Puttapaite, Pb₂Mn²⁺₂ZnCr³⁺₄O₂(AsO₄)₄(OH)₆·12H₂O, a new mineral from the Beltana deposit, Puttapa, Flinders Ranges, South Australia, Australi

Abstract Puttapaite, Pb 2 Mn 2+ 2 ZnCr 3+ 4 O 2 (AsO 4 ) 4 (OH) 6 ·12H 2 O, is a new mineral from the Beltana deposit, Puttapa, Flinders Ranges, South Australia, Australia. It forms rosette-like aggregates to 50 micrometers across composed of diamond-shaped tablets to 45 micrometers in length and 5 micrometers in thickness. Crystals are flattened on {001} and the observed forms are {001} and {110}. The calculated density is 3.562 g/cm –3 . Optically, puttapaite is biaxial (−) with α = 1.700(5), β = 1.720(5), γ = 1.730(5) and 2V (meas.) = 67(1)°. Electron microprobe analyses gave the empirical formula (based on 36 oxygen atoms pfu) Pb 1.96 (Mn 2+ 1.52 Ca 0.28 Sr 0.22 ) Σ2.02 (Zn 0.40 Mg 0.39 Cu 0.15 ) Σ0.94 (Cr 3+ 2.89 Al 0.45 Fe 3+ 0.40 ,Mn 3+ 0.26 ) Σ4.00 O 2 [(AsO 4 ) 3.71 (Cr 6+ O 4 ) 0.29 ] Σ4.00 (OH) 6.13 ·11.87H 2 O. Puttapaite is monoclinic, C 2/m, with a = 12.405(3), b = 10.565(2), c = 12.311(3) Å, β = 106.06(3)°, V = 1550.4(6) Å 3 and Z = 2. The structure was solved using synchrotron single-crystal X-ray diffraction data and refined to R 1 = 0.1189 on the basis of 915 observed reflections with F 0 > 4σ( F 0 ). Puttapaite has a unique structure that consists of M 4 O 16 clusters that share corners with T O 4 tetrahedra, which in turn share corners with M 1 octahedra in the [010] direction. Clusters link in the [001] direction via corner sharing M 2 octahedra to form sheets parallel to {100}. Pb anions lie between the sheets.