CRYSTAL-CHEMISTRY OF THE MICROPOROUS TELLURITE MINERALS ZEMANNITE ANDKINICHILITE, MG0.5[ME2+FE3+(TEO3)3].4.5H2O, (ME2+=ZN MN)

Chemical and structural re-investigations of the microporous tellurite minerals zemannite and kinichilite revealed the previously undetermin ed arrangement of the non-framework atoms and led to the revision of t heir chemical formulas to Mg0.5[ZnFe3+(TeO3)3].4.5H2O (zemannite) and Mg0.5[(Mn2+,Zn)Fe3+(TeO3)3].4.5H2O (kinichilite). Crystal-structure in vestigations using single-crystal X-ray diffraction, electron micropro be and energy-dispersive X-ray analyses, as well as thermogravimetric and IR spectroscopic investigations were carried out on crystals from the type localities in Mexico (Moctezuma Mine) and Japan (Kawazu Mine) , respectively. Only neglectably small amounts of Na2O have been found , although sodium was before assumed to be a significant part of the c omposition of both minerals. Instead of Na+ ions octahedrally coordina ted [Mg(H2O)6]2+ complexes and 'free' water molecules arranged in a hy drogen-bonded network were located within the tubular channels of the [(Zn,Mn)2+Fe3+(TeO3)3]- framework. A reasonable were located within th e tubular channels of the [(Zn,Mn)2+Fe3+(TeO3)3]- framework. A reasona ble [Mg[6](H2O)6(H2O)3]2+ ordering-scheme with the reduced symmetry 3 instead of 6(3)/m was deduced for each single channel; this violates t he P6(3)/m framework symmetry. Mossbauer spectroscopy showed that the iron in zemannite and kinichilite is entirely octahedrally coordinated Fe3+. Therefore the presence of additional hydrogen for charge balanc e, as stated in the original formulas of zemannite and kinichilite, is unnecessary. Considerable Fe2O3 contents were determined for both zem annite and kinichilite and only the different contents of Zn and Mn al low them to be distinguished between the two species.