Al-doped La 9.33+x/3+y Si 6-x Al x O 26+3y/2 (x = 0-1.5, y = 0-0.67) apatite-type lanthanum silicates (ATLS) were synthesized with a high-power (1200 rpm) planetary ball mill that allows the formation of the lanthanum silicate phase after milling for 20-35 min at room temperature. The apatite phase already appears after milling for 5 min. Phase, structural and microstructural studies on the nanocrystalline lanthanum silicates were carried out by using XRD, TEM, and IR, 27 Al and 29 Si MAS NMR spectroscopy to clarify the mechanism of ATLS formation. The cluster-topotactic mechanism of the formation