Nanocrystals of BaF 2 precipitate during controlled annealing of silicate glasses composed of SiO 2, Al 2O 3, K 2O, Na 2O, BaF 2 and BaO. Structural characteristics such as size, shape, volume fraction and size distribution of nanoparticles in the glass matrix were studied by anomalous small angle x-ray scattering (ASAXS). Fitted ASAXS curves near the Ba absorption edge reveal the formation of a core-shell structure. Furthermore, ASAXS results allowed to determine quantitatively the composition of the nanocrystals, the surrounding region (shell) and the matrix. The evaluated composition gives evidence for an enrichment of Si atoms in a shell, that surrounds the particles and acts as a diffusion barrier. Resonant curve analysis reveals the quantitative information of the Ba atoms used in the formation of BaF 2 nanoparticles.