The impact of mechanochemical treatment on a mixture of La2O3 and silica gel (in molar ratio La2O3/SiO2 = 1:2) was examined by X-ray powder diffractometry, infrared spectroscopy and thermal analysis. Unlike pure La2O3, complete amorphization of the mixture takes place after 3-h milling. A lanthanum orthosilicate is formed in an amorphous state as a precursor of La2Si2O7. Subsequent thermal treatment of the milled samples leads to the crystallization of pure A- or G-La2Si2O7, depending on the temperature.