Namuwite, (Zn,Cu)₄SO₄(OH)₆.4H₂O, a new mineral from Wales

Found on a specimen in the mineral collection of the National Museum of Wales, no. NMW 27.111.GR414, from the Aberllyn mine, Llanrwst mining field, North Wales, with hydrozincite on a breccia cemented by sphalerite, quartz, calcite, and ankerite. Atomic absorption and TGA analyses gave ZnO 37.8, CuO 22.0, SO 3 14.9, H 2 O 24.5, total 99.2%, corresponding to (Zn 2.50 Cu 1.49 ) Σ3.99 S 1.00 O 7 ·7.32 H 2 O on the basis of total O = 7 in the anhydrous part. The ideal formula is (Zn,Cu) 4 SO 4 (OH) 6 ·4H 2 O where Zn > Cu. It is hexagonal a 8.29, c 10.50 ± 0.01 Å, possible space groups P 6, P , P 6/ m , P 622, P 6 mm , P m 2, P 2 m , and P 6/ mmm . Isomorphous with synthetic Zn,SO 4 (OH) 6 6·4H 2 O and (Zn,Cu) 4 SO 4 (OH) 6 ·4H 2 O. Strongest X-ray powder diffractions are: 10.59(100)0001, 5.31(15)0002, 4.15(25)11 0, 2.71(42)21 0, 2.63(41)21 1,0004, 2.41(22)21 2, 1.57(23)32 2, 1.55(20)41 1. Namuwite is pale sea-green in colour, lustre pearly, streak very pale green, H (Mohs) 2. Cleavage {0001}, perfect. Density (g/cm 3 ) 2.77 (meas.), 2.81 (calc. on the normalized empirical formula). It is optically uniaxial, sign not determined owing to the extremely low birefringence. Refractive index n = 1.577(5)(Na D ). The mineral and name have been approved by the Commission on New Minerals and Mineral Names, IMA.