Perfect vivianite crystals excavated from a highly sealed ancient tumulus in Jing'an County, Jiangxi Province, China

摘要

Large amounts of perfect crystals were excavated from ancient coffins dating 2510 (+/- 50) bp, in Jing'an County, Jiangxi Province, China. The coffins were wrapped by multiple bamboo mats and sealed highly by waterproof soil layers. In this study, crystals, wooden coffins, surrounding water and clay materials of several buried wooden coffins were subject to various analyses, and the crystals were identified to be vivianite by single crystal X-ray diffraction, X-ray fluorescence (XRF) and infrared (IR) spectroscopy. Spatial distribution of the vivianite crystals, which was consistent with first Fick's diffusion principle, indicated that the phosphate (PO43-) of the vivianite was originated from human bone that was demineralized under an acidic clay condition. Spatial distributions of iron(III) oxide (Fe2O3) and iron(II) oxide (FeO) indicated that iron(II) cations (Fe2+) of the vivianite originated from clay outside the coffins. Perfect vivianite crystals were formed at an extremely slow rate within the highly sealed coffins, in which Fe2+ and PO43- concentrations were of such a low level that the rapid precipitation of imperfect vivianite crystals was prevented, as the clay colloid could infiltrate only along the limited passageways of jointed seams between two halved timbers of the coffins.