The one-step synthesis of carbonated hydroxyapatite (CAP) using calcite and different orthophosphates was investigated in a closed batch reactor. Only orthophosphoric acid could lead to the complete decomposition of calcite particles, when the reaction temperature was set at 80 degrees C. On the other hand, the reaction time and the dilution of the initial calcite suspension had no significant influence on the formation of the solid products. CAP was formed as the main crystalline calcium phosphate with the carbonate content in the range of 4.2-4.6 wt.%. The thermal decarbonation of the synthesized CAP started at 750 degrees C but it was only significant at 1000 degrees C under air atmosphere. This thermal decarbonation was total at 1200 degrees C or above. All CAP samples and products following thermal treatments were found bioactive in the test using simulated body fluid (SBF) solution. (C) 2014 Elsevier Ltd. All rights reserved.