The OH-F substitution in synthetic pargasite at 1.5 kbar, 850 °C.

Jean-Louis Robert (1) , Giancarlo Della Ventura (2) , Mark D. Welch (3) , Franck C. Hawthorne (4)

1 ISTO - Institut des Sciences de la Terre d'Orléans
2 Dipartimento di Scienze Geologiche [Roma TRE]
3 Department of Mineralogy
4 DEPARTMENT OF GEOLOGICAL SCIENCES - Department of Geological Sciences

Amphiboles were synthesized at 1.5 kbar PH2O and 850 °C along the join pargasite-fluoropargasite. Structural variations in the amphibole as a function of F have been characterized by a combination of SEM-EDS, X-ray powder diffraction, and infrared spectroscopy. SEM-EDS analyses show that, for increasing F in the system, there is a decrease in Altot in the amphibole and a significant decrease of F incorporation in the structure. In agreement with the EDS data, the variation in cell parameters and IR spectra show that incorporation of F in pargasite is restricted to about 1.0 atoms per formula unit (apfu). The OH-stretching spectra show fine structure caused by F replacing OH at the O3 anion site, and are consistent with two-mode behavior typical of A-site-filled amphiboles. The agreement between calculated and observed relative band intensities suggests complete short-range disorder of OH and F at the O3 anion site.

Domains: Geochemistry

Jean-Louis Robert, Giancarlo Della Ventura, Mark D. Welch, Franck C. Hawthorne. The OH-F substitution in synthetic pargasite at 1.5 kbar, 850 °C.. American Mineralogist, 2000, 85, pp.926-931. ⟨hal-00077556⟩