T10 Mineral Evolution and Ecology: Potential Directions for the Next 100 Years with the Mineralogical Society of America

Sunday, 4 November 2018
8:00 AM - 12:00 PM
Room 233

THERMODYNAMICS AND CRYSTALLOGRAPHIC COMPLEXITY OF SODIUM URANYL SULFATE MINERALS WITH UNIQUE TOPOLOGIES

Paper number: T10-8
Program: Technical Sessions
Time: 9:50 AM – 10:05 AM

Authors

Abstract

Although historically few uranyl sulfates have been described1, more than 30 new uranyl sulfates have been discovered within the past 10 years1, with 22 of these new species found exclusively within the White Canyon mines of southwestern Utah1,2. The uranyl sulfate group has been poorly thermodynamically characterized3, resulting in a lack of understanding regarding their formation mechanisms. These phases share the same chemistry, but differ in water content, crystal symmetry and crystal complexity, implying underlying subtleties to their formation.

This project has undertaken the synthesis, characterization and calorimetric analysis of the White Canyon suite of sodium uranyl sulfates and their closely-related synthetic phases. Pure synthetic analogs were crystallized through evaporation in isotherm ovens from solutions of U, Na and S. The resulting phases were fully characterized with single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), scanning electron microscope (SEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), and thermogravimetric analysis (TGA). The ground crystals were pressed into ~5 mg pellets and dropped into an AlexSys high-temperature 3D Calvet-type calorimeter to measure the enthalpy of solution, from which the enthalpy of formation (ΔH°f ) was determined4. Finally, the structural complexity of each phase was calculated using the ToposPro package5,6.

Our results have found that structural complexity is strongly correlated with the ΔH°f of the phases, implying the formation mechanism is energetic rather than entropic in nature. Continuing work will focus on the synthesis of additional sodium uranyl sulfates and determining whether the correlation between complexity and stability extends to other uranium groups.

References:

1IMA Mineral List Database. Available online: http://rruff.info/ima/ (accessed 12 August 2018).

2Olds, et al. Mineralogical Magazine. (2018) 1-30.

3J. Plášil. (2014) J. Geosci. 59: 99-114.

4A. Navrotsky. (2014) J. Am. Ceram. Soc. 97: 3349-3359.

5V.A. Blatov et al. (2014) Cryst. Growth Des. 14: 3576–3586.

6S.V. Krivovichev. (2016) Acta Cryst. B72: 274-276.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-321865

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