Journal of the Royal Society of New Zealand abstracts

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Structural studies of New Zealand pounamu using Mössbauer spectroscopy and electron paramagnetic resonance

W. Craighead Tennant^1*, Rodney F. C. Claridge¹, Catherine A. McCammon², Alex I. Smirnov³, and Russell J. Beck⁴

¹Chemistry Department, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand. craig.tennant@canterbury.ac.nz
²Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany.
³Department of Chemistry, North Carolina State University, Campus Box 8204, Raleigh, NC 27695, USA.
⁴27 Chelmsford Street, Invercargill, New Zealand.

Abstract  We report Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy (EPR) studies of a number of New Zealand minerals that can be classified under the non-specific names “pounamu” or “greenstone”. Mössbauer measurements allowed the distribution of iron in its +2 and +3 oxidation states to be assigned to the M1 to M4 sites of the constituent minerals, tremolite-actinolite in the case of nephrite jades. EPR at two frequencies, 9.4 GHz (X-band) and 94.1 GHz (W-band), allowed the determination of the distribution of Mn²⁺ in these sites. The results are apparently contrary to the usual assignments made for the parent minerals tremolite and actinolite. In two cases, one a nephrite jade and the other a serpentine, significant quantities of magnetically ordered minerals chalcopyrite and magnetite were identified by Mössbauer spectroscopy. These minerals could not be found in the X-ray diffraction patterns of the same minerals leading to the conclusion that they are very finely divided in the samples studied.

Keywords  pounamu; greenstone; Mössbauer spectroscopy; electron paramagnetic resonance

This paper continues a study initiated by the late Professor Cuthbert J. Wilkins. It is to his memory that the paper is dedicated.

R05003 Received 21 January 2005; accepted 21 April 2005; Online publication date 6 December 2005
Journal of the Royal Society of New Zealand
Volume 35, Number 4, December, 2005, pp 385–398

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