Halloysite
Halloysite is also in the kaolin group of clay minerals along with kaolinite. It occurs as platelets similar to kaolinite with a chemical formula of Al2Si2O5(OH)4 • 2H2O. The difference from kaolinite is the non-structural water that represents a monolayer of water molecules intercalated between the aluminosilicate layers, a 10 Å thickness in the halloysite with the water layer and a 7 Å thickness in the kaolinite without the water layer. The hydrated halloysite converts spontaneously and irreversibly into a less hydrous form when dried and like kaolinite, reverts to an aluminosilicate layer thickness layer of 7 Å. However, imperfections in the crystal lattice of the halloysite causes a misfit between different aluminosilicate layers, but due to interference of the interlayer of water, these imperfections cause the halloysite platelet to roll up into a tubular form (halloysite nanotubes or HNTs). These tubes are elongate and can be as long as 10 microns. The diameter of the tubes are on the order of 10's of nanometers, thus establishing a measurement of a highly acicular mineral on a nanometer scale of size. These two properties are highly sought after in the nanotechnology field.Uses
Halloysite has historically been used in the manufacture of porcelain, bone china, and fine china due to purity of the clay and the low iron and titania content result in ceramic ware with exceptional whiteness and translucency. Its fine particle size enables halloysite to also be used as a suspension agent in glaze preparations as well as in filters and inkjets, and as an ingredient in special paints applied to ships to prevent barnacles from growing on the ships' hulls.
HNTs can be coated with metallic and other substances to achieve a wide variety of electrical, chemical, and physical properties. The hollow tube of HNTs can be filled with a variety of active ingredients including those used for cosmetics, household and personal care products, pesticides, pest repellents, pharmaceuticals and other agents that could benefit from extended release. Preliminary work completed by i-minerals indicates the HNTs from the WBL Pit area have the lowest levels of trace elements when compared with HNTs from several halloysite deposits around the world. This gives the company an initial leg up on meeting the stringent requirements of the pharmaceutical and cosmetic industries.
