DISCREDITATION OF THOROGUMMITE

Thorogummite has been discredited as a valid mineral species. No type material from the original study was available for analysis. An extensive review of the literature, both recent and historic, reveals the use of the name “thorogummite” for any hydrated, metamict thorite or unidentified alteration product of a Th-bearing mineral. All early studies on “thorogummite” and other alteration products of thorite were performed on heterogeneous mixtures of mostly secondary and metamict materials and must be considered suspect. The validity of Frondel’s (1953) proposed (SiO 4 ) 4– ↔ (OH) 4 4– substitution between thorite and thorogummite was examined and shown to be an incomplete solid solution. All compositions in the literature to date are Th- and Si-dominant and must be considered thorite. Furthermore, the majority of the compositions in the literature are outdated and likely do not represent those from crystalline, single-phases. More likely, all so-called “thorogummite” are simply metastable hydrated or metamict thorite with varying volumes of other alteration products. The discreditation has been approved by the IMA Commission on New Minerals, Nomenclature and Classification (Nomenclature Voting proposal 14-B).