mullite
{{Short description|Nesosilicate mineral}}
{{Infobox mineral
| name = Mullite
| category = Nesosilicate
| image = Osumilite, thick tabulars with Mullite - Ochtendung, Eifel, Germany.jpg
| imagesize = 260px
| caption = White, filamentous mullite in front of thicker osumilite platelets
(Photo width 1.5 mm)
Found in Wannenköpfe, Ochtendung, Eifel, Germany
| formula = Al6Si2O13
| molweight =
| strunz = 9.AF.20
| system = Orthorhombic
| class = Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
| symmetry = Pbnm, Pnnm
| unit cell = a = 7.5785(6) Å,
b = 7.6817(7) Å,
c = 2.8864(3) Å; Z = 1
| color = Colorless to pale pink or grey
| habit = Prismatic to acicular crystals
| twinning =
| cleavage = Good on [010]
| fracture =
| opticalprop = Biaxial (+)
| refractive = nα = 1.642 - 1.653 nβ = 1.644 - 1.655 nγ = 1.654 - 1.679
| birefringence = δ = 0.012 - 0.026
| pleochroism =
| 2V = Measured: 20° to 50°
| dispersion =
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| references = [https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Mullite Mineralienatlas]http://rruff.geo.arizona.edu/doclib/hom/mullite.pdf Handbook of Mineralogyhttp://www.mindat.org/min-2806.html Mindathttp://webmineral.com/data/Mullite.shtml Webmineral
}}
Mullite or porcelainite{{cite book | title=Glossary of Geology |edition=5th | publisher=American Geological Institute |editor-last=Neuendorf |editor-first=K.K.E. |editor-last2=Mehl |editor-first2=J.P. Jr. |editor-last3=Jackson |editor-first3=J.A.| year=2005 | location=Alexandria, Virginia | page=428 | isbn=978-0922152896}} is a rare silicate mineral formed during contact metamorphism of clay minerals. It can form two stoichiometric forms: 3Al2O32SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, there are three different aluminium sites: two distorted tetrahedral and one octahedral.
Mullite was first described in 1924 for an occurrence on the Isle of Mull, Scotland. It occurs as argillaceous inclusions in volcanic rocks in the Isle of Mull, inclusions in sillimanite within a tonalite at Val Sissone, Italy and with emerylike rocks in Argyllshire, Scotland.
Porcellanite
Mullite (porcelainite) can be found as a constituent mineral in a type of thermally-metamorphosed rock called porcellanite.{{cite journal | url=http://geolines.gli.cas.cz/fileadmin/volumes/volume15/G15-035.pdf | title=North Bohemian Porcellanites and their Mineral Composition: the Case of the Dobrčice Quarry, the Most Basin | first1=F. | last1=Fediuk | first2=A. | last2=Langrova | first3=K. | last3=Melka | journal=Geolines | year=2003 | volume=15 | pages=35–43}}
Use in porcelain
Mullite is present in the form of needles in porcelain.{{cite book
|editor=Kingery, W.D.
|title=Ceramic Fabrication Processes
|publisher=John Wiley & Sons, Inc.
|location=New York City
|year=1960}}
It is produced during various melting and firing processes, and is used as a refractory material,H. Schneider & S. Komarneni (2005) Mullite. Wiley, VCH, 509 pp, {{ISBN|3-527-30974-8}} because of its high melting point of 1840 °C.{{cite web
|author=Kyanite Mining Corporation
|title=Virginia Mullite
|date=2009-10-25
|url=http://www.kyanite.com/mullite.html
}}
In 2006 researchers at University College London and Cardiff University discovered that potters in the Hesse region of Germany since the late Middle Ages had used mullite in the manufacture of a type of crucible (known as Hessian crucibles), that were renowned for enabling alchemists to heat their crucibles to very high temperatures.{{cite web
|author=University College London
|authorlink=University College London
|date=2006-11-23
|title=21st Century Technology Cracks Alchemists' Secret Recipe
|url=https://www.sciencedaily.com/releases/2006/11/061123120134.htm
|work=Science Daily
|publisher=ScienceDaily LLC
|accessdate=2008-01-12}}{{cite journal
|author=Martinon-Torres M.
|year=2005
|title=Mass-produced mullite crucibles in medieval Europe: Manufacture and material properties
|author2=Freestone I.C.
|author3=Hunt, A.
|author4=Rehren, T.
|journal=Journal of the American Ceramic Society
|volume=91
|issue=6
|pages=2071–2074
|doi=10.1111/j.1551-2916.2008.02383.x
}} The formula finally replicated in the above studies (using kaolinitic clay and then firing it at temperatures above 1100 °C) was kept a closely guarded secret by those crucible makers since the 15th century.
Mullite morphology is also important for its application. In this case, there are two common morphologies for mullite. One is a platelet shape with low aspect ratio and the second is a needle shape with high aspect ratio. If the needle shape mullite can form in a ceramic body during sintering, it has an effect on both the mechanical and physical properties by increasing the mechanical strength and thermal shock resistance. The most important condition relates to ceramic chemical composition. If the silica and alumina ratio with low basic materials such as sodium and calcium is adjusted, the needle shape mullite forms at about 1400 °C and the needles will interlock. This mechanical interlocking contributes to the high mechanical strength of porcelain.{{cite web |url= https://digitalfire.com/material/mullite |title= Mullite |first1= Tony |last1= Hanson |publisher= digitalfire.com |access-date= 2023-05-21}}{{cite web |url= https://www.ceramic-research.com/articles_01.html |title= Vitrification Behaviour of The Porcelain Tile |publisher= Ceramics Research Co. |date= 2012 |access-date= May 21, 2023}}
Use as a catalyst
Further recent research indicates that a synthetic analogue of mullite can be an effective replacement for platinum in diesel engines for exhaust management.{{cite journal|last=Wang|first=W. |author2=G. McCool |author3=N. Kapur |author4=G. Yuan |author5=B. Shan |author6=M. Nguyen |author7=U. M. Graham |author8=B. H. Davis |author9=G. Jacobs |author10=K. Cho |author11=X. Hao|title=Mixed-Phase Oxide Catalyst Based on Mn-Mullite (Sm, Gd)Mn2O5 for NO Oxidation in Diesel Exhaust|journal=Science|date=17 August 2012|volume=337|issue=6096|pages=832–835|doi=10.1126/science.1225091|url=https://www.science.org/doi/full/10.1126/science.1225091|accessdate=2012-08-16|bibcode = 2012Sci...337..832W |pmid=22904009|s2cid=27948924 |url-access=subscription}}
Notes
{{reflist}}
- {{cite journal |author=Martinón-Torres, Marcos |author2=Thilo Rehren |author3=Ian C. Freestone |date=November 2006 |title=Mullite and the mystery of Hessian wares |url=http://www.ucl.ac.uk/archaeology/staff/profiles/martinon/Martinon-Torres%20et%20al%202006%20Nature.pdf |format=PDF online reproduction|journal=Nature |volume=444 |issue=7718 |pages=437–438 |publisher=Nature Publishing Group |location=London |doi=10.1038/444437a |pmid=17122847|bibcode = 2006Natur.444..437M |s2cid=4362496 }}
- {{cite book |author=Schneider, Hartmut |year=2005 |chapter=General Introduction |title=Mullite |editor=Hartmut Schneider |editor2=Sridhar Komarneri|location=Weinheim, Germany |publisher=Wiley-VCH |pages=xv–xx |isbn=978-3-527-30974-0 |oclc=58051400}}
- {{cite web|title=Sithean Sluaigh, Strathclyde, Scotland, UK|url=http://www.mindat.org/loc-5100.html|website=MinDat|publisher=MinDat|accessdate=6 November 2015}}
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Category:Orthorhombic minerals