Editing Andalusite

{{Short description|Aluminium nesosilicate mineral}}
{{Infobox mineral
| name        = Andalusite
| category    = [[Nesosilicates]] 
| image       = Andalusite - Malacheta, Minas Gerais, Brazil.jpg
| imagesize   = 260px
| alt         = 
| caption     = Andalusite
| formula     = Al<sub>2</sub>SiO<sub>5</sub>
| molweight   = 
|IMAsymbol=And| strunz      = 9.AF.10
| system      = [[Orthorhombic]]
| class       = Dipyramidal (mmm) <br/>[[H-M symbol]]: (2/m 2/m 2/m)
| symmetry    = ''Pnnm''
| unit cell   = a = 7.7980&nbsp;[[Ångstrom|Å]], b = 7.9031&nbsp;Å <br/>c = 5.5566&nbsp;Å; Z&nbsp;=&nbsp;4
| color       = Pink, violet, yellow, green, white, gray; in thin section, colorless to pink or green
| habit       = As euhedral crystals or columnar aggregates having nearly square cross sections; fibrous compact to massive
| twinning    = On {101}, rare
| cleavage    = Good on {110}, poor on {100}
| fracture    = uneven to subconchoidal
| mohs        = 6.5–7.5
| luster      = Vitreous
| polish      = 
| refractive  = n<sub>α</sub> = 1.629 – 1.640 n<sub>β</sub> = 1.633 – 1.644 n<sub>γ</sub> = 1.638 – 1.650
| opticalprop = double refractive, biaxial negative; ''chiastolite'' has anomalous aggregate reaction.<ref name=GIA/> 
| birefringence = δ = 0.009 – 0.010
| dispersion  = r < v strong
| pleochroism = strongly trichroic
| 2V          = 71–86°
| fluorescence= non-fluorescent 
| absorption  =
| streak      = White
| gravity     = 3.17 (± .04)
| density     = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = Transparent to nearly opaque with inclusions
| references  = <ref name=GIA>[[Gemological Institute of America]], ''GIA Gem Reference Guide'' 1995, {{ISBN|0-87311-019-6}}</ref><ref name=Handbook>http://rruff.geo.arizona.edu/doclib/hom/andalusite.pdf Handbook of Mineralogy</ref>
}}
'''Andalusite''' is an [[aluminium]] [[Silicate mineral|nesosilicate]] [[mineral]] with the chemical formula Al<sub>2</sub>SiO<sub>5</sub>. This mineral was called andalousite by Delamétherie,<ref>{{Cite journal|last=Delamétherie|first=Jean Claude|date=1798|title=Sur une pierre de l'Andalousie|journal=Journal de Physique, de Chimie d'Histoire Naturelle et des Arts|volume=46|pages=386–387}}</ref> who thought it came from [[Andalusia]], Spain. It soon became clear that it was a locality error, and that the specimens studied were actually from El Cardoso de la Sierra, in the Spanish province of [[Province of Guadalajara|Guadalajara]], not Andalusia.<ref>{{Cite book|title=Minerales y Minas de España. Vol. IX. Silicatos|last=Calvo|first=Miguel|publisher=Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo|year=2018|isbn=978-84-8321-883-9|location=Madrid, Spain|pages=91–94}}</ref>

Andalusite is trimorphic with [[kyanite]] and [[sillimanite]], being the lower pressure mid temperature polymorph. At higher temperatures and pressures, andalusite may convert to sillimanite. Thus, as with its other polymorphs, andalusite is an [[aluminosilicate]] index mineral, providing clues to depth and pressures involved in producing the host rock.<ref>{{Cite journal|last=Whitney, D.L.|date=2002|title=Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey|journal=American Mineralogist|volume=87|issue=4|pages=405–416|doi=10.2138/am-2002-0404|bibcode=2002AmMin..87..405W|s2cid=131616262}}</ref>
{{al2sio5 phase diagram}}
[[File:Round faceted andalusite 1.jpg|thumb|Round faceted andalusite]]

==Varieties==<!-- Viridite and Kanonaite redirect here-->
The variety [[chiastolite]] commonly contains dark inclusions of carbon or clay which form a [[cruciform]] pattern when shown in cross-section. This stone was known at least from the sixteenth century, being taken to many European countries, as a souvenir, by pilgrims returning from Santiago de Compostela.<ref>{{Cite journal|last=Calvo|first=Miguel|date=2016|title=El "lapis crucifer", "piedra de cruz de Compostela": un elemento importante de los patrimonios geológico y cultural del NW de España|journal=De Re Metallica|volume=6|pages=67–79}}</ref>

'''Viridine''' is a [[green]] variety of andalusite in which [[manganese]] 3+ substitutes for aluminium, the same change is also responsible for the colour.<ref>{{cite journal |last1=Abs-Wurmbach |first1=I. |last2=Langer |first2=K. |last3=Seifert |first3=F. |last4=Tillmanns |first4=Ε. |title=The crystal chemistry of (Mn 3+ , Fe 3+ )-substituted andalusites (viridines and kanonaite), (Al 1-x-y Mn x 3+ Fe 3+ y ) 2 (O{{!}}SiO 4 ): crystal structure refinements, Mössbauer, and polarized optical absorption spectra |journal=Zeitschrift für Kristallographie - Crystalline Materials |date=1 October 1981 |volume=155 |issue=1–4 |pages=81–114 |doi=10.1524/zkri.1981.155.14.81|s2cid=201671728 }}</ref><ref>{{Cite web |title=Minerals Colored by Metal Ions |url=http://minerals.gps.caltech.edu/color_causes/Metal_Ion/index.html |access-date=2023-03-01 |website=minerals.gps.caltech.edu}}</ref> '''Kanonaite''' is a greenish-black mineral related to andalusite and having the approximate composition {{chem2|(Mn0.76Al0.23Fe0.02)AlSiO5}}.<ref>{{cite journal |last1=Vrána |first1=S. |last2=Rieder |first2=M. |last3=Podlaha |first3=J. |title=Kanonaite, (Mn 0.76 3+ Al0.23Fe 0.02 3+ )[6]Al[5][O{{!}}SiO4], a new mineral isotypic with andalusite |journal=Contributions to Mineralogy and Petrology |date=1978 |volume=66 |issue=3 |pages=325–332 |doi=10.1007/BF00373417|s2cid=95925117 }}</ref>

A clear variety found in Brazil and Sri-Lanka can be cut into a gemstone.<ref>{{Cite web |url=http://www.gemstone.org/gem-by-gem/english/andalusite.html |title=''International Colored Gem Association: Anadalusite'' |access-date=2006-07-13 |archive-url=https://web.archive.org/web/20060717224731/http://www.gemstone.org/gem-by-gem/english/andalusite.html |archive-date=2006-07-17 |url-status = dead}}</ref> Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of [[iridescence]], although the colors are actually the result of unusually strong [[pleochroism]].<ref name="FernandesChoudhary2009">{{cite journal |last1=Fernandes |first1=Shyamala |last2=Choudhary |first2=Gagan |title=Gem-quality andalusite from Brazil |journal=Gems & Gemology |date=Summer 2009 |volume=45 |issue=2 |pages=120–129 |doi=10.5741/GEMS.45.2.120 |url=https://www.gia.edu/doc/Summer-2009-Gems-Gemology-Gem-Quality-Andalusite-from-Brazil.pdf |access-date=30 October 2021}}</ref>

== Occurrence ==
Andalusite is a common [[metamorphism|metamorphic]] mineral which forms under low pressure and low to high temperatures. The minerals [[kyanite]] and [[sillimanite]] are [[polymorphism (materials science)|polymorphs]] of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found. It is particularly associated with [[pelitic]] metamorphic rocks such as [[mica schist]].<ref name=Nesse2000>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=314–318}}</ref>

The world's highest concentration of andalusite is found in the [[Glomel andalusite mine|Glomel mine]] in [[Côtes-d'Armor]] ([[France]]) which accounts for 25% of the global production of this mineral.<ref>{{Cite web |date=2022-09-16 |title=Glomel : la mine d'andalousite ouvre ses portes au public ce samedi |url=https://www.letelegramme.fr/cotes-d-armor/rostrenen-22110/glomel-la-mine-d-andalousite-ouvre-ses-portes-au-public-ce-samedi-327738.php |access-date=2024-11-21 |website=Le Télégramme |language=fr-FR}}</ref> [[South Africa]] possesses the largest portion of the world's known andalusite deposits.<ref>{{cite journal |last1=Overbeek |first1=P. W. |date=1 June 1989 |title=Andalusite in South Africa |url=https://journals.co.za/doi/abs/10.10520/AJA0038223X_1910 |journal=Journal of the Southern African Institute of Mining and Metallurgy |volume=89 |issue=6 |pages=157–171 |access-date=25 October 2021 |hdl=10520/AJA0038223X_1910}}</ref>

== Uses ==
Andalusite is used as a [[refractory]] in furnaces, kilns and other industrial processes.<ref>{{cite journal |last1=Dubreuil |first1=P. |last2=Sobolev |first2=V. M. |last3=Filari |first3=E. |title=Use Of Andalusite Refractories In Ferrous Metallurgy |journal=Refractories and Industrial Ceramics |date=1999 |volume=40 |issue=5–6 |pages=252–259 |doi=10.1007/BF02762295 |s2cid=136482381 |url=https://link.springer.com/article/10.1007/BF02762295 |access-date=25 October 2021|url-access=subscription }}</ref> 

== See also ==
* [[List of minerals]]

== References ==
{{Commons category|Andalusite}}
{{Reflist}}

{{Authority control}}

[[Category:Aluminium minerals]]
[[Category:Nesosilicates]]
[[Category:Orthorhombic minerals]]
[[Category:Minerals in space group 58]]
[[Category:Industrial minerals]]
[[Category:Gemstones]]