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Synthesis and water contents of Fe (super 2+) -bearing cordierites

C. Boberski and W. Schreyer
Synthesis and water contents of Fe (super 2+) -bearing cordierites
European Journal of Mineralogy (October 1990) 2 (5): 565-584


Cordierites with compositions ranging from the Mg- to the Fe (super 2+) -end member were synthesized hydro thermally at 700 degrees C/2 kbar/3 days or 650 degrees C/1.5 kbar/ 3 days under the oxygen fugacity of the wuestite/iron buffer. Mossbauer spectra indicate that Fe (super 2+) occupies only the octahedral site M in the cordierite structure. In ESR-spectra no Fe (super 3+) was detected. The mean refractive index n (sub m) of the dehydrated synthetic cordierites increases linearly with F = Fe (super 2+) /(Fe (super 2+) + Mg). The additional increase of n (sub m) with rising water contents for Fe (super 2+) -bearing cordierites cannot be distinguished from that for pure Mg-cordierite because of the blurring effect of water-bearing voids in all cordierites synthesized hydrothermally. Cell edges a and b increase, whereas c decreases linearly with increasing F. For a given F, cell volume is independent of water content. Based on IR-data, the synthetic MgFe-cordierites are Al,Si ordered. Their distortion indices Delta vary from 0.22 degrees to 0.29 degrees . Infrared spectra show molecular water only with orientation of the H-H vector parallel to the crystallographic c-axis (Type I), which is typical for cordierites with no cations in the channel. Mg-cordierite was hydrated at 600 degrees C/2 kbar using hematite/magnetite-(HM), quartz/fayalite/magnetite- (QFM), wuestite/iron-(WI), quartz/fayalite/iron-(QFI) and Mn/MnO-buffers in order to determine the influence of different water activities (a (sub H2O) ) on the water content in cordierite. With decreasing a (sub H2O) only a slight decrease of water content in cordierite was observed, but its extent is smaller than the theoretically calculated decrease of a (sub H2O) m the fluid phase under these conditions. The equilibrium water contents of synthetic cordierites with F = 0.00, 0.25, 0.50, 0.75 and 1.00 (at WI buffer) were determined in the range of 500 degrees C-750 degrees C and 2-9 kbar. As in pure Mg-cordierite, the water content in Fe (super 2+) -bearing cordierite increases with increasing pressure and decreases slightly with increasing temperature. Within the error of measurement no systematic change of the water content in relation to F was found.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 2
Serial Issue: 5
Title: Synthesis and water contents of Fe (super 2+) -bearing cordierites
Affiliation: Ruhr-Univ. Bochum, Inst. Mineral., D-4630 Bochum 1, Federal Republic of Germany
Pages: 565-584
Published: 199010
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 60
Accession Number: 1995-050507
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 8 tables, 9 anals.
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany
Update Code: 199518
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