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