Brushite (dicalcium phosphate dihydrate, DCPD, CaHPO(4)2H(2)O) and whitlockite [WH, Ca9Mg(HPO4)(PO4)(6)] are usually found in the mammalian metabolism in the form of diverse pathological calcifications, dental calculi, urinary tract stones, salivary gland deposits, cardiovascular or pulmonary calcified deposits, and even as prostate or cartilage calcifications. The hydrothermal transformation of synthetic brushite crystals into single-phase whitlockite, octacalcium phosphate, or apatitic calcium phosphate was observed over the time period of 1 to 21 d and at 37 degrees C, 70 degrees C, and 115 degrees C in nonstirred physiologically relevant solutions developed for this work. The strong influence of the physiologically relevant ions such as Mg2+ and HCO3- on hydrothermal transformations is exposed. The formation of the nanoglobules and nanofibrils of X-ray amorphous calcium phosphate or Mg-doped calcium phosphate on the surfaces of brushite crystals are observed for the first time in biomimetic solutions containing 10 mm Mg2+ and/or 27 mm HCO3-. The experimental conditions leading to the formation of such nanofibrils on brushite crystal surfaces are also found to stop the further transformation of brushite into any other calcium phosphate (CaP) phases even at high solution temperatures. Samples were characterized by scanning electron microscopy and powder X-ray diffraction.