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Discovery of halloysite books in altered silicic Quaternary tephras, northern New Zealand

Published online by Cambridge University Press:  02 January 2018

M.J. Cunningham ,
D.J. Lowe ,
J.B. Wyatt ,
V.G. Moon  and
G. Jock Churchman
M.J. Cunningham
Affiliation:
School of Science, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand
D.J. Lowe*
Affiliation:
School of Science, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand
J.B. Wyatt
Affiliation:
School of Science, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand
V.G. Moon
Affiliation:
School of Science, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand
G. Jock Churchman
Affiliation:
School of Science, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand
*
*E-mail: [email protected]
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Abstract

Hydrated halloysite was discovered in books, a morphology previously associated exclusively with kaolinite. From ∼1.5 to ∼1500 μm in length, the books showed significantly greater mean Fe contents (Fe2O3 = 5.2 wt.%) than tubes (Fe2O3 = 3.2 wt.%), and expanded rapidly with formamide. They occurred, along with halloysite tubes, spheroids and plates, in highly porous yet poorly permeable, silt-dominated, Si-rich, pumiceous rhyolitic tephra deposits aged ∼0.93 Ma (Te Puna tephra) and ∼0.27 Ma (Te Ranga tephra) at three sites ∼10–20 m stratigraphically below the modern landsurface in the Tauranga area, eastern North Island, New Zealand. The book-bearing tephras were at or near saturation, but have experienced intermittent partial drying, favouring the proposed changes: solubilized volcanic glass + plagioclase→halloysite spheroids→halloysite tubes→halloysite plates→ halloysite books. Unlike parallel studies elsewhere involving both halloysite and kaolinite, kaolinite has not formed in Tauranga presumably because the low permeability ensures that the sites largely remain locally wet so that the halloysite books are metastable. An implication of the discovery is that some halloysite books in similar settings may have been misidentified previously as kaolinite.

Keywords

halloysiteclay morphologyFe contentpyroclastictephrochronologyTe Ranga tephraTe Puna tephraQuaternary
Type
Research Article
Information
Clay Minerals , Volume 51 , Issue 3 , June 2016 , pp. 351 - 372
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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Footnotes

†

Current address: Waikato Regional Council, Private Bag 3038, Hamilton 3240, New Zealand.

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