Vandall T. King

Epidote supergroup nomenclature: The names hancockite, niigataite and tweddillite reinstated

Abstract The epidote-group nomenclature report by Armbruster et al. (2006) provides a clear and concise definition of the epidote group, and a set of consistent rules and naming conventions for establishing new subgroups and mineral species within what is now the epidote supergroup (Mills et al., 2009). In order to comply with these rules, it was decided to rename the already approved minerals hancockite, niigataite and tweddillite to epidote-(Pb), clinozoisite-(Sr) and manganipiemontite-(Sr), respectively. These names were already well established within the mineral community, and the renaming caused some controversy. Recent International Mineralogical Association guidelines (Hatert et al. 2013) have given priority to the historical provenance of names over nomenclature consistency. Hatert et al. (2013) state as a main principle that “retroactivity will not be applied”, but that “Every change in nomenclature has to go through the CNMNC, and is examined on its own merit”, thus establishing a mechanism for re-instating historical names on a case by case basis. The CNMNC (Commission on New Minerals, Nomenclature and Classification Committee of the International Mineralogical Association) has therefore decided, as an exception to the main principle, to re-instate hancockite, niigataite and tweddillite. In part to maintain the historical names but, more importantly, re-establish the link between the mineral names and their structural and chemical definitions.