Crystal chemistry of the microporous tellurite minerals zemannite and kinichilite, Mg0.2 [Me (super 2+) Fe (super 3+) (TeO (sub 3) ) (sub 3) ] . 4.5H (sub 2) O, (Me (super 2+) = Zn;Mn)

Chemical and structural re-investigation of these microporous tellurite minerals revealed the arrangement of the non-framework atoms and led to the revision of their chemical formulae to Mg (sub 0.5) [ZnFe (super 3+) (TeO (sub 3) ) (sub 3) ]<P6M><P255>4.5H (sub 2) O (zemannite) and Mg (sub 0.5) [Mn (super 2+) ,Zn)Fe (super 3+) (TeO (sub 3) ) (sub 3) ]<P6M><P255>4.5H (sub 2) O (kinichilite). Only negligible amounts of Na (sub 2) O were found, though Na had earlier been assumed to play an important role. Instead of Na (super +) ions, octahedrally coordinated [Mg(H (sub 2) O) (sub 6) ] (super 2+) complexes and 'free' water molecules arranged in a hydrogen-bonded network were located within the tubular channeels of the [(Zn,Mn) (super 2+) Fe (super 3+) (TeO (sub 3) ) (sub 3) ] (super -) framework. A reasonable [Mg (super [6]) (H (sub 2) O) (sub 6) (H (sub 2) O) (sub 3) ] (super 2+) ordering scheme with the reduced symmetry 3 instead of 6 (sub 3) /m was deduced for each single channel; this violates the P6 (sub 3) /m framework symmetry. Moessbauer spectroscopy showed that the iron in zemannite and kinichilite is entirely octahedrally coordinated Fe (super 3+) . Therefore the presence of additional hydrogen for charge balance, as stated in the original formulae, is unnecessary. Considerable contents of Fe (sub 2) O (sub 3) were determined for both zemannite and kinichilite, and only the different contents of Zn and Mn allows their distinction.