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History of ardennite and the new mineral ardennite-(V)

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Ardennite-(V), ideally Mn4[Al4(AlMg)][Si5V]O22(OH)6, is the analogue of ardennite, ideally Mn4[Al4(AlMg)][Si5As]O22(OH)6, with V dominant at the T4 site. The history of the discovery of ardennite is outlined, with special accent on its chemical composition; revision of the old literature evidenced that even if vanadium-containing specimens were considered since the first description, the analytical data contained in the first papers are very questionable, and ardennite has been so far considered an arsenate-silicate. A new occurrence of ardennite-(V) is described from Sparone, Locana Valley (TO), Piedmont, Italy. Here ardennite-(V) occurs within a piemontite-bearing micaschist. Crystals are elongated along [010] and very thin (up to 1 mm in length and a few microns in diameter), are yellow with a white streak, transparent with a vitreous lustre, and brittle. No cleavage or parting were observed. The calculated density is 3.55 g/cm3. Optically, ardennite-(V) is biaxial, with α > 1.765(5), β < 1.775(5), and γ = 1.775(5), and is weakly pleochroic, with X, Y = pale yellow; Z = yellowish. Electron microprobe analyses (P2O5 0.38 wt.%, As2O5 0.37, V2O5 4.60, SiO2 31.21, TiO2 0.21, Al2O3 22.60, Fe2O3 1.64, Cr2O3 0.34, MgO 4.44, MnO tot 23.28, CaO 4.24, Na2O 0.02, F 0.17, H2O calc 5.70), gave the following empirical formula: [Mn2+ 3.221Ca0.774Na0.006]Σ = 4.001 [Al4.456Mg1.127Fe3+ 0.210Mn3+ 0.137Cr0.046Ti0.027]Σ = 6.003 [Si5.000] [V0.518Si0.315Al0.080P0.055As0.033]Σ =1.001 O21.433 (OH)6.475 F0.092. The five strongest peaks in the X-ray powder diffraction pattern [d(Å)(I)(hkl)] are: 2.948(90)(115), 2.609(100)(310/116), 2.033(55)(225), 1.585(75)(425), 1.477(45)(2.2.10). Ardennite-(V) is orthorhombic, space group Pnmm, with a 8.760(3), b 5.838(2), c 18.56(2) Å. Both the new mineral and its name were approved by the IMA CNMNC. Chemical analyses which point to the occurrence of ardennite-(V) were recorded also at Varenche mine, S. Barthelemy, Aosta Valley, Italy, but the crystal showed a marked zoning.
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Document Type: Research Article

Publication date: 2007-08-01

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  • The European Journal of Mineralogy publishes original papers, review articles and letters dealing with the mineralogical sciences s.l. These include primarily mineralogy, petrology, geochemistry, crystallography and ore deposits, as well as environmental, applied and technical mineralogy. Nevertheless, papers in any related field, including cultural heritage, will be considered.
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