IMA 2018-032a = natrowalentaite

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Marco E. Ciriotti
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IMA 2018-032a = natrowalentaite

Messaggio da Marco E. Ciriotti » gio 30 giu, 2022 11:46

Referenza:
▪ Grey, I.E., Mumme, W.G., Kampf, A.R., MacRae, C.M., Wilson, N.C. (2019): Natrowalentaite, a new mineral from the Griffins Find gold deposit, Western Australia. Australian Journal of Mineralogy, 20, 7-15.

Abstract:
Natrowalentaite, [Fe2+0.5Na0.5(H2O)6][NaAs3+2(Fe3+2.33W6+0.67)(PO4)2O7, is a new secondary phosphate mineral from the Griffins Find gold deposit, Western Australia. It forms aggregates of extremely thin (I to 3 µm), bright greenish-yellow blades with lengths up to 200 µm, on natropharmacosiderite. The blades are flattened on { JOO}, elongated on [0 JO] and ellhibit the forms { I 00}, { 00 I ) and { 0 I I ) . Cleavage is perfect on { I 00 }. The measured density is 2.91(2) g cm·3. Optically, natrowalentaite is biaxial (-), with a= 1.650(3), ~ = 1.728(3), y = 1.772(3) (white light), and 2V (meas.) = 71 (2) 0 • The orientation is X = a, Y = c, Z = b. Dispersion is distinct with r > v, and pleochroism is imperceptible. Electron microprobe analyses give the empirical formula Na1.09K0.07Ca0.30Fe3+2.57W6+0.70As3+2.10P2O21H12.02 based on 21 anions per formula unit. Natrowalentaite is orthorhombic, Imma, with a = 25.770(3), b = 7.3250(8), c = 10.522(1) A, V = 1986.2(4) A.3 and Z = 4. The structure was solved and refined using single-crystal synchrotron X-ray data to R1 = 0.062 for 875 unique reflections to a resolution of 0.7 A. atrowalentaite is isostructural with walentaite, which has a structure based on layers of composition (Fe,W)3(PO4)2(O,OH)6, with surface-attached As3•O3 groups and a/Ca cations and with interlayer hydrated cations and H,O. Natrowalentaite differs from walentaite in having dominant Na as a surface-attached cation, rather than Ca, and in having partial replacement of Fe3• by W6+ in the layers. The natrowalentaite and walentaite structures are unusual in that they contain (Asp6)3· trimeric clusters of pyramidal As3•O3 arsenite groups.

Ndr: walentaite group (alunite supergroup)
Aldermanite [Mg(H2O)6][Na(H2O)2Al3(PO4)2(OH)6]·H2O mon P21/c 13.524 9.958 7.013 90.00 97.40 90.00 2 936.6
Natrowalentaite [Fe2+0.5Na0.5(H2O)6][NaAs3+2(Fe3+2.33W6+0.67)(PO4)2O7] orth Imma 25.770 7.325 10.522 90.00 90.00 90.00 4 1986.188
Penriceite [Mg(H2O)6][Na(H2O)2Al3(PO4)2F6]⋅H2O mon P21/c 13.478 9.971 6.999 90.00 97.20 90.00 2 933.173
Walentaite [Mn2+(H2O)6][□As3+3Fe3+3(PO4)2O7] orth Imma 26.188 7.360 10.367 90.00 90.00 90.00 4 1998.174
Marco E. Ciriotti

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