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Likewise, a metamorphic rock whose protolith is known to be a conglomerate will be described as a metaconglomerate. For a metamorphic rock to be classified in this manner, the protolith should be identifiable from the characteristics of the metamorphic rock itself, and not inferred from other information. [22] [23] [24]
Gneiss (/ n aɪ s / nice) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F).
[33] [34] Subsequent erosion of the mountains exposes the roots of the orogenic belt as extensive outcrops of metamorphic rock, [35] characteristic of mountain chains. [33] Metamorphic rock formed in these settings tends to shown well-developed foliation. [33] Foliation develops when a rock is being shortened along one axis during metamorphism.
The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
Rock outcrop along a mountain creek near Orosí, Costa Rica. Rocks are classified according to characteristics such as mineral and chemical composition, permeability, texture of the constituent particles, and particle size. These physical properties are the result of the processes that formed the rocks. [5]
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]
Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic rock. [1]
The platiness gives the rock schistosity (a tendency to split into layers). Other common minerals include quartz, orthoclase, talc, carbonate minerals and amphibole . [1] Greenschist is a general field petrologic term for metamorphic or altered mafic volcanic rock. In Europe, the term prasinite is sometimes used.