{HEAD ~ Magnetite particles} containing {TAIL ~ 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 moisture resistance as indicated by moisture content of magnetite , measured under high temperature, high humidity conditions , and given by the equation 
{ HEAD ~ Magnetite particles } containing { TAIL ~ 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 moisture resistance as indicated by moisture content of magnetite , measured under high temperature , high humidity conditions , and given by the equation
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH