Foliation Metamorphic rock

folded foliation in metamorphic rock near geirangerfjord, norway

the layering within metamorphic rocks called foliation (derived latin word folia, meaning leaves ), , occurs when rock being shortened along 1 axis during recrystallization. causes platy or elongated crystals of minerals, such mica , chlorite, become rotated such long axes perpendicular orientation of shortening. results in banded, or foliated rock, bands showing colors of minerals formed them.

textures separated foliated , non-foliated categories. foliated rock product of differential stress deforms rock in 1 plane, creating plane of cleavage. example, slate foliated metamorphic rock, originating shale. non-foliated rock not have planar patterns of strain.

rocks subjected uniform pressure sides, or lack minerals distinctive growth habits, not foliated. rock has been subject differential stress, type of foliation develops depends on metamorphic grade. instance, starting mudstone, following sequence develops increasing temperature: slate fine-grained, foliated metamorphic rock, characteristic of low grade metamorphism, while phyllite fine-grained , found in areas of low grade metamorphism, schist medium coarse-grained , found in areas of medium grade metamorphism, , gneiss coarse coarse-grained, found in areas of high-grade metamorphism. marble not foliated, allows use material sculpture , architecture.

another important mechanism of metamorphism of chemical reactions occur between minerals without them melting. in process atoms exchanged between minerals, , new minerals formed. many complex high-temperature reactions may take place, , each mineral assemblage produced provides clue temperatures , pressures @ time of metamorphism.

metasomatism drastic change in bulk chemical composition of rock occurs during processes of metamorphism. due introduction of chemicals other surrounding rocks. water may transport these chemicals rapidly on great distances. because of role played water, metamorphic rocks contain many elements absent original rock, , lack present. still, introduction of new chemicals not necessary recrystallization occur.