Raman spectroscopic vibrational analysis of the complex iron sulfates clairite, metavoltine, and voltaite from the burning coal dump Anna I, Alsdorf, Germany
Abstract
Vibrational spectroscopy has been used to characterize the three uncommon complex iron sulfates clairite, (NH4)(2)Fe(3)(SO4)(4)(OH)(3)3H2O, metavoltine, Na(6)K(2)Fe(2+)Fe(6)(3+)(SO4)(12)O(2) . 18H2O, and voltaite, K(2)Fe(5)(2+)Fe(3)(3+)Al(SO4)(12) . 18H2O. The investigated specimens were formed at the burning coal dump Anna I (Alsdorf, Germany) due to alteration processes connected with the subsurface thermal activity.
It is found that all three minerals display complex Raman spectra with an extensive proliferation of bands attributed to the sulfate vibrational modes. Both clairite and metavoltine show extraordinary strong Raman bands in the low-wavenumber region, which can be attributed to the Fe-O stretching modes.
Clairite and metavoltine show a very similar spectral shape; it can be concluded that both minerals can exhibit a similar crystal structure. In comparison, voltaite represents a different structural type; therefore, a distinct Raman spectrum is observed.