1Nomenclatura e classificao das

rochas metamrficas

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.

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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