Crystal chemistry of julgoldite, a mineral series of the pumpellyite group: Re-investigation of Fe distribution and hydrogen-bonding

Nagashima, Mariko; Cametti, Georgia; Armbruster, Thomas Michael (2018). Crystal chemistry of julgoldite, a mineral series of the pumpellyite group: Re-investigation of Fe distribution and hydrogen-bonding. European journal of mineralogy, 30(4), pp. 721-731. E. Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller) 10.1127/ejm/2018/0030-2747

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Single-crystal X-ray crystal-structure refinements and electron-microprobe analyses of two julgoldite samples, in one case complemented by Mössbauer spectroscopy to determine the Fe valence distribution, yielded the compositions Ca2.00X(Fe2+0.44Fe3+0.29Mg0.17Al0.10)Y(Fe3+0.82Al0.18)2Si3O10.39(OH)3.61 (Bombay) and Ca2.00X(Fe0.67Mg0.16Al0.17)Y(Fe3+0.81Al0.19)2Si3O14-n(OH)n (4 ≥ n ≥ 3) (Kreimbach/Kaulbach), respectively. Structure refinements also allowed specification of the system of hydrogen bonds, which concur with those known for pumpellyite. A review of structural and chemical data for pumpellyite-group minerals including six julgoldite samples indicated that the length of the b axis is governed by the average size of ionic radii at the Y site, except for one sample of julgoldite-(Fe3+). Size effects of the concentration of “large” divalent cations (Mg, Fe) at the X site can be seen in the lateral extension of the (010) plane that acts as a buffer to accomplish the variable size of the X octahedra. Using unit-cell plots, the data suggest that five of the six tested julgoldite sample are julgoldite-(Fe2+) and only the one sample of the Bombay area studied by Artioli et al. (2003) is julgoldite-(Fe3+). Both samples studied in this paper were classified into julgoldite-(Fe2+). In contrast to pumpellyite samples sensu stricto, which exhibit a Me2+:Me3+ ratio of approximately 1:1, julgoldite samples may cover the whole range between Ca2X(Fe3+)Y(Fe3+)2Si3O11(OH)3 and Ca2X(Fe2+)Y(Fe3+)2Si3O10(OH)4.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Mineralogical Crystallography (discontinued)
08 Faculty of Science > Institute of Geological Sciences > Mineralogy

UniBE Contributor:

Cametti, Georgia and Armbruster, Thomas Michael

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0935-1221

Publisher:

E. Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller)

Language:

English

Submitter:

Georgia Cametti

Date Deposited:

14 Jun 2018 14:06

Last Modified:

31 Oct 2018 01:30

Publisher DOI:

10.1127/ejm/2018/0030-2747

BORIS DOI:

10.7892/boris.113064

URI:

https://boris.unibe.ch/id/eprint/113064

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