Haemozoin or hemozoin is formed by blood-feeding parasites as the end product of their digestion. It is usually formed by the digestion of blood. Parasites, after digesting hemoglobin, release large amounts of free-heme, and free-heme is toxic to cells.
So the parasites convert the free-heme into an insoluble, crystalline form called hemozoin. Hence, hemozoin appears to have a crystalline structure when observed under a microscope.
Haemozoin is important for the survival of parasites, hence present and emerging antibiotics inhibit the formation of hemozoin, thereby killing the parasites.