A Raman spectroscopic study of selected natural jarosites.

Raman spectroscopy has been used to characterise the jarosite group of minerals of formula Mn(Fe3+)6(SO4)4(OH)12 where M may be K, (NH4)+, Na, Ag or Pb and where n = 2 for monovalent cations and 1 for the divalent cations. Raman spectroscopy proved useful for mineral identification especially where closely related minerals crystallise out from solutions where paragenetic relationships exist between the minerals. The band position of the SO4(2-) symmetric stretching mode proved to be a function of the ionic radius of the cation. The bending modes show a slight dependence. The spectra of the natural samples can be complex. This complexity is attributed to the incorporation of low levels of other cations into the structure.