Editing Microcline

{{Short description|Igneous rock-forming tectosilicate mineral}}
{{Infobox mineral
| name        = Microcline
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| image       = Microcline-199473.jpg
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| caption     = 
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| SMILES           =
| Jmol             =
| category    = [[Tectosilicate]] [[minerals]], [[feldspar]] [[Mineral group|group]], [[Alkali feldspar|alkali]] series
| formula     = KAlSi<sub>3</sub>O<sub>8</sub>
| IMAsymbol   = Mcc<ref>{{Cite journal|author=L.N. Warr|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   = 
| strunz      = 
| dana        = 
| system      = [[Triclinic]]
| class       = 
| symmetry    = P{{overline|1}}  (no. 2)
| unit cell   = 
| color       = White, grey, greyish yellow, yellowish, tan, salmon-pink, bluish green, green.
| colour      = 
| habit       = Can be anhedral or euhedral. Grains are commonly elongate with a tabular appearance. May contain lamellae which formed from exsolved albite.
| twinning    = Typically displays [[albite twinning]] and [[pericline twinning]]. This combination leads to a grid pattern, hence microcline displays [[gridiron twinning]]. Can also display [[carlsbad twinning]], simple twins, or lack twinning altogether. Lamellae in microcline are discontinuous and "pinch and swell".
[[Image:Microcline.jpg|thumb|200px|[[Photomicrograph]] of [[thin section]] of microcline showing crosshatched [[crystal twinning]] (in cross [[Polarization (waves)|polarized]] light)]]
| cleavage    = Has perfect cleavage parallel to {001} and good cleavage on {010}. Cleavages intersect at 90°41'. It can be difficult to see cleavage in thin section due to microcline's low relief.
| fracture    = Uneven 
| tenacity    = Brittle
| toughness   = 
| mohs        = 6–6.5
| luster      = Vitreous
| streak      = White
| diaphaneity = Transparent, translucent
| gravity     = 2.5–2.6
| density     = 
| polish      = 
| opticalprop = Biaxial negative
| refractive  = nα = 1.514 – 1.529 nβ = 1.518 – 1.533 nγ = 1.521 – 1.539
| birefringence = Up to first order white (roughly 0.007)
| pleochroism =  N/A
| 2V          = 65–88°
| dispersion  = 
| extinction  = Inclined extinction to cleavage
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| fusibility  = 
| diagnostic  = Gridiron twinning distinguishes microcline from other feldspars. Distinguishable from plagioclase because the lamellae in plagioclase are continuous and do not "pinch and swell."
| solubility  = 
| impurities  = 
| alteration  = Commonly alters to sericite or clay.
| other       = 
| prop1       = Relief
| prop1text   = Low negative relief
| references  = 
| var1        = 
| var1text    = 
| var2        = Optical sign
| var2text    = Biaxial negative
| var3        = Color in [[Plane polarized light|PPL]]
| var3text    = Colorless
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}}
'''Microcline'''  (KAlSi<sub>3</sub>O<sub>8</sub>) is an important [[igneous rocks|igneous rock]]-forming [[tectosilicate]] [[mineral]]. It is a [[potassium]]-rich [[alkali feldspar]]. Microcline typically contains minor amounts of [[sodium]]. It is common in [[granite]] and [[pegmatite]]s. Microcline forms during slow cooling of [[orthoclase]]; it is more stable at lower temperatures than orthoclase. [[Sanidine]] is a [[Polymorphism (materials science)|polymorph]] of alkali feldspar stable at yet higher temperature. Microcline may be clear, white, pale-yellow, brick-red, or green; it is generally characterized by cross-hatch twinning that forms as a result of the transformation of [[monoclinic]] orthoclase into [[triclinic]] microcline.

The chemical compound name is potassium aluminium silicate, and it is known as [[E number]] reference '''E555'''.

==Geology==

Microcline may be chemically the same as [[monoclinic]] orthoclase, but because it belongs to the [[triclinic]] crystal system, the prism angle is slightly less than right angles; hence the name "microcline" from the [[Greek language|Greek]] "small slope". It is a fully ordered [[triclinic]] modification of [[potassium]] [[feldspar]] and is [[Polymorphism (materials science)|dimorphous]] with [[orthoclase]]. Microcline is identical to orthoclase in many physical properties, and can be distinguished by x-ray or optical examination. When viewed under a [[Petrographic microscope|polarizing microscope]], microcline exhibits a minute multiple [[Crystal twinning|twinning]] which forms a grating-like structure that is unmistakable.
[[Image:Amazonita1.jpeg|left|thumb|Feldspar (amazonite)]]
[[Perthite]] is either microcline or orthoclase with thin lamellae of exsolved albite.

Amazon stone, or [[amazonite]], is a green variety of microcline. It is not found anywhere in the [[Amazon Basin]], however. The [[Spain|Spanish]] explorers who named it apparently confused it with another green mineral from that region.

The largest documented single crystals of microcline were found in Devil's Hole Beryl Mine, [[Colorado]], US and measured ~50 × 36 × 14 m. This could be one of the largest crystals of any material found so far.<ref>{{cite journal| url = http://www.minsocam.org/ammin/AM66/AM66_885.pdf| journal = American Mineralogist| volume = 66| pages = 885–907| year= 1981| title= The largest crystals| author = P.C. Rickwood}}</ref>

Microcline is exceptionally active ice-nucleating agent in the atmosphere.<ref>{{cite journal| url = https://www.nature.com/articles/nature12278| journal = Nature| volume = 498| pages = 355–358| year= 2013| title= The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds| author = J.D. Atkinson, B.J. Murray, M.T. Woodhouse, T.F. Whale, K.J. Baustian, K.S. Carslaw, S. Dobbie, D. O'Sullivan, T.L. Malkin| issue = 7454| doi = 10.1038/nature12278| pmid = 23760484| bibcode = 2013Natur.498..355A}}</ref> Recently it has been possible to understand how water binds to the microcline surface.<ref>{{cite journal| journal = Journal of Physical Chemistry Letters| volume = 15| issue = 1| pages = 15–22| year= 2024| title= How Water Binds to Microcline Feldspar (001)| author = G. Franceschi, A. Conti, L. Lezuo, R. Abart, F. Mittendorfer, M. Schmid, U. Diebold| doi = 10.1021/acs.jpclett.3c03235| pmid = 38156776| pmc = 10788961}}</ref>

==As food additive==
The chemical compound name is potassium aluminium silicate, and it is known as [[E number]] reference '''E555'''. It was the subject in 2018 of a Call for technical and toxicological data from the [[EFSA]].<ref>{{cite web |title=Call for technical and toxicological data on sodium aluminium silicate (E 554) and potassium aluminium silicate (E 555) authorised as food additives in the EU |date=7 November 2018 |url=https://www.efsa.europa.eu/en/consultations/call/181107 |publisher=EFSA}}</ref>

In 2008, it (along with other Aluminum compounds) was the subject of 
a Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Food Contact Materials from the EFSA.<ref>{{cite journal |last1=F. Aguilar, H. Autrup, S. Barlow, L. Castle, R. Crebelli, W. Dekant, K.-H. Engel, N. Gontard, D. Gott, S. Grilli, R. Gürtler, J.-C. Larsen, C. Leclercq, J.-C. Leblanc, F.-X. Malcata, W. Mennes, M.-R. Milana, I. Pratt, I. Rietjens, P. Tobback, F. Toldrá. |title=Safety of aluminium from dietary intake[1] – Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Food Contact Materials (AFC) |journal=EFSA Journal |date=2008 |volume=6 |issue=7 |page=754 |doi=10.2903/j.efsa.2008.754 |url=https://www.efsa.europa.eu/en/efsajournal/pub/754|doi-access=free |pmid=37213837 |pmc=10193631 }}</ref>
==See also==
*[[List of minerals]]

==References==
{{reflist}}
*[http://www.utexas.edu/tmm/npl/mineralogy/science_of_minerals/alkalffeldsparseries.html Alkali feldspars U. Texas]
*[http://www.mindat.org/min-2704.html Mindat]

[[Category:Potassium minerals]]
[[Category:Aluminium minerals]]
[[Category:Tectosilicates]]
[[Category:Triclinic minerals]]
[[Category:Feldspar]]
[[Category:Luminescent minerals]]
[[Category:E-number additives]]
[[Category:Minerals in space group 2]]