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.