Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Letter to Editor

Jan Cempírek, Lee A. Groat

Note on the formula of brunogeierite and the first bond-valence parameters for Ge²⁺

Journal of Geosciences, volume 58 (2013), issue 1, 71 - 74

DOI: http://doi.org/10.3190/jgeosci.130

Brunogeierite is a rare Ge-mineral with a spinel-type structure. Inconsistences in the brunogeierite formula suggesting divalent germanium in its structure have occurred since its description. A review of the published data and bond-valence calculations show that the correct ideal end-member formula of brunogeierite is (Fe²⁺)₂Ge⁴⁺O₄. The mineral is newly classified as a nesogermanate member of the ringwoodite group (Strunz classification 9.AC.15). Formal correction of the brunogeierite formula and classification was approved by the IMA Commission on New Minerals, Nomenclature and Classification (IMA-CNMNC) as proposal IMA 11-A. To perform bond-valence calculations using divalent germanium, new bond-valence parameters for Ge²⁺-O (R₀ = 1.778 Å, B = 0.37 Å) and Ge²⁺-Cl (R₀ = 2.156 Å, B = 0.37 Å) were evaluated.