Zeolite facies
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'''Zeolite facies''' describes the mineral assemblage resulting from the pressure and temperature conditions of low-grade [[metamorphism]].
<!-- Unsourced image removed: [[Image:Metamorphic Facies.JPG||right|thumb|300px|Zeolitic facies form at the lowest temperature and pressure]] -->
The zeolite facies is generally considered to be transitional between [[Diagenesis|diagenetic]] processes which turn sediments into [[sedimentary rock]]s, and [[prehnite-pumpellyite facies]], which is a hallmark of subseafloor alteration of the [[oceanic crust]] around [[mid-ocean ridge]] spreading centres. The zeolite and prehnite-pumpellyite facies are considered ''burial metamorphism'' as the processes of [[orogeny|orogenic]] regional metamorphism are not required.
Zeolite facies is most often experienced by pelitic sediments; rocks rich in aluminium, silica, potassium and sodium, but generally low in iron, magnesium and calcium. Zeolite facies metamorphism usually results in the production of low temperature [[clay]] minerals into higher temperature polymorphs such as [[kaolinite]] and [[vermiculite]].
Mineral assemblages include kaolinite and [[montmorillonite]] with [[laumontite]], [[wairakite]], [[prehnite]], [[calcite]] and [[chlorite]]. [[Phengite]] and [[adularia]] occur in potassium rich rocks. Minerals in this series include [[zeolite]]s, [[albite]], and [[quartz]].
This occurs by dehydration of the clays during compaction, and heating due to blanketing of the sediments by continued deposition of sediments atop it. Zeolote facies is considered to start with temperatures of approximately 50 - 150 °C and some burial is required, usually 1 - 5 km.
Zeolite facies tends to correlate in clay-rich sediments with the onset of a bedding plane [[Foliation (geology)|foliation]], parallel with the bedding of the rocks, caused by alignment of platy clay minerals in a horizontal orientation which reduces their free energy state.
Generally [[plutonic]] and [[volcanic]] rocks are not affected overly much by zeolite facies metamorphism, although [[vesicular]] [[basalt]]s and the like will have their vesicles flled with [[zeolite]] minerals, forming [[amygdule|amygdaloidal]] texture.
==See also==
* [[Diagenesis]]
* [[List of rock textures]] or [[rock microstructure]]
==References==
* Blatt, Harvey and Robert Tracy, 1995, ''Petrology: igneous, sedimentary, and metamorphic,'' Freeman, ISBN 0-7167-2438-3
{{Metamorphic Facies}}
[[Category:Metamorphic rocks]]
[[it:Facies zeolitica]]