The Minerals of Metamorphosed Mafic Rocks Mafic rocks generally have igneous protoliths basalt and its coarsegrained equivalent gabbro Minerals of Metamorphosed Mafic Rocks Plagioclase Ca Na Al Si 4O8 like in igneous rocks Amphiboles double chain silicates Tremolite Actinolite Ca2 Mg Fe 5Si8O22 OH 2 light to dark green colorless in thin section Hornblende complex formula related to trem actin dark green to black green or brown in thin section Glaucophane blue sodic amphibole Actinolite Hornblende in thin section Glaucophane blue amphibole More Minerals of Metamorphosed Mafic Rocks Pyroxenes similar to those in igneous rocks Clinopyroxene diopside Ca Mg Fe Si2O6 light to dark green inclined extinction in microscope Orthopyroxene enstatite Mg Fe 2Si2O6 or Mg Fe SiO3 tan to brown parallel extinction in microscope More Minerals of Metamorphosed Mafic Rocks Epidote paired tetrahedra and isolated tetrahedra in a silicate view epidote movie Ca2 Al Fe3 Al2O SiO4 Si2O7 OH pistachio green like canned peas color is characteristic Chlorite dark green sheet silicate Mg Fe Al 6 Si Al 4O10 OH 8 Garnet red similar to that in meta pelitic rocks View Epidote Structure Movie Metamorphic Facies Different combinations of these minerals occur at different metamorphic conditions In 1920 Pentii Eskola a geology professor at the University of Helsinki Finland introduced the idea of Metamorphic Facies Metamorphic Facies group minerals of rocks that experienced similar ranges of pressure and temperature during metamorphism Metamorphic Facies are named for minerals in metamorphosed mafic rocks or meta basalts Metamorphic Facies in P and T Minerals in Meta basalt Greenschist albite actinolite epidote chlorite Epidote Amphibolite albite hornblende epidote Amphibolite plagioclase hornblende garnet Metamorphic Facies in P and T Minerals in Meta basalt Granulite clinopyroxene orthopyroxene plagioclase Blueschist albite blue amphibole lawsonite paired sil Eclogite bright green Na rich pyroxene garnet More next semester
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