Summary: Bandy (1938) described as metavoltine? a mineral coming from Chuquicamata (Chile) with chemical composition K2Na6Fe3+(SO4)12(OH)2·20H2O. Owing to some differences between this mineral and that first described by Blaas (1883), doubts persist on the identity of these two compounds. X-ray analyses were performed to clarify the relation between them. An artificial product, closely related to metavoltine as regards lattice and chemical composition, was also studied, and affords a better understanding of the Na and K diadochy already observed in metavoltine.