Structural Analysis of Precious Coral Carbonate Layers Using Synchrotron Radiation-infrared Rays

Abstract

Carbonate skeletons of precious corals, other corals and a giant clam were analysed by synchrotron radiation-infrared spectroscopy (SR-IR) at beam line BL43IR, JASRI (SPring-8) to establish necessary basic technologies for the sustainable use and control of the trade of precious corals. Precious and bamboo corals differed from hump and stylasterina corals and giant clam in microspectroscopic spectra of the axes. The spectra of the former showed a particular type of calcite, whereas the later spectra indicated an aragonite. The spectrum of a deep-sea coral collected from off Midway Is. is different from that of other precious corals. Also that of a deep-sea coral collected from off Ogasawara Is., Japan was different from other corals in the spectra of sclerites. As a result of synchrotron infrared mapping analysis in the cross-section of precious coral axis, changes in the absorbance were observed at some wavenumbers. The cycle of fluctuation ranged from 109.23 to 147.17 μm. The fluctuation was considered to be an annual change. Therefore, the radial growth rate of precious coral axis was estimated to 0.22–0.35 mm year⁻¹. This study indicates that synchrotron radiation-infrared spectroscopy analysis is effective to differentiate a genuine from a fake precious coral and to estimate the growth rates of precious corals.