7 1 45 0042 y 2 si 2 o 7 2 21 1459 fe 2 sio 4 1 71 1667 fe 2 sio 4 2 72 0297 y 2 sio 5 21 1461 u2014 fe 2 o 3 80 2377 u2014 fe 2 o 3 16 0653 y 2 o 3 44 0399 the calcined composites were ground in an agate mortar to reduce the grain size from about 50 u03bcm to submicron size the milled powder was mostly pure silica without yig particles because the yig particles in the original cpg grains were concentrated primarily in a 0 5 u03bcm subsurface layer significant color changes were observed after removing this subsurface layer for example sample b 4 was tinged with deep red color due to the presence of u2014 fe 2 o 3 which was formed by the decomposition of yig particles during calcination after grinding the color changed to white pink because of white cristobalite in the core of cpg grains revealed by the grinding the ground powder was put in a vial filled with 97 ethanol and stirred strongly before all the fragments deposited in the bottom of the vial the supernatant liquid was removed so that excess pure silica fragments were removed the specific gravity of cpg fragments which contained yig nanocrystals was greater than.