Thermal analysis of smithsonite and hydrozincite

Thermogravimetric analysis of synthetic smithsonite and hydrozincite, two secondary minerals of zinc, was used to determine their relative thermal stability. Thermal decomposition of smithsonite occurs at 293°C and hydrozincite at 220°C showing that the carbonate mineral is more stable than the hydroxy-carbonate mineral hydrozincite. Hot stage Raman spectroscopy confirms the decomposition of smithsonite and hydrozincite by 300 and 250°C, respectively. Thermogravimetry shows that a small amount of hydrozincite is formed during the synthesis of smithsonite. No evidence is found for the separate loss of the carbonate and hydroxyl units from hydrozincite.