X-ray diffraction analysis of sardine scale ash.

The scale ash of the sardine Sardinops melanosticta was analyzed by an X-ray diffraction method in order to identify the compounds in the minerals of the ash. The diffraction pattern of the scale ash was compared with those of five authentic chemicals with a molar ratio of Ca to P or of Mg to P of about 3 to 2, based on our previous results by chemical analyses. The peaks of the diffraction pattern of the scale ash did not coincide with any of the α and β types of Ca3(PO4)2, Ca3(PO4)2•nH2O, or Mg3(PO4)2•8H2O. However, the peaks of the diffraction pattern of hydroxyapatite (HAP) coincided with those of scale ash except at 31.2° and 34.6° where HAP had no peaks. The chemical, among the five authentic chemicals, which showed the peaks at 31.2° and 34.6° was β-Ca3(PO4)2. The X-ray diffraction pattern of the mixture of HAP and β-Ca3(PO4)2 in a molar ratio of 5 to 5 showed almost the same diffraction pattern as that of scale ash. Consequently, the main compounds in the sardine scale ash were estimated to be HAP and β-Ca3(PO2)4. The crystallization of HAP and β-Ca3(PO4)2 in the scale progressed by ashing at 600°C. On the contrary, the bone mineral of the sardine was regarded as almost pure HAP and was practically different from the minerals of the scale.