Magnetite particles containing a silicon component inside, and having the silicon component exposed on the surface in a proportion of {TAIL ~ 0.05 to 2.0%} by weight as {HEAD ~ 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 
Magnetite particles containing a silicon component inside , and having the silicon component exposed on the surface in a proportion of { TAIL ~ 0.05 to 2.0 % } by weight as { HEAD ~ 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
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD 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