Crystal structure and iron topochemistry of erionite-K from Rome, Oregon, U.S.A

A complete crystal-chemical characterization of erionite-K from Rome, Oregon, was obtained by combining field emission scanning electron microscopy, laboratory parallel-beam transmission powder diffraction, and [sup.57]Fe Mossbauer spectroscopy. Rietveld refinement results evidenced that the most striking difference in comparison with the structure of erionite-Ca is significant K at a K2 site (1/2, 0, 0), which is empty in erionite-Ca. In addition, site Cal shows low occupancy and Ca3 is vacant. The oxidation and coordination state of Fe, whose occurrence was revealed by chemical analysis, have been clarified by exploiting room- and low-temperature [sup.57]Fe Mossbauer spectroscopy. The majority of Fe (95%) was attributed to [Fe.sup.3+]-bearing, superparamagnetic, oxide-like nanoparticles with dimensions between 1 and 9 nm, and the remaining 5% was attributed to hematite particles with size [greater than or equal to] 10 nm, both located on the crystal surface. Keywords: Oregon erionite, erionite-K, crystal structure, iron topochemistry, field emission, scanning electron microscopy, laboratory parallel-beam transmission powder diffraction, Rietveld refinement, [sup.57]Fe Mossbauer spectroscopy