Iron oxide blue is mainly composed of magnetite. The chemical composition of magnetite is Fe3O4. The crystal belongs to the oxide of equiaxed system. Iron blue has high coloring power, good light resistance, poor alkali resistance and high heat resistance. When the temperature exceeds 150 ℃, it loses crystal water and begins to decompose into red pigments. Application: paint making, ink, painting, pigment and crayon, paint cloth, paint paper, plastic products coloring, building floor, floor tile coloring, etc.