it was mentioned above that c-HAp formation on xerogels surface is a gradual process. However, to observe the changes in xerogels morphology SEM analysis with XEDS were also used (Fig. 4). According to SEM–XEDS micrographs a progressive formation of c-HAp might be observed [17]. After 7 days of the bioactivity test in SBF, irregularly shaped flake-like precipitates of calcium phosphate appeared. They formed randomly distributed clusters, indicating a heterogeneous nucleation process. After 14 days, the calcium phosphate precipitates were organized into the larger spherical clusters. After 28 days, the composite surface consisted of a continuous porous apatite layer typical for apatite phosphates [18].