Hydroxyapatite (HAp) was separated from scales of fish by two different methods, i.e., calcining and treating with hot potassium hydroxide aqueous solution. The thermal change of the powders obtained by the two methods was investigated by thermo-gravimetry, differential thermal analysis and X-ray diffraction, and the Ca/P molar ratio was determined by chelatometry. HAp contained in the scales showed diffuse X-ray diffraction patterns due to low crystallinity and/or micro-crystallinity as well as existence of bone minerals. The values of Ca/P molar ratio of HAp obtained by calcining and by treating with alkaline solution were 1.57 and 1.63, respectively. The former decomposed into stoichiometric HAp (Ca10(PO4)6(OH2) and β-calcium orthophosphate (β-Ca3(PO4)2) at 800°C. The latter was stable up to 900°C and converted to well-crystallized HAp.
