IMA 2019-072 = alcantarillaite and the walentaite group

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Marco E. Ciriotti
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IMA 2019-072 = alcantarillaite and the walentaite group

Messaggio da Marco E. Ciriotti » mer 18 mar, 2020 10:00

Prossima pubblicazione.

Referenza:
▪ Grey, I.E., Hochleitner, R., Rewitzer, C., Riboldi-Tunnicliffe, A., Kampf, A.R., MacRae, C.M., Mumme, W.G., Kaliwoda, M., Friis, H., Martin, C.U. (2020): The walentaite group and the description of a new member, alcantarillaite, from the Alcantarilla mine, Belalcazar, Cordoba, Andalusia, Spain. Mineralogical Magazine, 84, (in press).

Abstract:
The general structural formula for the walentaite group is
[((A1yA1’1-y), A2)(H2O)n][Bx(As2)2-x(As3)M1(M2)2(TO4)2(O,OH)7], based on heteropolyhedral layers of configuration [M1(M2)2(TO4)2(O,OH)6], with surface-coordinated species at the B, As2 and As3 sites, and with interlayer hydrated cation groups centred at the A sites. The group is divided into walentaite and halilsarpite subgroups based on T = P5+ and As5+, respectively. Alcantarillaite, (IMA2019-072), [Fe3+0.5□0.5(H2O)4][CaAs3+2(Fe3+2.5W6+0.5)(AsO4)2O7], is a new member of the walentaite group from the Alcantarilla wolframite mine, Belalcazar, Cordoba, Andalusia, Spain. It occurs most commonly as lemon-yellow fillings together with massive scorodite in fissures and cracks in quartz adjacent to löllingite. It is also found as tiny yellow rosettes lining vugs and as spheroids of ultrathin blades. It is associated with scorodite, pharmacosiderite, ferberite and schneiderhöhnite. Optically it is biaxial (–), with α = 1.703(calc), β = 1.800(5), γ = 1.850(5), 2V = 68(1)° (white light). Dispersion is r > v, moderate. The optical orientation is X = a, Y = c, Z = b. The calculated density is 3.06 g·cm-3. Electron microprobe analyses together with crystal structure refinement results gives the empirical formula [Fe3+0.52□0.48(H2O)4][(Ca0.44K0.11Na0.05Fe2+0.24□0.42)As3+1.83][Fe3+2.54Al0.03W6+0.43)
((As0.65P0.35)O4)2O5.86 (OH)1.14]. Alcantarillaite is orthorhombic, with an average-structure described in Imma, and with a = 24.038(8) Å, b = 7.444(3) Å, c = 10.387(3) Å, V = 1858.6(11) Å3 and Z = 4. The structure (wRobs = 0.078 for 651 reflections to a resolution of 0.91 Å) differs most significantly from other walentaite-group members in having an interlayer A2 site occupied. Square-pyramidal polyhedra centred at the A2 sites form edge-shared dimers, (Fe3+)2O4(H2O)4. The dimers share vertices with TO4 anions in the layers on either side to form 8-sided channels along [010] occupied by H2O molecules.

walentaite group
walentaite subgroup
walentaite: [Mn(H2O)6][□As3+3Fe3+3(PO4)2O7]
natrowalentaite: [Fe0.5Na0.5(H2O)6][NaAs3+2(Fe3+2.33W6+0.67)(PO4)2O7]
halilsarpite subgroup
halilsarpite: [Mg(H2O)6][CaAs3+2(Fe3+2.67Mo6+0.33)(AsO4)2O7]
alcantarillaite: [Fe3+0.5□0.5(H2O)4][CaAs3+2(Fe3+2.5W6+0.5)(AsO4)2O7]
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: 26570
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 2019-072 = alcantarillaite and the walentaite group

Messaggio da Marco E. Ciriotti » mer 18 mar, 2020 21:04

Alacantarillaite è stata identificata dal SIUK AMI su campioni del socio Georges Favreau provenienti dal Marocco.
Marco E. Ciriotti

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

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