Halloysite 2463425 219013433 2008-06-13T04:51:54Z DumZiBoT 6085301 robot Modifying: [[de:Halloysit-7Å]] [[Image:halloytemcx.jpg|right|thumb|200px|TEM Image of Halloysite Nanotubules (''unknown scale'')]] [[Image:Mineraly.sk - halloyzit.jpg|right|thumb|200px|A sample of Halloysite (''unknown scale'')]] [[Image:Halloysite variety Indianaite Hydrous Aluminum silicate Bedford, Lawrence County, Indiana 2770.jpg|thumb|right|200px|Halloysite from [[Indiana]]]] '''Halloysite''' is a 1:1 aluminosilicate [[clay]] [[mineral]] with the [[empirical formula]] Al<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>(OH)<sub>4</sub>. Its main constituents are [[aluminium]] (20.90%), [[silicon]] (21.76%), and [[hydrogen]] (1.56%). Halloysite typically forms by [[hydrothermal]] alteration of alumino-silicate minerals. <ref>Paul F. Kerr, FORMATION AND OCCURRENCE OF CLAY MINERALS, Clays and Clay Minerals, Volume 1, page 19-32, 1952</ref> It can occur intermixed with [[dickite]], [[kaolin]], [[montmorillonite]] and other clay minerals. [[X-ray diffraction]] studies are required for positive identification. It was first described in 1826 and named for the [[Belgian]] [[geologist]] [[Jean Baptiste Julien d'Omalius d'Halloy|Omalius d'Halloy]]. ==Structure== Two common forms are found, when hydrated the clay exhibits a 1 nm spacing of the layers and when dehydrated (meta-halloysite) the spacing is 0.7 nm. Halloysite naturally occurs as small cylinders which average 30 nm in diameter with lengths between 0.5 and 10 micrometres. <ref>George W. Brindley, STRUCTURAL MINERALOGY OF CLAYS, Clays and Clay Minerals, Volume 1, page 33-43, 1952</ref> ==Geological Occurrence== The formation of halloysite is due to [[hydrothermal]] alteration, and it is often found near [[carbonate rock]]s. For example, halloysite samples found in Wagon Wheel Gap, Colorado, are suspected to be the weathering product of [[rhyolite]] by downward moving waters.<ref>Kerr P. F. (1952) Formation and Occurrence of Clay Minerals Clays and Clay Minerals 1, 19-23</ref> In general the formation of clay minerals is highly favored in tropical and sub-tropical climates due to the immense amounts of water flow. Halloysite has also been found overlaying [[basalt]]ic rock, showing no gradual changes from rock to mineral formation.<ref>Papke K.G. (1970) Halloysite Deposits in the tarraced Hills Washoe County, Nevada Clays and Clay Minerals 19, 2, 71-74</ref> Halloysite occurs primarily in youthful volcanic-derived soils, but it also forms from primary minerals in tropical soils or pre-glacially weathered materials.<ref> Wilson M. J. (1999) The Origin and Formation of Clay Minerals in Soils: Past Present and Future Perspectives Clay Minerals 34, 7-25</ref> Igneous rocks, especially glassy basaltic rocks are more susceptible to weathering and alteration forming halloysite. Often as is the case with halloysite found in [[Juab County, Utah]], the clay is found in close association with [[goethite]] and [[limonite]] and often interspersed with [[alunite]]. [[Feldspar]]s are also subject to decomposition by water saturated with [[carbon dioxide]]. When feldspar occurs near the surface of lava flows, the CO<sub>2</sub> concentration is high, and reaction rates are rapid. With increasing depth, the leaching solutions become saturated with silica, aluminium, sodium, and calcium. Once the solutions are depleted of CO<sub>2</sub> they precipitate as secondary minerals. The decomposition is dependent on the flow of water. In the case that halloysite is formed from [[plagioclase]] it will not pass through intermediate stages.<ref>Kerr P. F. (1952) Formation and Occurrence of Clay Minerals, Clays and Clay Minerals 1, 19-23</ref> ==Applications== A very pure halloysite is mined from an highly altered [[rhyolite]] occurrence in [[New Zealand]] uses include [[porcelain]] and [[bone china]]. <ref>[http://www.halloysite.com/index.htm Home Page<!-- Bot generated title -->]</ref> Various patents exist for the use of hallosyite as nanofillers <ref>US patent #3467618, http://www.google.com/patents?id=tbh0AAAAEBAJ</ref> and in controlled release technology for a range of active agents.<ref>[http://www.azonano.com/news.asp?newsID=1935 Biophan Files Patent on Novel Drug Delivery Using Halloysite Nanotubes<!-- Bot generated title -->]</ref><ref>US patent #5651976, http://www.google.com/patents?KTkcAAAAEBAJ&dq=us+5651976</ref> It is also used for other high-tech [[ceramic]] applications. Halloysite also has been used as a petroleum cracking catalyst in the past, <ref>US Patent #3515682, http://www.google.com/patents?id=Gs8hAAAAEBAJ</ref>. Exxon has also developed a cracking catalyst based on synthetic halloysite<ref>US Patent #4150099, http://www.google.com/patents?id=ROY8AAAAEBAJ</ref>. Due to its structure, it can be used as filler in either natural or modified forms in nanocomposites. ==References== <references/> ==Links== *[http://webmineral.com/data/Halloysite.shtml Webmineral] *[http://www.mindat.org/show.php?id=1808&ld=1&pho= Mindat w/ location data] *[http://www.uwrf.edu/~wc01/halloysite.htm Univ. Wisconsin] *[http://www.reciprocalnet.org/recipnet/showsample.jsp?sampleId=27344589&sampleHistoryId=17234&level=65536&applet=minijamm&setLevel=1 New Zealand halloysite] {{mineral-stub}} [[Category:Phyllosilicates]] [[Category:Aluminium minerals]] [[ca:Halloysita]] [[de:Halloysit-7Å]] [[it:Halloysite]] [[nl:Halloysiet]] [[pl:Haloizyt]] [[ru:Галлуазит]] [[sk:Halloyzit]] [[uk:Галуазит]]