The Geology, Mineralogy and Exploitation of Halloysite Clays of Northland, New Zealand
Colin C. Harvey, Haydn H. Murray, 1993. "The Geology, Mineralogy and Exploitation of Halloysite Clays of Northland, New Zealand", Kaolin Genesis and Utilization, Haydn H. Murray, Wayne M. Bundy, Colin C. Harvey
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In Northland, New Zealand, several large deposits of hydrated halloysite clay have been formed by the in situ alteration of rhyolite volcanics of Pliocene or Pleistocene age. The rhyolites were erupted through pre-Pliocene sedimentary strata and locally through basalt. They are onlapped in places by more recent basalt flows. The halloysite clays have been formed from both hydrothermal alteration and sub-tropical weathering.
The clays are mined by open-pit methods and processed by crushing and fractionation to a product of 98% finer than 2 μm particle size, which is of exceptional whiteness and brightness. The unique properties of these halloysites has led to their world wide utilisation in specialised ceramic applications.