Editing Feldspar (section)

==Weathering==
[[Weathering|Chemical weathering]] of feldspars happens by [[hydrolysis]] and produces [[clay mineral]]s, including [[illite]], [[smectite]], and [[kaolinite]]. Hydrolysis of feldspars begins with the feldspar dissolving in water, which happens best in acidic or basic solutions and less well in neutral ones.<ref name=":0">{{Citation|last=Blum|first=Alex E.|title=Feldspars in Weathering|date=1994|url=https://doi.org/10.1007/978-94-011-1106-5_15|work=Feldspars and their Reactions|pages=595–630|editor-last=Parsons|editor-first=Ian|series=NATO ASI Series|place=Dordrecht|publisher=Springer Netherlands|language=en|doi=10.1007/978-94-011-1106-5_15|isbn=978-94-011-1106-5|access-date=2020-11-18}}</ref> The speed at which feldspars are weathered is controlled by how quickly they are dissolved.<ref name=":0" /> Dissolved feldspar reacts with H<sup>+</sup> or OH<sup>−</sup> ions and precipitates clays. The reaction also produces new [[ion]]s in solution, with the variety of ions controlled by the type of feldspar reacting.

The abundance of feldspars in the Earth's [[Crust (geology)|crust]] means that clays are very abundant weathering products.<ref>{{Cite book|last1=Hefferan|first1=Kevin|title=Earth Materials|last2=O'Brien|first2=John|publisher=Wiley-Blackwell|year=2010|isbn=978-1-4443-3460-9|pages=336–337}}</ref> About 40% of [[mineral]]s in [[sedimentary rock]]s are clays and clays are the dominant minerals in the most common sedimentary rocks, [[mudrock]]s.<ref name=":1">{{cite web|last=Nelson|first=Stephen A.|date=Fall 2008|title=Weathering & Clay Minerals|url=http://www.tulane.edu/~sanelson/eens211/weathering&clayminerals.htm|access-date=2008-11-13|work=Professor's lecture notes (EENS 211, Mineralogy)|publisher=Tulane University}}</ref> They are also an important component of [[soil]]s.<ref name=":1" /> Feldspar that has been replaced by clay looks chalky compared to more crystalline and glassy unweathered feldspar grains.<ref>{{Cite book|last=Earle|first=Steven|url=https://opentextbc.ca/geology/chapter/5-2-chemical-weathering/|title=Physical Geology|chapter=5.2 Chemical Weathering|date=September 2015|publisher=BCcampus}}</ref>

Feldspars, especially plagioclase feldspars, are not very stable at the Earth's surface due to their high formation temperature.<ref name=":1" /> This lack of stability is why feldspars are easily weathered to clays. Because of this tendency to weather easily, feldspars are usually not prevalent in sedimentary rocks. Sedimentary rocks that contain large amounts of feldspar indicate that the sediment did not undergo much chemical weathering before being buried. This means it was probably [[Sediment transport|transported]] a short distance in cold and/or dry conditions that did not promote weathering, and that it was quickly buried by other sediment.<ref name=":2">{{Cite web|title=Arkose|url=https://www.mindat.org/min-49127.html|access-date=2020-11-18|website=www.mindat.org}}</ref> Sandstones with large amounts of feldspar are called [[arkose]]s.<ref name=":2" />