In this paper, amorphous calcium phosphate (ACP) with an increasing Ca/P molar ratio (Ca/P ratio of 1.67, 2.0, 2.2, 2.4, 2.6 and 2.8) were synthesized, freeze-dried and then crystallized. Crystallization was achieved in three ways: in a hydrothermal bomb at an elevated temperature and pressure in water or steam, and in a furnace at an elevated temperature. The crystallization temperature of synthesized powders was determined by differential thermal analysis (DTA), Fig 1, and qualitative phase analysis conducted from X-ray diffraction (XRD) patterns. A series of crystallization routes have been examined to see which pathway holds the most calcium while retaining a monophasic apatite.