Peralkaline rocks include those igneous rocks which have a deficiency of aluminium such that sodium and potassium are in excess of that needed for feldspar. The presence of aegerine (sodium pyroxene) and riebeckite (sodium amphibole) are indicative of peralkaline conditions. Examples are the peralkaline rhyolites, comendite and pantellerite, with comendite being the more felsic (silica-rich) rock. Another example is the peralkaline granite that forms the islet of Rockall in the North Atlantic Ocean.
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| - Peralkalien (nl)
- Peralkaline rock (en)
- Rocha peralcalina (pt)
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| - Rocha peralcalina é a designação dada em geoquímica e petrologia às rochas ígneas que apresentam na sua composição uma baixa concentração de alumínio (Al) de tal forma que o somatório das concentrações de sódio (Na) e potássio (K) estejam em excesso em relação ao necessário para permitir a formação de feldspatos. A presença de aegerina (piroxena sódica) e riebeckita (anfíbola sódica) são indicadores da existência de peralcalinidade. A presença de rochas peralcalinas é considerada um sinal seguro da existência de vulcanicidade associada a uma bacia de rifte continental. (pt)
- Peralkaline rocks include those igneous rocks which have a deficiency of aluminium such that sodium and potassium are in excess of that needed for feldspar. The presence of aegerine (sodium pyroxene) and riebeckite (sodium amphibole) are indicative of peralkaline conditions. Examples are the peralkaline rhyolites, comendite and pantellerite, with comendite being the more felsic (silica-rich) rock. Another example is the peralkaline granite that forms the islet of Rockall in the North Atlantic Ocean. (en)
- Peralkalien (Engels: peralkaline) staat in de petrologie en vulkanologie voor stollingsgesteente, magma of lava dat minder oxide van aluminium bevat dan oxiden van kalium en natrium samen. Peralkalien gesteente is "onderverzadigd in aluminium" (Engels: alumina-undersaturated). Per definitie geldt dat de kleiner is dan 1: Al2O3 / [Na2O + K2O] < 1 Peralkalien gesteente wordt soms onderverdeeld in , dat relatief minder arm is in aluminium, en , dat relatief arm is in aluminium. (nl)
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| - Peralkaline rocks include those igneous rocks which have a deficiency of aluminium such that sodium and potassium are in excess of that needed for feldspar. The presence of aegerine (sodium pyroxene) and riebeckite (sodium amphibole) are indicative of peralkaline conditions. Examples are the peralkaline rhyolites, comendite and pantellerite, with comendite being the more felsic (silica-rich) rock. Another example is the peralkaline granite that forms the islet of Rockall in the North Atlantic Ocean. Peralkaline rocks are indicative of continental rift-related volcanicity (e.g. the peralkaline rhyolites of the East African Rift in central Kenya) as well as continental and oceanic hotspot volcanicity (e.g. the peralkaline rhyolites of the Glass House Mountains in eastern Australia and the Canary Islands in the Atlantic Ocean). Peralkaline rocks related to subduction zone volcanicity have also been reported (e.g. Sardinia in Italy). Peralkaline magmas likely form when fractional crystallization removes a high proportion of plagioclase relative to mafic minerals. (en)
- Peralkalien (Engels: peralkaline) staat in de petrologie en vulkanologie voor stollingsgesteente, magma of lava dat minder oxide van aluminium bevat dan oxiden van kalium en natrium samen. Peralkalien gesteente is "onderverzadigd in aluminium" (Engels: alumina-undersaturated). Per definitie geldt dat de kleiner is dan 1: Al2O3 / [Na2O + K2O] < 1 Het gaat daarbij om molaire hoeveelheden. Gesteenten waarvan dit ratio groter is dan 1, maar waarvan de ratio van aluminiumoxide ten opzichte van natrium-, kalium- en calciumoxide samen wel kleiner is dan 1, worden metalumineus genoemd. Gesteenten waarin er verhoudingsgewijs meer aluminiumoxide is dan natrium-, kalium- en calciumoxide samen, worden peralumineus genoemd. Peralkalien gesteente wordt soms onderverdeeld in , dat relatief minder arm is in aluminium, en , dat relatief arm is in aluminium. De geringe hoeveelheid aluminium in peralkalien gesteente uit zich in de mineralogie. Zo komen in peralkalien gesteente Al-arme eindleden van mafische mineralen voor, zoals aegirien (een Al-loos van pyroxeen), riebeckiet, richteriet en aenigmatiet (alle drie Al-loze eindleden van amfibool). Omdat er ook weinig calcium in peralkalien gesteente zit, zal plagioklaas vooral uit albiet (natrium-plagioklaas) bestaan. (nl)
- Rocha peralcalina é a designação dada em geoquímica e petrologia às rochas ígneas que apresentam na sua composição uma baixa concentração de alumínio (Al) de tal forma que o somatório das concentrações de sódio (Na) e potássio (K) estejam em excesso em relação ao necessário para permitir a formação de feldspatos. A presença de aegerina (piroxena sódica) e riebeckita (anfíbola sódica) são indicadores da existência de peralcalinidade. A presença de rochas peralcalinas é considerada um sinal seguro da existência de vulcanicidade associada a uma bacia de rifte continental. (pt)
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