Zincostottite, ZnGe(OH)₆, the zinc analogue of stottite from Tsumeb, Namibia

Abstract The new mineral zincostottite (IMA2024-024), ZnGe(OH) 6 , was found on specimens from the Tsumeb mine, Tsumeb, Namibia, where it is a secondary oxidation-zone mineral. It occurs as heavily etched remnants of equant or tabular crystals, up to ∼1 mm in diameter. Crystals are colourless and transparent, with vitreous to subadamantine lustre and a white streak. The mineral is brittle with irregular stepped fracture. The Mohs hardness is ∼4.5. Cleavage is good on {100} and poor on {001}. The calculated density is 3.834 g·cm –3 . Optically, zincostottite is uniaxial (–) with ω = 1.785(5) and ε = 1.765(5) (white light). The empirical formula is (Zn 0.77 Fe 3+ 0.23 ) Σ1.00 Ge 1.00 O 6 H 5.77 . Zincostottite is tetragonal, space group P 4 2 / n , with cell parameters: a = 7.4522(18), c = 7.4000(8) Å, V = 411.0(2) Å 3 and Z = 4. The crystal structure ( R 1 = 2.65% for 452 I > 2σ I reflections) is the same as that of stottite with Zn in place of Fe 2+