The Nature of the Pigments in Corals and Pearls: A Contribution from Raman Spectroscopy

Raman measurements at 473.1nm on corals, both calcitic and aragonitic, and on pearls (aragonitic) were performed to elucidate the nature of the pigments, with the relative importance of methylated (carotenoids) or nonmethylated polyenes involved in the color associated with marine mineralized organisms still being a debated question. The resonance condition of the laser excitation enables the observation of overtones and combinations of four main vibrational modes of the polyenic or carotenoid pigment up to >5000 cm(-1). Raman spectroscopy proves to be a powerful tool to determine the biomineralized structure, the nature of the pigments, and the presence of artificial dyes.