IMA 2016-072 = alpeite

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Marco E. Ciriotti
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IMA 2016-072 = alpeite

Messaggio da Marco E. Ciriotti » lun 20 mar, 2017 10:18

Prossima pubblicazione.

Referenza:
▪ Kampf, A.R., Carbone, C., Belmonte, D., Nash, B.P., Chiappino, L., Castellaro, F. (2017): Alpeite, Ca4Mn3+2Al2(Mn3+Mg)(SiO4)2(Si3O10)(V5+O4)(OH)6, a new ardennite-group mineral from Italy. European Journal of Mineralogy, 29, (in press).
Marco E. Ciriotti

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

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TOSATO FABIO
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Re: IMA 2016-072 = alpeite

Messaggio da TOSATO FABIO » lun 20 mar, 2017 19:54

Complimentoni a tutti!
Tosato Fabio
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Marco E. Ciriotti
Messaggi: 23405
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 2016-072 = alpeite

Messaggio da Marco E. Ciriotti » gio 06 apr, 2017 10:05

Prossima pubblicazione.

Referenza:
▪ Kampf, A.R., Carbone, C., Belmonte, D., Nash, B.P., Chiappino, L., Castellaro, F. (2017): Alpeite, CaM4Mn3+2Al2(Mn3+Mg)(SiO4)2(Si3O10)(V5+O4)(OH)6, a new ardennite-group mineral from Italy. European Journal of Mineralogy, 29, (in press).

Abstract:
Alpeite (IMA2016-072), CaM4Mn3+2Al2(Mn3+Mg)(SiO4)2(Si3O10)(V5+O4)(OH)6, is a new member of the ardennite group from the Monte Alpe mine, Liguria, Italy. It crystallized from V- and Mn-rich hydrothermal fluids in an oxidizing environment. Alpeite occurs as intergrowths of plates, flattened on {1 0 0} and exhibiting the forms {1 0 0}, {0 0 1}, {0 1 2} and {1 0 2}. The mineral is brownish red and transparent with a vitreous to silky lustre and beige streak. Crystals are brittle with a curved and stepped fracture, and a perfect cleavage on {1 0 0} and good cleavages on {0 1 0 and {0 0 1}. The Mohs' hardness is 5½ to 6. The calculated density is 3.374 g cm-3. The mineral is inert in concentrated HCl at room temperature. Optically, alpeite crystals are biaxial (-), with α = 1.747(3), β = 1.785(3) and γ = 1.808(3) (white light); 2V = 73(2); dispersion r>v, strong; the optical orientation X = a, Y = b, Z = c. Pleochroism is Y>Z>X in shades of reddish brown. Electron microprobe analyses gave the empirical formula (Ca3.84Mn2+0.16)Σ4.00(Mn3+1.33Al0.67)Σ2.00(Al1.29Mn3+0.60V5+0.10)Σ1.99(Mn3+0.70Mg0.65Al0.42Co2+0.20)Σ1.97(SiO4)2(Si3O10)[(V5+0.75Si0.25)O4](OH)6, based on 28O atoms per formula unit. Alpeite is orthorhombic, Pnmm, with the unit-cell parameters: a = 8.9421(11), b = 6.0534 (6), c = 18.9781(18)Å, V = 1027.29(19)Å3 and Z = 2. The four strongest lines in the X-ray powder diffraction pattern are [dobs/Å (I) (hkl)]: 3.022 (93) (1 1 5), 2.673 (100) (1 1 6), 2.572 (69) (2 0 6) and 1.5112 (83) (0 4 0,4 2 7). The crystal structure was refined to R1=0.044 for 834 observed reflections [Fo>>4σF]. The structure is the same as that of other members of the ardennite group. It contains chains of edge-sharing Mn3+ and Al octahedra extending along the b axis, which are linked into a framework by sharing corners with SiO4 tetrahedra and with Si3O10 tetrahedral groups. Within the cavities in this framework are 7-coordinated Ca sites. In the structure of alpeite, Mn3+ is the dominant cation in the M1 site and is the dominant trivalent cation in the M3 site, while in all other members of the ardennite group [ardennite-(As), ardennite-(V) and kannanite], Al is the dominant cation in the M1 site and is the dominant trivalent cation in the M3 site.
Marco E. Ciriotti

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