Spectroscopic and magnetic studies of ferric iron hydroxy sulfates: the series Fe(OH)SO_4·nH_2O and the jarosites

Abstract

Optical and infrared absorption and magnetic susceptibility data are reported for the ferric iron hydroxy sulfate minerals and compounds: basic iron sulfate, Fe(OH)SO_4; butlerite, Fe(OH)SO_4.2H2_O; parabutlerite, Fe(OH)SO4_.2H_2O; fibroferrite, Fe(OH)SO_4.5H_2O; jarosite, KFe_3(SO_4)_2(OH)_6; and stewartite, MnFe_2(H_2O)_6(OH)_2(PO_4)_2. The relationships among intensity of color, indices of refraction, pleochroism, anti ferromagnetic interaction among Fe^(3+) ions, and structure are discussed for 7 Ā corner-linked chain structures and the two-dimensional Fe^(3+) sheets of the jarosites. For all of these compounds the greatest intensity of the Fe^(3+) absorption bands and the highest refractive index occur when the vibration direction of the incident light is aligned with the cation chains or in the plane of the jarosite sheets. The ligandfield absorption band intensities of all of these compounds are enhanced up to two orders of magnitude above what they are in magnetically dilute compounds.

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