The Mineral Nealite Pb₄Fe²⁺(AsO₃)₂Cl₄ · 2H₂O—A Raman Spectroscopic Study

ABSTRACT

The mineral nealite Pb₄Fe²⁺(AsO₃)₂Cl₄ · 2H₂O is of archaeological significance as it is man made mineral formed through the dumping of mine wastes in the sea. The mineral has been studied by Raman spectroscopy. Raman spectroscopy identifies intense Raman bands at 708 and 732 cm⁻¹ assigned to stretching vibrations. In addition low intensity bands are observed at 604 and 632 cm⁻¹, which are attributed to symmetric and antisymmetric stretching modes. Low intensity Raman band is observed at 831 cm⁻¹ and is assigned to the stretching vibration. Intense Raman bands at 149 and 183 cm⁻¹ are attributed to M-Cl stretching vibrations. Raman spectroscopy identifies arsenic anions in different oxidation states in the mineral. The molecular structure of the mineral nealite, as indicated by Raman spectroscopy, is more complex than has been reported by previous studies.

KEYWORDS:

• archaeology
• arsenite
• nealite
• Raman spectroscopy

ACKNOWLEDGMENTS

The financial and infra-structure support of the Queensland University of Technology Chemistry Discipline, Faculty of Science and Technology is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the instrumentation.