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  2. Metamorphism - Wikipedia

    en.wikipedia.org/wiki/Metamorphism

    Slate in turn is converted to phyllite, which is fine-grained and found in areas of low grade metamorphism. Schist is medium to coarse-grained and found in areas of medium grade metamorphism. High-grade metamorphism transforms the rock to gneiss, which is coarse to very coarse-grained. [37]

  3. Metamorphic facies - Wikipedia

    en.wikipedia.org/wiki/Metamorphic_facies

    The albite-epidote-hornfels facies is a facies at low pressure and relatively low temperatures. It is named for the two minerals albite and epidote, though they are also stable in other facies. Hornfels is a rock formed by contact metamorphism, a process that characteristically involves high temperatures but low pressures/depths. This facies is ...

  4. Metamorphic rock - Wikipedia

    en.wikipedia.org/wiki/Metamorphic_rock

    The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over 500 °C (932 °F)) metamorphism to the amphibolite or granulite facies. These form most of the exposed rock in Archean cratons.

  5. Metamorphic zone - Wikipedia

    en.wikipedia.org/wiki/Metamorphic_zone

    In contact metamorphism (metamorphism caused by high temperatures at low pressure in the vicinity of an igneous intrusion) a local contact aureole of zones is formed around a heat source. In rocks in subduction zones , that are transported to great depths in relatively low temperatures, rare types of metamorphic zones can develop.

  6. Index mineral - Wikipedia

    en.wikipedia.org/wiki/Index_mineral

    Map of index minerals of the Barrovian metamorphic zones of Scotland. An index mineral is used in geology to determine the degree of metamorphism a rock has experienced. . Depending on the original composition of and the pressure and temperature experienced by the protolith (parent rock), chemical reactions between minerals in the solid state produce new mi

  7. Illite crystallinity - Wikipedia

    en.wikipedia.org/wiki/Illite_crystallinity

    This low grade metamorphic technique can also be put into use when there is an absence in change of mineral structure which applies to higher grade metamorphism. [2] Early use of illite crystallinity was in the petroleum industry to determine the transition from a dry gas phase to an unproductive rock.

  8. Cleavage (geology) - Wikipedia

    en.wikipedia.org/wiki/Cleavage_(geology)

    The foliations are symmetrically arranged with respect to the axial plane, depending on the composition and competency of a rock. 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 ...

  9. Subduction zone metamorphism - Wikipedia

    en.wikipedia.org/wiki/Subduction_zone_metamorphism

    The onset of a low-pressure phase of lawsonite is the most significant marker of prehnite-pumpellyite facies metamorphism. The occurrence of lawsonite is significant because lawsonite contains 11 wt.% H 2 O [18] which is released at higher grade and can initiate significant melting. [8] Laumontite = Lawsonite + Quartz + H 2 O [19]