1 Raman spectroscopy of halotrichite from Jaroso , Spain

Raman spectroscopy complimented with infrared ATR spectroscopy has been used to characterise a halotrichite FeSO4.Al2(SO4)3.22H2O from The Jaroso Ravine, Almeria, Spain. Halotrichites form a continuous solid solution series with pickingerite and chemical analysis shows that the jarosite contains 6% Mg. Halotrichite is characterised by four infrared bands at 3569.5, 3485.7, 3371.4 and 3239.0 cm. Using Libowitzky type relationships, hydrogen bond distances of 3.08, 2.876, 2.780 and 2.718 Å were determined. Two intense Raman bands are observed at 987.7 and 984.4 cm and are assigned to the ν1 symmetric stretching vibrations of the sulphate bonded to the Fe and the water units in the structure. Three sulphate bands are observed at 77 K at 1000.0, 991.3 and 985.0 cm suggesting further differentiation of the sulphate units. Raman spectrum of the ν2 and ν4 region of halotrichite at 298 K shows two bands at 445.1 and 466.9 cm, and 624.2 and 605.5 cm respectively confirming the reduction of symmetry of the sulphate in halotrichite.