Halloysite

From a purely physical properties point-of-view, halloysite is a clay mineral similar to kaolin in firing and raw appearance. In fact, it normally occurs with kaolin deposits because kaolin is the precursor mineral. Applied Minerals describes it this way: "Halloysite is chemically identical to kaolin clay (Al2Si2O5(OH)4 x nH₂O) with one layer of water molecules existing between layers of alumina and silica. Formation occurs when kaolin sheets roll into tubes due to the strain caused by a lattice mismatch between the adjacent silicon dioxide and aluminum oxide layers. This is a process that occurs over millions of years under extremely rare conditions." Imerys says this: "Halloysite is an aluminosilicate clay mineral with the same chemical formula as kaolin Al2Si2O5(OH)4 2H₂O but with water (H₂O) intercalated in its clay structure."

Halloysites can often be employed in high quality porcelain recipes interchangeably (depending on purity and amount of iron). Some clays referred to as halloysite just contain a small percentage of the actual mineral (Helmer Kaolin is an example). It seems obvious that kaolin, having a flat particle shape, should theoretically be much more plastic. But in practice the plasticities of various halloysites are comparable with kaolins of the same iron content. While it is also intuitive that halloysites would have lower shrinkages, they actually shrink more, both in drying and firing.

Commercial halloysites of exceptional purity and fired whiteness are available. The unique particle shape of the material make it useful for a wide range of non-ceramic uses, in fact only a small percentage is used in ceramics.

Related Information

Compare powder color of super white kaolins

These three materials also fire to a similar color. Grolleg is the most plastic, Dragonite the least.

Halloysite particle shapes (left) vs. Kaolinite (right)

Halloysite forms over long periods as kaolin sheets roll into tubes.

Links

Typecodes	Clay Minerals The property of plasticity is evident in a wide array of materials of different mineralogy. In addition, many minerals are considered parent minerals to clays, they weather down to become these clays.
Materials	New Zealand Halloysite The whitest burning kaolin we have ever seen. It is very sticky when wet, suspends glazes well & makes super white porcelain (with help from a white bentonite).
Materials	Plainsman Troy Clay
Materials	Dragonite Halloysite
URLs	http://www.minersoc.org/pages/gallery/claypix/halloysite/halloysite7g.html One of many halloysite micrographs at minersoc.org
URLs	http://en.wikipedia.org/wiki/Halloysite Halloysite at Wikipedia
URLs	http://www.handbookofmineralogy.org/pdfs/Halloysite.pdf Halloysite mineral data
URLs	https://www.imerys.com/minerals/halloysite Imerys Halloysite Information Page They are promoting this for the tableware industry. They claim high whiteness and translucency, tubular structure, nanosize, high aspect ratio, low iron and titanium content.
URLs	http://webmineral.com/data/Halloysite.shtml Halloysite at WebMineral.com
Glossary	Clay What is clay? How is it different than dirt? For ceramics, the answer lies on the microscopic level with the particle shape, size and how the surfaces interact with water.

By Tony Hansen
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