Original paper

Crystal chemistry of narsarsukite

Wagner, Christiane; Parodi, Gian Carlo; Semet, Michel; Robert, Jean-Louis; Berrahma, M'hamed; Velde, Danielle

European Journal of Mineralogy Volume 3 Number 3 (1991), p. 575 - 586

25 references

published: Jun 14, 1991
manuscript accepted: Jan 25, 1991
manuscript received: Oct 16, 1990

DOI: 10.1127/ejm/3/3/0575

BibTeX file

ArtNo. ESP147050303010, Price: 29.00 €

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Abstract

Abstract The finding of Zr-rich narsarsukite in a peralkaline lava from Morocco prompted a re-evaluation of the crystal chemistry of this mineral. Microprobe analyses show that F is present in narsarsukite from all known occurrences. An examination of two specimens (from Narsarsuk and Montana) by Mossbauer spectroscopy indicates that most of the iron is present in the trivalent state. The infrared spectra of three specimens exhibit four absorption bands in the 4000-3000 cm-1 range. The assignment of these bands either to hydroxyls or water molecules is discussed, the latter hypothesis being favoured. Significantly larger unit-cell parameters in the Moroccan sample are compatible with the extensive replacement of Ti by Zr. The entry of F in the structure is coupled with the replacement of Ti by Fe3+, F substituting the underbonded apical oxygens of the TiO6 octahedra. These new results suggest that the general formula Na2 [(Ti,Zr)(1-x)Fex3+] O(1-x)FxSi4O10-(0-1/2)H2O, with 0

Keywords

narsarsukite (Zr-bearing)MossbauerFTIRcrystal chemistrySirwa Massif (Morocco)