Crystal-chemical study of ecdemite from Harstigen

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Marco E. Ciriotti
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Crystal-chemical study of ecdemite from Harstigen

Messaggio da Marco E. Ciriotti » dom 14 apr, 2019 11:14

Prossima pubblicazione.

Referenza:
▪ Perchiazzi, N., Hålenius, U., Vignola, P., Demitri, N. (2019): Crystal-chemical study of ecdemite from Harstigen, a new natural member of the layered lead oxyhalides group. European Journal of Mineralogy, 31, (in press).

Abstract:
Ecdemite from Harstigen, Värmland, Central Sweden, was studied through Raman and FTIR spectroscopy, electron-microprobe techniques, synchrotron powder and single-crystal diffraction. The ideal mineral formula proposed by Palache, Pb6Cl4As2O7, is confirmed. In contrast to previous suggestions, however, the present study demonstrates that the mineral is monoclinic, with space-group type P21 and unit-cell parameters a = 10.828(4) Å, b = 10.826(2) Å, c = 6.970(1) Å, β = 113.26°(2). The crystal-structural study of ecdemite shows that the mineral can be considered as made up of regularly alternating Cl layers and litharge-like defective layers, also hosting As cations, with the representative formula {Pb2[Pb4O](AsO3)2}4+, in a 1:1 ratio. These features indicate that ecdemite can be considered as a new member of the layered lead oxyhalides group.

NdR: Dal solo abstract nulla si precisa se l'ecdemite è un polimorfo (o no) della heliophyillite e se quest'ultima è (oppure no) una valida specie minerale. Probabilmente nel testo ci saranno ulteriori informazioni.
Marco E. Ciriotti

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