Halilsarpite, a new arsenate analogue of walentaite, from the Oumlil mine, Bou Azzer district, Morocco

Husdal, Tomas; Grey, Ian E.; Friis, Henrik; Dal Bo, Fabrice; Kampf, Anthony R.; MacRae, Colin M.; Mumme, W. Gus; Ljøstad, Ole-Thorstein; Shanks, Finlay

Halilsarpite, [Mg(inline-formulaH2O)inline-formula6][inline-formula M3inlinescrollmathml chem normal CaAs normal 2 normal 3 + 39pt17ptsvg-formulamathimgfa7a53a4e8647f8fb2f5a9edb9f7bd2e ejm-32-89-2020-ie00001.svg39pt17ptejm-32-89-2020-ie00001.png (inline-formula M4inlinescrollmathml chem normal Fe normal 2.67 normal 3 + 30pt17ptsvg-formulamathimgb46dc947db56806847d6fd746f204dd0 ejm-32-89-2020-ie00002.svg30pt17ptejm-32-89-2020-ie00002.png inline-formula M5inlinescrollmathml chem normal Mo normal 0.33 normal 6 + 33pt17ptsvg-formulamathimg58f3ab357d9c291f95b60f89be6be14e ejm-32-89-2020-ie00003.svg33pt17ptejm-32-89-2020-ie00003.png )(inline-formulaAsO4)inline-formula2inline-formulaO7], 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 inline-formulaµm thick. The platelets are flattened on inline-formula{100} and exhibit perfect cleavage on inline-formula{100}. The calculated density is 2.89 g cminline-formula−3. Optically, halilsarpite is biaxial (inline-formula−), with inline-formulaα=1.646(calc), inline-formulaβ=1.765(5), inline-formulaγ=1.815(5) (white light), and 2V (meas.) inline-formula= 62(1)inline-formula. The partial orientation is inline-formulaX=a. Dispersion is weak with inline-formular<v, and pleochroism is in shades of yellow, inline-formula M21inlinescrollmathml X < Y Z 51pt10ptsvg-formulamathimgdf98348652a9bc4854182b67c45b34b1 ejm-32-89-2020-ie00004.svg51pt10ptejm-32-89-2020-ie00004.png . Electron microprobe analyses coupled with crystal-structure refinement results give the empirical formula inline-formula M22inlinescrollmathml [ ( chem normal Mg normal 0.42 chem normal Ca normal 0.19 chem normal Fe normal 0.11 normal 3 + 98pt17ptsvg-formulamathimgac8b04ef196e15d29c574990a8cb6c1d ejm-32-89-2020-ie00005.svg98pt17ptejm-32-89-2020-ie00005.png inline-formula0.28)Σ1.00inline-formula(H2O)6][((Ca0.5Mg0.2Na0.110.14)Σ0.95inline-formula M25inlinescrollmathml ( chem normal As normal 3 + ) normal 2.05 ) normal 3.00 ( chem normal Fe normal 2.44 normal 3 + 108pt18ptsvg-formulamathimg8d83ab19e9100cd59ca98c2aecef5a0c ejm-32-89-2020-ie00006.svg108pt18ptejm-32-89-2020-ie00006.png inline-formula M26inlinescrollmathml chem normal Mo normal 0.56 normal 6 + ) normal Σ normal 3.00 58pt17ptsvg-formulamathimg2899f0f49fc15c570f72ea7e15bcc3f0 ejm-32-89-2020-ie00007.svg58pt17ptejm-32-89-2020-ie00007.png inline-formula M27inlinescrollmathml ( ( chem normal As normal 0.985 normal 5 + chem normal P normal 0.015 normal 5 + ) normal Σ normal 1.00 chem normal O normal 4 ) normal 2 chem normal O normal 6.9 ( chem normal OH ) normal 0.1 ] 175pt17ptsvg-formulamathimg4c7cf81417492a3406856cf8f71c3212 ejm-32-89-2020-ie00008.svg175pt17ptejm-32-89-2020-ie00008.png . Halilsarpite is orthorhombic, Imma, with inline-formulaa=26.4890(10), inline-formulab=7.4205(3), inline-formulac=10.4378(4) Å, inline-formulaV=2051.67(14) Åinline-formula3, and inline-formulaZ=4. The structure was solved and refined using single-crystal X-ray data to inline-formulawRobs=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 [inline-formulaM1(M2)2(inline-formulaTinline-formulaO4)inline-formula2(O,OH)inline-formula6] with surface-attached inline-formulaAs3+inline-formulaO3 groups and inline-formulaCa and inline-formulaNa cations, and with interlayer hydrated cations and inline-formulaH2O molecules. The octahedrally coordinated sites inline-formulaM1 and inline-formulaM2 are occupied by inline-formulaFe3+ in walentaite, while inline-formulaM2 =inline-formula M49inlinescrollmathml chem normal Fe normal 0.67 normal 3 + 30pt17ptsvg-formulamathimgbf66f2bce39194a30ac0e2b60f8eff65 ejm-32-89-2020-ie00009.svg30pt17ptejm-32-89-2020-ie00009.png inline-formula M50inlinescrollmathml chem normal W normal 0.33 normal 6 + 28pt17ptsvg-formulamathimg90c9357d5ebcc468559246da33d0084c ejm-32-89-2020-ie00010.svg28pt17ptejm-32-89-2020-ie00010.png in natrowalentaite. Walentaite and natrowalentaite are phosphates, with inline-formula M51inlinescrollmathml T = chem normal P normal 5 + 39pt13ptsvg-formulamathimgf0c4b22c39cbcd2e43d3545676bfe067 ejm-32-89-2020-ie00011.svg39pt13ptejm-32-89-2020-ie00011.png . Halilsarpite differs from these minerals in having inline-formula M52inlinescrollmathml T = chem normal As normal 5 + 44pt13ptsvg-formulamathimg91f97254b6be736e44cebf689a46727c ejm-32-89-2020-ie00012.svg44pt13ptejm-32-89-2020-ie00012.png and in having partial replacement of inline-formulaFe3+ by inline-formulaMo6+ in the inline-formulaM2-centred octahedra.

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Husdal, Tomas / Grey, Ian E. / Friis, Henrik / et al: Halilsarpite, a new arsenate analogue of walentaite, from the Oumlil mine, Bou Azzer district, Morocco. 2020. Copernicus Publications.

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