Functionalized-inorganic powders were obtained by the chemisorption of a series of substituted trimethoxysilanes on the surface of spherical and hexagonal hydroxyapatite crystals. The highest total loading for all trimethoxysilanes was achieved for the hydroxyapatite (CaHAP) of spherical morphology. For hexagonal CaHAP, the loading decreased with an increase in the length to diameter ratio from 0.5 to 11. Thus, the different faces of the crystal are not equally reactive: {0001} planes are more reactive than {1010} planes.