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Gneiss, a foliated metamorphic rock. Quartzite, a non-foliated metamorphic rock. Foliation in geology refers to repetitive layering in metamorphic rocks. [1] Each layer can be as thin as a sheet of paper, or over a meter in thickness. [1] The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. [1]
Quartzite can have a grainy, glassy, sandpaper-like surface. Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. [1] [2] Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts.
Quartzite – Hard, non-foliated metamorphic rock – A metamorphosed sandstone typically composed of >95% quartz; Schist – Easily split medium-grained metamorphic rock; Serpentinite – Rock formed by transformation of olivine; Skarn – Hard, coarse-grained, hydrothermally altered metamorphic rocks
The main use of foliated atlases is to link their overlapping plaques to form the leaves of a foliation. For this and other purposes, the general definition of foliated atlas above is a bit clumsy. One problem is that a plaque of (U α,φ α) can meet multiple plaques of (U β,φ β). It can even happen that a plaque of one chart meets ...
The surrounding rock may be "baked" through contact metamorphism, resulting in non-foliated metamorphic rocks. [1] Rocks that were originally limestone, quartz sandstone, and shale become marble, quartzite, and hornfels, respectively. [citation needed]
An incohesive fault rock with more than 30% fragments is a fault breccia and cohesive fault rocks are either of the cataclasite series (non foliated) or the mylonite series (foliated). [2] This was later modified to include foliated cataclasite. [5] This classification scheme was further simplified for ease of the classification in the field.
Granoblastic is an adjective describing an anhedral phaneritic equi-granular metamorphic rock texture. Granoblastic texture is typical of quartzite, marble, charnockites and other non-foliated metamorphic rocks without porphyroblasts.
This results in a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them. Foliated rock often develops planes of cleavage. Slate is an example of a foliated metamorphic rock, originating from shale, and it typically shows well-developed cleavage that allows slate to be split into thin plates. [19]