Mg2SiO4 fishbone-like fractal nanostructures have been investigated using high-resolution transmission electron microscopy. The branches of Mg2SiO4 fibers and detailed structures of cobalt nanoparticles at different growth stages have been recorded, and the formation mechanisms of both the fibers and the Co nanoparticles are discussed. It was found that these two components grew concurrently. Co initially formed nanocrystallites with sizes less than 5 nm and these nanocrystallites joined together to form spherical clusters. These clusters continued to grow and recrystallized into larger polygonal single crystals (>150 nm). The experimental evidence shows that the formation process of Mg2SiO4 includes amorphous surface coating, forming polycrystallites in the coating layer and recrystallizing into cylindrical main stems and branches.