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Mineralogical Magazine; June 2006; v. 70; no. 3; p. 299-307; DOI: 10.1180/0026461067030333
© 2006 Mineralogical Society of Great Britain and Ireland
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An XRD, SEM and TG study of a uranopilite from Australia

R. L. Frost1,*, M. L. Weier1, G. A. Ayoko1, W. Martens1 and J. Cejka2

1 Inorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia
2 National Museum, Václavské námestí 68, CZ-115 79 Praha 1, Czech Republic

* E-mail: r.frost{at}qut.edu.au

A uranopilite from The South Alligator River, Northern Territory, Australia, has been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with EDAX attachment, and thermogravimetry in conjunction with evolved gas mass spectrometry. The XRD shows that the mineral is a pure uranopilite with few if any impurities. The SEM images show that the uranopilite consists of elongated crystals, up to 50 µm long and 5 µm wide. Thermogravimetry combined with mass spectrometry shows that dehydration occurs at ~31°C resulting in the formation of metauranopilite. The first dehydration step over 20–71°C corresponds to a decrease of 5.4 wt.%, equivalent to 6.076 H2O. The second dehydration step, over the temperature range 71–162.4°C corresponds to a decrease of 4.7 wt.%, equivalent to 5.288 H2O, making a total of 11.364 moles of H2O, close to 12 H2O for uranopilite.

Dehydroxylation takes place over the temperature range 80–160°C. The loss of sulphate occurs at higher temperatures in two steps at 622 and 636°C. A mass loss also occurs at 755°C, accounted for by evolved oxygen.

KEYWORDS: uranopilite, johannite, zippeite, uranyl sulphate minerals, dehydroxylation, dehydration, infrared spectroscopy, Raman spectroscopy






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