NOVELTY - An olivine type silicate compound has lithium iron silicate compound where peak intensity of (311) plane of magnetite with respect to the peak intensity of (002) plane of lithium iron silicate is less than or equal to 0.01 times, in the X-ray diffraction pattern.    USE - Olivine type silicate compound for lithium ion battery as lithium ion battery positive electrode (all claimed) used in mobile telephone, digital camera, notebook personal computer, hybrid vehicle and electric vehicle.    ADVANTAGE - Lithium ion battery using olivine type silicate compound has outstanding discharge capacity.    DETAILED DESCRIPTION - An olivine type silicate compound has lithium iron silicate compound of formula Li2FeSiO4 where peak intensity of (311) plane of magnetite (Fe3O4) with respect to the peak intensity of (002) plane of Li2FeSiO4 is less than or equal to 0.01 times, in the X-ray diffraction pattern. INDEPENDENT CLAIMS are included for:    (1) lithium ion battery positive electrode active material comprising olivine type silicate compound;    (2) lithium ion battery comprising positive electrode consisting of lithium ion battery positive electrode active material;    (3) manufacturing method of olivine type silicate compound which involves hydrothermal reaction of basic aqueous dispersion which contains lithium compound, silicic acid compound, and antioxidant performed using organic acid iron such as iron sulfate (FeSO4) or R2Fe; and    (4) manufacturing method of lithium ion battery positive electrode active which involves hydrothermal reaction of the basic aqueous dispersion which contains lithium compound, silicic-acid compound, and antioxidant, using organic acid iron FeSO4 or R2Fe, supporting carbon on obtained olivine type silicate compound, and baking.    R=organic acid residue.    DESCRIPTION OF DRAWING(S) - The drawing shows a graph of the X-ray diffraction pattern of freeze-dried olivine silicate compound powder. (Drawing includes non-English language text).