The effect of dry grinding of kaolin minerMs by a mechanical mortar was examined by
x-ray, thermal, and electron microscopic methods. Base exchange capacity and apparent
density were also measured. In the early stage of grinding, kaolin crystals cleave and
fracture and then split into fine crystals which are considered unit erystallites. Such
erystallites gradually change to a disordered kaolin and partially decompose into a
noncrystalline substance as grinding progresses. The crystalline and the noncrystalline
substances promptly reaggrogate and these reaggregated particles have a radial shape.
After further grinding, the structure of the reaggregated particle seems to be zeolitic.
Finally, the kaolin mineral thoroughly changes to a completely amorphous substance
similar to a silica-alumina mixed gel. Consequently, the effect of dry grinding of kaolin
is related to the degree of crystallinity of the original kaolin mineral.