smithsonite (w. greenockite)

Brown, almost smoky, crystals of smithsonite (to 6 mm) comprising prism and rhombohedron forms, on massive sulphide, mainly galena, with a little quartz. The smithsonite has a dull lustre and appears to be lightly etched. The sulphide matrix between the smithsonite crystals has a cavernous texture and is also quite heavily etched; one area of this matrix is quite richly scattered with microscopic orange-brown crystals of greenockite (c. 0.2 mm).

The specimen was purchased from Ian Bruce in 2015, but its earlier provenance and location in the mine are not recorded.

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 Fe²⁺ in solid solution in the smithsonite. Analytical data is presented in Exhibit 2.

galena; greenockite; quartz