Vibrational spectroscopic characterization of growth bands in Porites coral from South China Sea

A series of samples from different growth bands of Porites coral skeleton were studied using Raman, infrared reflectance methods. The Raman spectra proved that skeleton samples from different growth bands have the same mineral phase as aragonite, but a band at 133 cm(-1) for the top layer shows a transition from similar to 120 cm(-1) for vaterite to similar to 141 cm(-1) for aragonite. It is inferred that the vaterite should be the precursor of aragonite of coral skeleton. The positional shift in the infrared spectra of the skeleton samples from growth bands correlate significantly to their minor elements (Li, Mg, Sr, Mn, Fe and U) contents. Mg, Sr and U especially have significant negative correlations with the positions of the antisymmetric stretching band v(3) at similar to 4469 cm(-1). And Li shows a high negative correlation with v(2) band (similar to 855 cm(-1)), while Sr and Mn show similar negative correlation with v(4) band (similar to 712 cm(-1)). And Mn also shows a negative correlation with v(1) band (similar to 1082 cm(-1)). A significantly negative correlation is observed for U with v(1) + v(4) band (similar to 1786 cm(-1)). However, Fe shows positive correlation with v(1), v(2), v(3), v(4) and v(7) + v(4) bands shifts, especially a significant correlation with v(1) band (similar to 1082 cm(-1)). New insights into the characteristics of coral at different growth bands of skeleton are given in present work. (C) 2013 Elsevier B.V. All rights reserved.