Microscopic characteristics and analysis of corroded jade artifacts from the Sanxingdui sacrificial pits in Guanghan, Sichuan Province

The Sanxingdui site in Guanghan, Sichuan, represents a significant archaeological discovery in southwestern China. The jade artifacts unearthed from its sacrificial area exhibit notable variations in preservation, with some showing severe whitening and powdery deterioration. Representative jade samples unearthed from sacrificial pits were selected, and their corrosion characteristics were studied by using optical microscopy, scanning electron microscopy-X-ray energy dispersive spectrometry (SEM-EDS), and Raman spectrometry. The results indicate that some jade artifacts had undergone heating processes prior to burial. In the tremolite jade artifacts that were partially pyroxeneized at high temperatures, the corroded areas are loose, with crystals exposed within the corrosion holes. Severely powdered and whitened diopside was formed through the thermal transformation of tremolite, exhibiting fractured morphologies and numerous pores. The whitened calcite jade artifacts are also heavily corroded, with fissures throughout the material and various inclusions, such as mica, hematite, and quartz-calcite mixtures. Furthermore, diverse crystal structures were observed in the whitened calcite, which may be closely related to its recrystallization process after heat treatment. Understanding the corrosion and deterioration mechanisms of these jade artifacts can provide valuable insights into their proper conservation and preservation.