Iron oxide blue is mainly composed of magnetite. The chemical composition of magnetite is Fe3O4. XH2O. The crystal belongs to equiaxed oxide mineral.

　　Because of its magnetism, Fe3O4 was also called Cishi, magnetite and Xuanshi in ancient China. The intact single crystal is octahedron or rhombic dodecahedron. When it is rhombic dodecahedron, there are always stripes parallel to the long diagonal direction of the crystal plane. The aggregate is dense block or granular. The color is iron black, streaks are black, semi metallic luster, opaque, no cleavage, Mohr 5.5-6, specific gravity 4.8-5.3. It has strong magnetism. It is the strongest in minerals and can be attracted by magnet permanently.

　　Dark blue or light blue powder, bright color, strong coloring power, slightly poor covering power. The powder is hard. Quality standard: coloring power 95 ~ 105%, oil absorption 15-30%, water 1.0%, residue (200 mesh sieve) ≤ 1.0%, water soluble 1.0%.

　　Iron oxide 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.

　　Uses: paint, ink, painting, pigment and crayon, paint cloth, paint paper, plastic products coloring, building floor, floor tile coloring.