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The behaviour of Mn in amphiboles; Mn in richterite

Roberta Oberti, Frank C. Hawthorne, Luciano Ungaretti and Elio Cannillo
The behaviour of Mn in amphiboles; Mn in richterite
European Journal of Mineralogy (February 1993) 5 (1): 43-51


The crystal structures and site occupancies of five manganoan richterites (MnO approx 20%) have been refined to R values of <= 2% using single-crystal MoK (sub alpha) XRD data. EPMA results indicate significant occupancy of the M(4) site by (Mn (super 2+) , Fe (super 2+) , Mg). Difference-Fourier maps show the presence of electron density within the M(4) cavity but displaced along the 2- fold axis towards the octahedral strip; this position is designated M(4'). Comparison between the results of the EPMA and the structure refinements of the same richterite crystals indicate that the M(4') site is dominantly occupied by Mn (super 2+) . At the octrahedrally-coordinated M(1,2,3) sites, Mn is present as Mn (super 2+) and is strongly ordered at the M(2) site. The M(1)-O and M(3)- O distances in richterites are linear functions of the amount of F (super -) right and left arrow OH (super -) substitution at the O(3) site. The need for dimensional matching among the three independent octahedral sites suggests that extensive F (super -) substitution is inhibited in manganoan richterites, in which the M(2) site is particularly large.

ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 5
Serial Issue: 1
Title: The behaviour of Mn in amphiboles; Mn in richterite
Affiliation: CNR, Centro di Studio per la Cristallochimica e la Cristallografia, Pavia, Italy
Pages: 43-51
Published: 199302
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 25
Accession Number: 1993-003534
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 1993
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