Cluster of neon yellow rhombs of Cadmium Smithsonite. Smithsonite, or zinc spar, is zinc carbonate (ZnCO3), a mineral ore of zinc. Smithsonite is a variably colored trigonal mineral which only rarely is found in well formed crystals. Smithsonite occurs as a secondary mineral in the weathering or oxidation zone of zinc-bearing ore deposits. It sometimes occurs as replacement bodies in carbonate rocks and as such may constitute zinc ore. Specimen from Tsumeb Mine, Tsumeb, Namibia, South Africa. Specimen Dimension: 2.5 x 2.5 cm.