Abstract: The thickness of amorphous silicon dioxide on the surface of fine quartz was detected by TEM，SED and EDS methods and its volume and weight content computed.
Moreover, its effect on the hollow secondary particles of xonotlite produced by hydrothermal reactions was studied. Reaction products were investigated by XRD
and SEM methods. The experiment results show low content of amorphous silicon dioxide in the surface has no effect on the formation of the hollow secondary
particles of xonotlite, but high content delays their formation and leads to produce aggregates of xonotlite and tobermorite crystals.

Key words: quartz, amorphous silica, xonotlite