In this work we have systematically replaced OH with F in an amphibole composition intermediate between richterite and pargasite [60% richterite and 40% pargasite in molar proportion; nominal composition Na(Na0.6Ca1.4)(Mg4.6Al0.4)(Si7.2Al0.8)O-22(OH,F)(2)]. Syntheses have been done at 3 kbar P-H2O and 900 degreesC, and for all compositions an assemblage of amphibole plus minor Na-phlogopite has been obtained. Crystal-chemical variations in the amphibole as a function of F have been characterized by a combination of EMPA, X-ray powder diffraction, and infrared spectroscopy. EMPA analyses show that for increasing F in the system (i) the Al-[6] content decreases to 0.13 apfu for the nominal fluorine end-member whereas the Al-[4] content is virtually constant and close to the nominal value; (ii) the fluorine content is systematically lower than expected. The infrared OH-stretching spectra show that those OH-groups locally bonded to (MgMgMg)-Mg-M1-Mg-M1-Mg-M3 configurations are preferentially replaced by F whereas those OH-groups locally bonded to (MgMgAl)-Mg-M1-Mg-M1-Al-M3 configurations are not replaced by F.

DELLA VENTURA, G., Robert, J.L., Sergent, J., Hawthorne, F.C., Delbove, F. (2001). Constraints on F vs. OH incorporation in synthetic [6]Al-bearing monoclinic amphiboles. EUROPEAN JOURNAL OF MINERALOGY, 13, 841-847 [10.1127/0935-1221/2001/0013/0841].

Constraints on F vs. OH incorporation in synthetic [6]Al-bearing monoclinic amphiboles

DELLA VENTURA, Giancarlo;
2001-01-01

Abstract

In this work we have systematically replaced OH with F in an amphibole composition intermediate between richterite and pargasite [60% richterite and 40% pargasite in molar proportion; nominal composition Na(Na0.6Ca1.4)(Mg4.6Al0.4)(Si7.2Al0.8)O-22(OH,F)(2)]. Syntheses have been done at 3 kbar P-H2O and 900 degreesC, and for all compositions an assemblage of amphibole plus minor Na-phlogopite has been obtained. Crystal-chemical variations in the amphibole as a function of F have been characterized by a combination of EMPA, X-ray powder diffraction, and infrared spectroscopy. EMPA analyses show that for increasing F in the system (i) the Al-[6] content decreases to 0.13 apfu for the nominal fluorine end-member whereas the Al-[4] content is virtually constant and close to the nominal value; (ii) the fluorine content is systematically lower than expected. The infrared OH-stretching spectra show that those OH-groups locally bonded to (MgMgMg)-Mg-M1-Mg-M1-Mg-M3 configurations are preferentially replaced by F whereas those OH-groups locally bonded to (MgMgAl)-Mg-M1-Mg-M1-Al-M3 configurations are not replaced by F.
2001
DELLA VENTURA, G., Robert, J.L., Sergent, J., Hawthorne, F.C., Delbove, F. (2001). Constraints on F vs. OH incorporation in synthetic [6]Al-bearing monoclinic amphiboles. EUROPEAN JOURNAL OF MINERALOGY, 13, 841-847 [10.1127/0935-1221/2001/0013/0841].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11590/145987
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