IMA 2019-023 = halilsarpite

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Marco E. Ciriotti
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IMA 2019-023 = halilsarpite

Messaggio da Marco E. Ciriotti » sab 01 feb, 2020 15:19

Referenza:
▪ Husdal, T., Grey, I.E., Friis, H., Dal Bo, F., Kampf, A.R., MacRae, C.M., Mumme, W.G., Ljøstad, O.T., Shanks, F. (2020): Halilsarpite, a new arsenate analogue of walentaite, from the Oumlil mine, Bou Azzer district, Morocco. European Journal of Mineralogy, 32, 89-98.

Abstract:
Halilsarpite, [Mg(H2O)6][CaAs3+2(Fe3+2.67Mo6+0.33)(AsO4)2O7], is a new secondary mixed arsenate/arsenite mineral from the Oumlil mine, Bou Azzer district, Morocco. It forms lemon-yellow spherules, about 0.1 mm in diameter, composed of platelets, some tens of micrometres in diameter but only 1–2 µm thick. The platelets are flattened on {100} and exhibit perfect cleavage on {100}. The calculated density is 2.89 g cm−3. Optically, halilsarpite is biaxial (−), with α=1.646(calc), β=1.765(5), γ=1.815(5) (white light), and 2V (meas.) = 62(1)∘. The partial orientation is X=a. Dispersion is weak with r<v, and pleochroism is in shades of yellow, X<Y≈Z. Electron microprobe analyses coupled with crystal-structure refinement results give the empirical formula [(Mg0.42Ca0.19Fe3+0.11 □0.28)Σ1.00 (H2O)6][((Ca0.5Mg0.2Na0.11□0.14)Σ0.95 (As3+)2.05)∑3.00(Fe3+2.44 Mo6+0.56)Σ3.00 ((As5+0.985P5+0.015)Σ1.00O4)2O6.9(OH)0.1]. Halilsarpite is orthorhombic, Imma, with a=26.4890(10), b=7.4205(3), c=10.4378(4) Å, V=2051.67(14) Å3, and Z=4. The structure was solved and refined using single-crystal X-ray data to wRobs=0.046 for 1402 unique reflections to a resolution of 0.75 Å. Halilsarpite is isostructural with walentaite and natrowalentaite, which have structures based on heteropolyhedral layers of configuration [M1(M2)2(TO4)2(O,OH)6] with surface-attached As3+O3 groups and Ca and Na cations, and with interlayer hydrated cations and H2O molecules. The octahedrally coordinated sites M1 and M2 are occupied by Fe3+ in walentaite, while M2 = Fe3+0.67W6+0.33 in natrowalentaite. Walentaite and natrowalentaite are phosphates, with T=P5+. Halilsarpite differs from these minerals in having T=As5+ and in having partial replacement of Fe3+ by Mo6+ in the M2-centred octahedra.

NdR: Vedasi anche: viewtopic.php?f=5&t=10790&p=257176&hili ... te#p257176
Marco E. Ciriotti

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