smithsonite

A massive sulphide matrix comprising mainly galena and sphalerite (the latter showing a typical bright orange fluorescence under LW ultraviolet), hosts slender, elongated crystals (to 12 mm) of yellow-brown smithsonite. The smithsonite comprises two forms - a prism and a terminating rhombohedron - with tiny second generation crystals growing out of the faces of the larger crystals. A little quartz is associated.

The specimen was acquired from Ian Bruce in 2018 but there is no record of earlier provenance or location in the mine. The specimen has been analysed by EMPA-WDS and LA-ICP-MS as part of a study of the causes of colour in smithsonite (Weall 2022; Southwood et al. 2025). They hypothesised that the brown colouration is due to partial oxidation of ferrous iron solid solution in the smithsonite.  Analytical data is presented in Exhibit 2.

galena; quartz; sphalerite