A Raman spectroscopic study of copiapites Fe2+Fe3+(SO4)6(OH)2 · 20H2O: environmental implications

Authors

  • Ray L. Frost

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    1. Department of Chemistry, Faculty of Science and Technology, Queensland University of Technology, Brisbane, Queensland 4001, Australia
    • Department of Chemistry, Faculty of Science and Technology, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4001, Australia.
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Abstract

Raman spectroscopy has been used to study selected mineral samples of the copiapite group. Copiapite (Fe2+Fe3+(SO4)6(OH)2 · 20H2O) is a secondary mineral formed through the oxidation of pyrite. Minerals of the copiapite group have the general formula AFe4(SO4)6(OH)2 · 20H2O, where A has a + 2 charge and can be either magnesium, iron, copper, calcium and/or zinc. The formula can also be B2/3Fe4(SO4)6(OH)2 · 20H2O, where B has a + 3 charge and may be either aluminium or iron. For each mineral, two Raman bands are observed at around 992 and 1029 cm−1, assigned to the (SO4)2−ν1 symmetric stretching mode. The observation of two bands provides evidence for the existence of two non-equivalent sulfate anions in the mineral structure. Three Raman bands at 1112, 1142 and 1161 cm−1 are observed in the Raman spectrum of copiapites, indicating a reduction of symmetry of the sulfate anion in the copiapite structure. This reduction in symmetry is supported by multiple bands in the ν2 and ν4(SO4)2− spectral regions. Copyright © 2010 John Wiley & Sons, Ltd.

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