What is the main useful compound found in haematite?

Haematite is primarily composed of iron(III) oxide, which is a key mineral source of iron. Iron(III) oxide, also known as ferric oxide, has the chemical formula Fe₂O₃ and is the most important ore of iron, widely used in the production of iron and steel.

When haematite is processed, it is reduced to produce iron, which is vital for many industrial applications, from construction to manufacturing. This makes iron(III) oxide not only the main useful compound found in haematite but also essential in understanding the extraction of metals from ores in the field of chemistry and materials science. The other options listed do not represent the primary compound found in haematite, as they pertain to different minerals or compounds unrelated to iron production.