smithsonite

Sharp rhombs of colourless to mustard-yellow smithsonite (individually to 11 mm), intergrown to form a three-dimensional druse on dark-grey to black massive sulphide. The smithsonite crystals carry minute inclusions of yellow-brown iron oxides (confirmed by wet chemistry), possibly goethite (?). Under magnification the distribution of these inclusions is seen to be zoned, defining growth phantoms in many of the crystals (Exhibit 2).

The specimen was purchased from British dealer Nick Carruth in 1999 but with no record of its earlier provenance.

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 2023; Southwood et al. 2025); analytical data is presented in Exhibit 3. The visible inclusions of iron oxides undoubtedly contribute to the colour of the specimens, but colour formation is probably supplemented by the partial oxidation of Fe (15568 ppm) in solid solution in the smithsonite. A moderate amount of Cd (3094 ppm) is present, but the low S tenor (115 ppm) implies that the overwhelming majority of the Cd is in solid solution in the carbonate.

goethite