IMA 2018-A = crystal structure determination and redefinition of eztlite

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Marco E. Ciriotti
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IMA 2018-A = crystal structure determination and redefinition of eztlite

Messaggio da Marco E. Ciriotti » ven 18 mag, 2018 17:50

Prossima pubblicazione.

Referenza:
▪ Missen, O.P., Mills, S.J., Spratt, J., Welch, M.D., Birch, W.D., Rumsey, M.S., Vylita, J. (2018): The crystal structure determination and redefinition of eztlite, Pb2+2Fe3+3(Te4+O3)3(SO4)O2Cl. Mineralogical Magazine, 82, (in press).
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24913
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: IMA 2018-A = crystal structure determination and redefinition of eztlite

Messaggio da Marco E. Ciriotti » sab 10 nov, 2018 13:29

Referenza:
▪ Missen, O.P., Mills, S.J., Spratt, J., Welch, M.D., Birch, W.D., Rumsey, M.S., Vylita, J. (2018): The crystal structure determination and redefinition of eztlite, Pb2+2Fe3+3(Te4+O3)3(SO4)O2Cl. Mineralogical Magazine, 82, (in press).

Abstract:
The crystal structure of eztlite has been determined using single-crystal synchrotron X-ray diffraction and supported using electron microprobe analysis and powder diffraction. Eztlite, a secondary tellurium mineral from Moctezuma mine, Mexico, is monoclinic, space group Cm, with a = 11.466(2) Å, b = 19.775(4) Å, c = 10.497(2) Å, β = 102.62(3)° and V = 2322.6(9) Å3. The chemical formula of eztlite has been revised to Pb2+2Fe3+3(Te4+O3)3(SO4)O2Cl from that stated by Williams (1982) as Fe3+6Pb2+2(Te4+O3)3(Te6+O6)(OH)10·nH2O. This change has been accepted by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association, Proposal 18-A. Eztlite was reported to be a mixed-valence Te oxysalt; however the crystal structure, bond valence analysis and charge balance considerations clearly show that all Te is tetravalent. Eztlite contains a unique combination of elements and is only the second Te oxysalt to contain both sulphate and chloride. The crystal structure of eztlite contains mitridatite-like layers, with a repeating triangular nonameric [Fe3+9O36]45- arrangement formed by nine edge-sharing Fe3+O6 octahedra, decorated by four trigonal pyramidal Te4+O3 groups, compared with PO4 or AsO4 tetrahedra in mitridatite-type minerals. In eztlite, all four tellurite groups associated with one nonamer are orientated with the lone pair of the Te atoms pointing in the same direction, whereas in mitridatite the central tetrahedron is orientated in the opposite direction to the others. In mitridatite-type structures, interlayer connections are formed exclusively via Ca2+ and water molecules, whereas the eztlite interlayer contains Pb2+, sulphate tetrahedra and Cl-. Interlayer connectivity in eztlite is achieved primarily by connections via the long bonds of Pbφ8 and Pbφ9 groups to sulphate tetrahedra and to Cl-. Secondary connectivity is via Te–O and Te–Cl bonds.
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