The main impurity in haematite is typically SiO3, also known as silica. Haematite is an iron ore consisting primarily of iron oxide (Fe2O3) and is a common source of iron. However, impurities can be present in the ore, and silica is one of the most common impurities. Silica can affect the quality of the iron produced from the ore and can cause problems during the smelting process. Therefore, it is important to remove as much silica as possible during the processing of haematite.