During the roasting of pyrite ore, a mixture of FeO and Cu₂O is obtained.

2CuFeS₂ + O₂ + heat → Cu₂S + 2FeS + S₂

2Cu₂S + 3O₂ + heat → 2Cu₂S + 2SO₂

2FeS + 3O₂ + heat → 2FeO + 2SO₂

The role of silica in the metallurgy of copper is to remove the iron oxide obtained during the process of roasting as 'slag'. If the sulphide ore of copper contains iron, then silica (SiO₂) is added as flux before roasting. Then, FeO combines with silica to form iron silicate, FeSiO₃ (slag).

FeO + SiO₂ + heat → FeSiO₃ (Slag)