"Monsmedite", a discredited potassium thallium sulphate mineral from Baia Sprie and its identity with voltaite: The state of the art

Abstract : "Monsmedite" was described half a century ago as a new potassium thallium sulphate mineral occurring in Baia Sprie, Romania. It was reported to occur as very dark green, morphologically cubic crystals with idealized formula Tl2O3.K2O.8SO3.15H2O. Many of the data published are close to those of usual voltaite, but the chemical composition and the measured density are clearly different. Up to now, all samples labelled "monsmedite" in mineral collections (including a co-type specimen of "monsmedite") proved to be usual voltaite with only very minor amounts of thallium. On this basis, and because the original "monsmedite" sample has gone lost, the Commission on New Minerals and Minerals Names of IMA decided to discredit "monsmedite" as a new mineral and to recommend that the name should be reserved for a possible find of a specimen that fulfills the description and chemical composition of "monsmedite".