Nancyrossite, FeGeO ₆ H ₅ , a new hydroxyperovskite

Abstract Nancyrossite, ideally FeGeO 6 H 5 , is a new hydroxyperovskite from Tsumeb. It probably formed by the oxidation and partial dehydrogenation of stottite, FeGe(OH) 6 , with which it is associated intimately. The structure of nancyrossite has been determined in tetragonal space group P 4 2 / n: a = 7.37382(12) Å, c = 7.29704(19) Å, V = 396.764(16) Å 3 , Z = 4, R 1 (all) = 0.034, wR 2 (all) = 0.051 and GoF = 1.057. Empirical formulae of two crystals have almost end-member compositions, Fe 3+ 1.01 Zn 0.03 Ge 0.98 O 6 H 5 and Fe 3+ 1.01 Zn 0.04 Ge 0.98 O 6 H 5 . Structure determination indicates that 88% of the Fe is ferric. The chemical formula proposed here for nancyrossite recognises that although H atoms form OH groups, writing the formula as FeGeO(OH) 5 implies that one of the six oxygen atoms is very underbonded, with a bond-valence sum of only ∼1.2 valence units. As such, H in nancyrossite may have novel crystal chemistry. For example, the five H atoms may be distributed dynamically over the six O atoms, a phenomenon that would be averaged by X-ray diffraction, and so go undetected. Nancyrossite is the Ge-analogue of jeanbandyite. By analogy with nancyrossite, we propose revision of the ideal formula of jeanbandyite from FeSnO(OH) 5 (Welch and Kampf, 2017) to FeSnO 6 H 5 .