text: In the case of sulfides and carbonates, a process called "roasting" removes the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A few practical examples:
  * Malachite, a common ore of copper is primarily copper carbonate hydroxide Cu(CO)(OH). This mineral undergoes thermal decomposition to 2CuO, CO, and HO in several stages between 250 °C and 350 °C. The carbon dioxide and water are expelled into the atmosphere, leaving copper(II) oxide, which can be directly reduced to copper as described in the following section titled Reduction.
  * Galena, the most common mineral of lead, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfite (PbSO), which thermally decomposes into lead oxide and sulfur dioxide gas (PbO and SO). The sulfur dioxide is expelled (like the carbon dioxide in the previous example), and the lead oxide is reduced as below.