Zealand English term is "greenstone" Tracy (1996). Petrology; Igneous, Sedimentary, and Metamorphic, 2nd Ed. , W. H. Freeman. ISBN 0-7167-2438-3.
- Gall, Daniel G. and Vincas P. Steponaitis, "Composition and Provenance of Greenstone Artifacts from Moundville," Southeastern Archaeology 20(2):99-117 [2001]).
- Steponaitis, Vincas P. Prehistoric Archaeology in the Southeastern United States, 1970-1985. Annual Review of Anthropology, Vol. 15. (1986), pp. 363-404.
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