Download - 2 - Nomenclatura de RM[1]
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1Nomenclatura e classificao das
rochas metamrficas
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2Nomenclatura das rochas metamrficas
No h uma rgida classificao para a nomenclatura das rochas
metamrficas. Como resultado h muita flexibilidade e o nome pode
fornecer informaes sobre:
A natureza do material parental
Textura da rocha
Assemblia mineral
As rochas metamrficas so designadas, em geral, por um
termo base ao qual podem, e em certos casos devem, ser
agregados outros termos, antes e/ou aps o termo base.
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Foliao gnissica do tipo facoidal ou ocelar em gnaisse.
Cristais anedrais de quartzo e subhedrais de plagioclsio com baixa birrefringncia, em gnaisse. Como acessrios, ocorrem cristais lamelares esverdeados de clorita e euedrais acastanhados de titanita; nicis cruzados; aumento 40x.
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Nestes, ocorrem fases rochosas mais escuras representando, normalmente, os relictos (paleossoma) no fundidos da rocha original e fases mais flsicasrepresentando a parte fundida (neossoma). Em condies anidras, nas mesmas temperaturas e presses de migmatitos, com pouca ou nenhuma fuso dissociando a fase mfica de flsica, formam-se os granulito ao invs de migmatitos.
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Gondito com veios de quartzo, rocha escuradevido presena de mangans. Orientao em gondito, com cristais opacos de pirolusita e quartzo; nicis paralelos; aumento 32x.
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7Itabirito com domnios ricos em quartzo (parte clara) intercalado com niveis ricos em hematita configurando uma dobra.
Itabirito com bandas de quartzo (parte escura) e de minerais claros (hematita/martita); nicis paralelos; visualizao sob luz refletida; aumento 25x.
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Srie tpica de evoluo de graus mais baixos para mais de metamorfismo de rochaspelticas :
ardsia filito xisto ganisse migmatito ou granulito
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