and when {HEAD ~ the amount} of presence of the silicon component exposed on {TAIL ~ the surface}, expressed in terms of silicon, with respect to the magnetite particles is designated as B, the relationship C/B≧15 is satisfied 
and when { HEAD ~ the amount } of presence of the silicon component exposed on { TAIL ~ the surface } , expressed in terms of silicon , with respect to the magnetite particles is designated as B , the relationship C / B≧15 is satisfied
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH 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