IMA 2020-073 = devilliersite

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Marco E. Ciriotti
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IMA 2020-073 = devilliersite

Messaggio da Marco E. Ciriotti » sab 25 set, 2021 13:33

Prime informazioni in:

Referenza:
▪ Krüger, B., Krüger, H., Galuskina, I. O., Galuskin E. L., Vapnik, Y. (2021): The crystal structure of the new mineral devilliersite Ca4Ca2Fe3+10O4[(Fe3+10Si2)O36]. Poster, MinPet 2021, Vienna, Austria, September 19-21, 2021; Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 167, 121.

Altro in: https://www.mindat.org/min-55320.html
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 31675
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: IMA 2020-073 = devilliersite

Messaggio da Marco E. Ciriotti » gio 24 feb, 2022 11:07

Il poster è stato pubblicato in:

Referenza:
▪ Krüger, B., Krüger, H., Galuskina, I. O., Galuskin E. L., Vapnik, Y. (2021): The crystal structure of the new mineral devilliersite Ca4Ca2Fe3+10O4[(Fe3+10Si2)O36]. Acta Crystallographica Section A: Foundations and Advances, A77, C1141-C1142.

Text:
The crystal structure of the new mineral (IMA 2020-073) devilliersite Ca4Ca2Fe3+10O4[(Fe3+10Si2)O36], crystalizing in space group P–1 with cell parameters a = 10.56619(10) Å, b = 10.94969(11) Å, c = 9.08459(7) Å, α = 106.4300(8)°, β = 95.7466(7)°, γ = 124.2978(11)°, V = 786.906(16) Å3, Z=1, was solved from single-crystal diffraction data, collected at PSI(SLS). Devilliersite, as well as khesinite, Ca4Mg2Fe3+10O4 [(Fe3+10Si2)O36], is a VIFe3+-analog of dorrite, Ca4Mg2Fe3+10O4[(Al10Si2)O36] and synthetic SFCA (Silico-Ferrite of Calcium and Aluminium). The structural formula of minerals of the dorrite–khesinite series can be written as VII(A12A22)Σ4VI(M1M2M32M42M52M62M72)Σ12O4[(T12T22T32T42T52T62)Σ12O36], where A are seven coordinated sites, M are octahedral sites and T are tetrahedral sites. The total scattering densities at the cation positions were determined using the atomic scattering factors combined with a refinement of the individual site occupancies and results of microprobe analysis.
In the structure of devilliersite all of the A-sites are fully occupied by calcium. However, chemical analyses show that additional 0.68 Ca atoms are present. For crystallochemical reasons this excess Ca has to be expected at the largest octahedral site M5, where it was placed and fixed for the refinement. The remaining scattering power at the M5 site is explained by Mg. The octahedral M1, M2, M3, M4 and M6 sites are dominated by Fe3+, their scattering power was modelled with Fe and Mg, and converged for all sites to ~93% Fe. The M7 octahedra shows the smallest level of distortion, with bond lengths ranging from 1.999(2) to 2.75(19). In the Ti-rich minerals of the rhönite-group, titanium is found at the M7 site. Therefore, we fixed Ti at this site, according to the results of the chemical analysis, and the remaining occupancy was refined as Fe vs. Mg. Scattering power indicates that the T4 site in devilliersite is fully occupied by Si. Occupancy of all other tetrahedral sites was refined as Al vs Fe. The refined chemical formula is VIICa4VI(Ca1.36Mg1.33Fe9.07Ti0.24)Σ12O4IV(Al3.24Fe6.76Si2)Σ12O36.
Marco E. Ciriotti

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