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

Halilsarpite, [Mg(H2O)6][CaAs23+(Fe2.673+Mo0.336+)(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