In the present study calcium hydroxyapatites enriched at 0.08wt% in Mn2+ ions (Mn-HA) and their unsubstituted forms (HA) were synthesized using the same standard wet chemical route. Mn-HA and HA were both calcined at 800 degrees C to give Mn-HAc and HAc, respectively or sintered at 1250 degrees C, to give Mn-HAs and HAs, respectively. The influence of the heat treatment on physicochemical properties of Mn-HA was investigated using powder X-ray diffraction (PXRD), scanning, and transmission electron microscopy (SEM and TEM), and solid-state nuclear magnetic resonance (ssNMR). Mn-HAc and Mn-HAs were compared to each other and to HAc and HAs, respectively. Assignment of the proton ssNMR peaks from high-temperature-treated apatites has been revised. It was found that Mn-HAc and HAc were nanocrystalline, while Mn-HAs and HAs comprised micrometer sized, partially fused particles (SEM and TEM). PXRD and ssNMR demonstrated that the incorporation of Mn2+ into the crystal lattice of hydroxyapatite significantly facilitates its dehydroxylation and decomposition to oxyhydroxyapatite during calcination at 800 degrees C, and induces its transformation to tetracalcium phosphate (TTCP) and alpha-tricalcium phosphate (-TCP) at 1250 degrees C. Contamination by CaO has also been detected. The (HP)-H-1-P-31 NMR cross-polarization experiments have indicated that the Mn2+ ions preferentially occupied the Ca(I) position in the crystallographic unit cell of Mn-HAc. In Mn-HAs, the Mn2+ ions were evenly distributed between the Ca(I) and Ca(II) positions.