Mineralogical characterization of the gem-variety pink clinozoisite from Val Malenco, Central Alps, Italy

Abstract

Val Malenco located in the Central Alps, Italy, is the source of a pink gem-variety clinozoisite better known in literature as “clinothulite” which stands for “monoclinic thulite”. “Thulite” is the obsolete name of the opaque pink Mn3+-bearing zoisite used as ornamental stone. In Val Malenco, the best-known occurrence of pink clinozoisite is the locality of Pizzo Tremogge, where the outcrop is enclosed in gneiss strictly associated with calcium silicate marbles of Paleozoic age. In this paper, we provide a characterization of this material by classical gemological methods, X-ray powder diffraction and microprobe chemical analyses. We also provide new data from another clinozoisite from the locality of Pra’ Isio (Valtellina) very close to Val Malenco. This clinozoisite has a similar pink hue, but shows a coarser grained texture that makes carving more difficult. The gemological properties, basic crystallographic data and chemical composition of the examined samples are consistent with those reported in literature for pink clinozoisite from other deposits of the world. The content of manganese is low (up to a maximum of 0.01 apfu), but still sufficient to give the mineral its characteristic and agreeable pink color.