Magnetite particles containing a silicon component inside, and having the silicon component exposed on the surface in a proportion of 0.05 to 2.0% by weight as silicon which have improved {HEAD ~ moisture resistance} as indicated by {TAIL ~ moisture content} of magnetite , measured under high temperature, high humidity conditions , and given by the equation 
Magnetite particles containing a silicon component inside , and having the silicon component exposed on the surface in a proportion of 0.05 to 2.0 % by weight as silicon which have improved { HEAD ~ moisture resistance } as indicated by { TAIL ~ moisture content } of magnetite , measured under high temperature , high humidity conditions , and given by the equation
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH