Prossima pubblicazione.
Referenza:
▪ Yang, H., Gu, X., Jenkins, R.A., Gibbs, R.B., Downs, R.T. (2023): Bernardevansite, Al2(Se4+O3)3⋅6H2O, dimorphous with alfredopetrovite and the Al-analogue of mandarinoite, from the El Dragón mine, Potosí, Bolivia. Mineralogical Magazine, 87, (in press).
Abstract:
A new mineral species, bernardevansite (IMA 2022-057), ideally Al2(Se4+O3)3·6H2O, has been discovered from the El Dragón mine, Potosí Department, Bolivia. It occurs as aggregates or spheres of radiating bladed crystals on a matrix consisting of Co-bearing krut’aite–penroseite. Associated minerals are Co-bearing krutˊaite–penroseite, chalcomenite, and clinochalcomenite. Bernardevansite is colorless in transmitted light, transparent with white streak and vitreous luster. It is brittle and has a Mohs hardness of 2 3 Cleavage i not o erve . The measured and calculated densities are 2.93(5) and 2.997 g/cm3 , respectively. Optically, bernardevansite is biaxial (+), with α = 1.642(5), β = 1.686(5), γ = 1.74(1) (white light). An electron microprobe analysis yielded an empirical formula (based on 15 O apfu) (Al1.26Fe3+0.82)Σ2.08(Se0.98O3)36H2O, which can be simplified to (Al,Fe3+)2(SeO3)36H2O. Bernardevansite is the Al-analogue of mandarinoite, Fe3+2(SeO3)36H2O ordimorphous with P-62c alfredopetrovite. It is monoclinic, with space group P21/c and unit-cell parameters a = 16.5016(5), b = 7.7703(2), c = 9.8524(3) Å, β = 98.258(3) °, V = 1250.21(6) Å3, and Z = 4. The crystal structure of bernardevansite consists of a cornersharing framework of M3+O6 (M = Al, Fe) octahedra and Se4+O3 trigonal pyramids, leaving large voids occupied by the H2O groups. There are two unique M3+ positions: M1 is octahedrally coordinated by (4O + 2H2O) and M2 by (5O + H2O). The structure refinement indicates that Al preferentially occupies M1 (= 0.692Al + 0.308Fe) over M2 (= 0.516Al + 0.484Fe). The substitution of the majority of Fe in mandarinoite by Al results in a significant reduction in its unit-cell volume from 1313.4 Å3 to 1250.21(6) Å3 for bernardevansite. The discovery of bernardevansite begs the question whether the Fe3+-end-member, Fe3+2(SeO3)3·6H2O, has two polymorphs as well, one with P21/c symmetry, as for mandarinoite, and the other P-62c, as for alfredopetrovite.
NdR: Mandarinoite group
Alfredopetrovite Al2(Se4+O3)3·6H2O hex P62c 8.818 8.818 10.721 90.00 120.00 90.00 4
Bernardevansite Al2(Se4+O3)3∙6H2O mon P21/c 16.5016 7.7703 9.8524 90.00 98.258 90.00 4
Mandarinoite Fe3+2(Se4+O3)3·6H2O mon P21/c 16.81 7.88 10.02 90.00 98.3 90.00 4
Telluromandarinoite Fe3+2(Te4+O3)3·6H2O mon P21/c 16.9356 7.8955 10.1678 90.00 98.0064 90.00 4
Non è che, per qualche motivo, i dati relativi alla alfredopetrovite sono fasulli? O-D? Il lato a (parametro di cella) della alfredopetrovite è la metà degli altri lati a.
Potrebbe essere di interessamento per il Prof. Merlino. Ma, magari, invece è tutto OK. Stranezze naturali!
In effetti gli spettri Raman di alfredopetrovite e di bernardevansite non sono simili e porterebbero a dire che è tutto OK.
IMA 2022-057 = bernardevansite
- Marco E. Ciriotti
- Messaggi: 31675
- Iscritto il: ven 25 giu, 2004 11:31
- Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
- Contatta:
IMA 2022-057 = bernardevansite
Marco E. Ciriotti
«Things are interesting only in so far as they relate themselves to other things»
«Things are interesting only in so far as they relate themselves to other things»
- Marco E. Ciriotti
- Messaggi: 31675
- Iscritto il: ven 25 giu, 2004 11:31
- Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
- Contatta:
Re: IMA 2022-057 = bernardevansite
Pubblicazione effettuata.
Referenza:
▪ Yang, H., Gu, X., Jenkins, R.A., Gibbs, R.B., Downs, R.T. (2023): Bernardevansite, Al2(Se4+O3)3⋅6H2O, dimorphous with alfredopetrovite and the Al-analogue of mandarinoite, from the El Dragón mine, Potosí, Bolivia. Mineralogical Magazine, 87, 407-414.
Referenza:
▪ Yang, H., Gu, X., Jenkins, R.A., Gibbs, R.B., Downs, R.T. (2023): Bernardevansite, Al2(Se4+O3)3⋅6H2O, dimorphous with alfredopetrovite and the Al-analogue of mandarinoite, from the El Dragón mine, Potosí, Bolivia. Mineralogical Magazine, 87, 407-414.
Marco E. Ciriotti
«Things are interesting only in so far as they relate themselves to other things»
«Things are interesting only in so far as they relate themselves to other things»
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