Study on the secondary changes of jades from Fubin culture (3200–3000BP) in Lingnan, China.

Some seriously weathered jades of Fubin culture were unearthed at the Moyishan site in Lingnan, South China. These long-buried jades have many secondary changes such as discoloration, microstructural change and chemical composition variation. To explore the formation mechanism of secondary changes, the microstructure, mineral components, and chemical content of the jade samples and their buried soil are analyzed separately. The jade with red-brown shell is preserved well and shows better structural stability, further research indicates that it's the result of surface complexation reactions. During the long-term burial in acidic soil environment, the jade wrapped in the negatively charged kaolinite which absorbed Fe3+ to complexed on the jade surface. Iron(ⅲ) precipitates causes the dense shell to appear red-brown. [ABSTRACT FROM AUTHOR]