Molecular structural studies of the amorphous mineral pitticite Fe, AsO4, SO4, H2O

Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the assessment of the structure of these types of mineral. Among this group of minerals is pitticite simply described as Fe, AsO4, SO4, H2O. The objective of this research is to determine the molecular structure of the mineral pitticite using vibrational spectroscopy. Raman microscopy offers a useful method for the analysis of such colloidal minerals.Raman and infrared bands are attributed to the AsO43-, SO42- and water stretching vibrations. The Raman spectrum is dominated by a very intense sharp band at 983 cm−1 assigned to the SO42- symmetric stretching mode. A strong Raman band at 1041 cm−1 is observed and is assigned to the SO42- antisymmetric stretching mode. Low intensity Raman bands at 757 and 808 cm−1 may be assigned to the AsO43- antisymmetric and symmetric stretching modes. Raman bands observed at 432 and 465 cm−1 are attributable to the doubly degenerate ν2 (SO4)2− bending mode.