The redefinition of gunterite, Na4Ca[V10O28]·20H2O

Gunterite was originally assigned the ideal formula Na4[H2V10O28]·22H2O. More detailed bond-valence analysis brought into question the presence of a protonated decavanadate anion, which led to the reexamination of the mineral. Infrared spectroscopy confirmed the absence of NH4. Reinterpretation of the original crystal structure data and new electron-probe microanalyses support the redefinition of gunterite as having the ideal formula Na4Ca[V10O28]·20H2O. This redefinition has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association.