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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.
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]
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.
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]
For example, when mixed sandstone and mudstone sequences are folded during very-low to low grade metamorphism, cleavage forms parallel to the fold axial plane, particularly in the clay-rich parts of the sequence. In folded alternations of sandstone and mudstone the cleavage has a fan-like arrangement, divergent in the mudstone layers and ...
For example, roof slate referred to shale above a coal seam, and draw slate referred to shale that fell from the mine roof as the coal was removed. [ 16 ] The British Geological Survey recommends that the term "slate" be used in scientific writings only when very little else is known about the rock that would allow a more definite classification.
Foliated metaconglomerate is created under the same metamorphic conditions that produce slate or phyllite, but with the parent rock being conglomerate, rather than clay. [2] The metaconglomerates of the Jack Hills of Western Australia are the source rocks for much of the detrital zircons that have been dated to be as old as 4.4 billion years.