Foliáció

Foliáció refers to the development of planar fabric in metamorphic rocks, distinguishing them from non-foliated rocks which lack any such orientation. This planar fabric is a result of the preferred orientation of platy or elongated minerals within the rock during metamorphism. The process is driven by directed pressure, or stress, which causes minerals to rotate and recrystallize into alignment.

The type of foliation depends on the intensity of metamorphism and the mineralogy of the original rock. Common types include slaty cleavage, where rocks split into thin, flat sheets; phyllitic texture, which exhibits a sheen due to fine mica growth; schistosity, characterized by visible, aligned micas and other minerals; and gneissic banding, a coarse-grained fabric with alternating light and dark mineral layers.

Foliation is a key indicator of the metamorphic conditions a rock has experienced, providing insights into the temperature, pressure, and stress history of the Earth's crust. Geologists use the orientation and type of foliation to reconstruct the tectonic forces and deformation events that shaped the rock. Understanding foliation is crucial in fields such as structural geology, petrology, and resource exploration.