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Halloysite
From Wikipedia, the free encyclopedia
Halloysite is a clay mineral with the empirical formula Al2Si2O5(OH)4. Its main constituents are aluminium (20.90%), silicon (21.76%), and hydrogen (1.56%). Halloysite typically forms by hydrothermal alteration of alumino-silicate minerals. 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 Omalius d'Halloy.
A very pure halloysite is mined from an highly altered rhyolite occurrence in New Zealand and used for making porcelain, bone and fine china. The largest deposit in the western hemisphere is at the Dragon Mine in Utah where the deposit consists of primarily high aspect ratio tubules used for nanofillers and in controlled release technology for a range of active agents. It is also used for other high-tech ceramic applications. Other commercial deposits are found in Turkey and China.
Halloysite also has potential uses in nano technology due to its nanotube structuring. Unlike other nanostructured clays that must be exfoliated, halloysite naturally occurs as small cylinders which average 30 nm in diameter with lengths between 0.5 and 10 microns. Halloysite nanotubes are commonly used in controlled release applications, for inclusion in plastics composites and may be coated with metal by electroless plating techniques to make conductive fillers.
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