A Raman spectroscopic study of heat-treated nephrite

This study concerns the detection of heated nephrite jade, as some issues remain debatable: was heat-treatment used to facilitate jade carving or to modify jade's colour in ancient China? Has jade been burnt during funeral ceremony? Have forgeries been heat-treated to give the appearance of naturally weathered and altered jades? The understanding of the effect of heat on nephrite can provide useful information for answering these questions. Nephrite breaks down when heated above 840°C, and the phase transition is easily identified. However, detecting nephrite heated below 800°C was a challenging task as no principle crystal phase transition occurs. In this work, Raman spectroscopy is employed to study heated nephrite in a nondestructive way. For the first time, the subtle changes of molecular structure of nephrite heated below 840°C are reported in detail. The results show that the oxidation–dehydrogenation phenomenon is the key to understand the modification in heated nephrite.