foliatedkivilajit

Foliatedkivilajit, or foliated metamorphic rocks, are a group of rocks formed under directed pressure that causes minerals to realign and recrystallize in a preferred orientation. This foliation creates planar or linear features, which can be observed in hand specimens and thin sections. The texture reflects the stress history and temperature conditions experienced during metamorphism.

The principal foliated rock types are slate, phyllite, schist, and gneiss, which differ mainly in grain size and the appearance of foliation. Slate has very fine grains and breaks along smooth cleavage planes. Phyllite shows a glossy sheen due to fine mica flakes. Schist possesses medium to coarse grains with prominent mineral grains and schistosity, a well-developed planar fabric. Gneiss exhibits banded light and dark mineral layers resulting from partial melting or high-grade metamorphism. At the highest grades, migmatites form, displaying partial melting and a mixed igneous–metamorphic texture.

Mineralogy commonly includes platy or elongated minerals such as micas (muscovite, biotite), along with quartz, feldspars, and sometimes garnet or pyroxene. The alignment of these minerals under differential stress produces foliation and, in some rocks, lineation or mineral banding. Foliated rocks typically originate from sedimentary or igneous protoliths subjected to regional metamorphism in tectonic settings like mountain belts or shear zones.

Foliatedkivilajit are distinct from nonfoliated metamorphic rocks (such as marble, quartzite, and hornfels), which lack a systematic planar fabric because they form under relatively uniform pressure or high temperatures without directed stress.