Therefore, we propose that the anisotropic growth of hydroxyapatite crystals and its dependence upon the hydrofluxes composition (water content, hydroxide content) is directly linked to the interaction between the hydroflux and the crystal facets. Indeed, Susman, Rimer, et al. observed that adding small amounts of water to a NaNO3:KNO3 (3:2 at.) molten mixture favored the growth of MgO crystals exposing rare {111} facets. Faceting was explained by the preferential interaction of water molecules with the {111} MgO facets. For the archetypal calcium phosphate hydroxyapatites, water interacts preferentially with the {100} facets, leading to preferential growth along the c axis. We observe herein a similar trend for a Mn(V) hydroxyapatite: the preferential [001] growth can be ascribed to stabilization of the {100} facets by interaction with water molecules that decrease their surface energy. Interestingly, foreign anions, including nitrate and chloride ions, seem to disturb the interaction of water molecules with {100} facets, possibly by competitive adsorption. These species could also change the local structure of the hydroflux, by preferential interaction with water, alkali cations, or hydroxide anions; We note that previous reports of Mn(V) hydroxyapatite syntheses used strontium chloride for precipitation in strongly alkaline aqueous solutions or strontium nitrate by hydroflux synthesis. In agreement with our interpretation, these works could not achieve anisotropic growth.