Beitrag
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 Literaturangaben
veröffentlicht: Jun 5, 1991
Manuskript akzeptiert: Jan 25, 1991
Manuskript erhalten: Oct 16, 1990
DOI: 10.1127/ejm/3/3/0575
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
narsarsukite (Zr-bearing) •
Mossbauer •
FTIR •
crystal chemistry •
Sirwa Massif (Morocco)
Schlagworte