Two series of strontium-lanthanum apatites, Sr10-xLax(PO4)(6-x)(SiO4)(x)F-2 and Sr10-xLax(PO4)(6-x)(SiO4)(x)O with 0 <= x <= 6, were synthesized by solid state reaction in the temperature range of 1200-1400 degrees C. The obtained materials were characterized by powder X-ray diffraction, infrared absorption spectroscopy and solid P-31 Nuclear Magnetic Resonance. Pure solid solutions were obtained within a limited range of unsubstituted phosphate and silicate apatites. A variation of the lattice parameters was observed, with an increase of a and a decrease of c parameters, related to the radius of the corresponding substituted ions. (c) 2006 Elsevier Ltd. All rights reserved.