摘要
中国古代出土玉器常伴有白化现象,此现象在三星堆遗址出土玉石器中较为常见.本研究采用X射线衍射仪、激光共聚焦显微拉曼光谱仪、傅里叶变换红外光谱仪、同步热分析仪等分析三星堆遗址出土白化玉器.结果显示三星堆遗址出土白化玉器主要物相为方解石及透辉石——透辉石可由透闪石受热转化而成,玉器白化与受热有关.透闪石玉由高温热液流经镁质碳酸岩通过交代作用而形成,镁质碳酸盐岩中富含晶包有机质,推测透闪石玉中同样含有晶包有机质.本研究中玉石的荧光光谱及加热、溶出等模拟试验均证明了这一推论.方解石与透闪石玉内均含有分散有机质,玉石白化不仅取决于玉石结构变化,还与玉内分散有机质流失有关.
Abstract
The phenomenon of whitening is frequently observed in ancient jade artifacts unearthed in China,with a particularly high prevalence at the Sanxingdui site.In this study,X-ray diffraction(XRD),laser confocal micro-Raman spectrometry(Raman),Fourier transform infrared(FTIR)spectrometry,and simultaneous thermal analysis were used to analyze whitened jades excavated from the Sanxingdui site.The XRD results indicate that the primary phases of the whitened jades were calcite and diopside—the latter can be generated through the transformation from tremolite with heat.The Raman result indicates the presence of a pronounced hump-shaped fluorescence background for the jades.This type of fluorescence is more prevalent in carbonate minerals with elevated levels of sedimentary organic matter.The formation of tremolite jade is a consequence of high-temperature hydrothermal fluid flowing through magnesium carbonate rock.During the diagenetic transition,the dispersed organic matter in magnesium carbonate rock is partially retained in the tremolite.Carbonatite minerals and tremolite jade contain a certain amount of crystal-enclosed organic matter in addition to the presence of adsorbed organic matter.The content of the crystal-enclosed organic matter in tremolite jade is relatively lower,with a release temperature of 900-1 150℃.This organic matter is primarily composed of ammonium or magnesium salts of waxes and resins.Tremolite jade loses its greasy luster and gets whitened after the loss of crystal-enclosed organic matter.The oxidation or polymerization of the dispersed organic matter within the jade will increase the carbonyl(C=O)functional groups in the organic molecules,and the increase of unsaturated bonds will cause a conjugation effect of the organic molecules within the jade,with the fluorescence intensity being geometrically increased.Modern coal petrology employs a range of technologies,such as the fluorescence one,to microscopically identify visible dispersed organic matter in sedimentary rocks through optical microscopy.The Raman spectrometer is capable of simultaneously receiving both Raman scattered light and fluorescence because the fluorescence signal generated by laser excitation is stronger.This makes it a more suitable instrument for the identification of trace dispersed organic matter in minerals.When the 785 nm laser of a Raman spectrometer is used to irradiate jade,the fluorescence generated by carbonyl conjugation will form a hump-shaped fluorescence background in the Raman spectrum of jade.This type of fluorescent background is prevalent in jades unearthed throughout China and is particularly evident in fire-labored jades.The jade artifacts unearthed at the Sanxingdui site were discolored due to heating.This process was dependent on both the structural changes of a jade itself and the loss of dispersed organic matter within the jade.Due to the presence of burning traces in the sacrificial pits at the Sanxingdui site,the excavated whitened jades display a uniform and fine texture,accompanied by a pronounced fluorescent background in the Raman spectra.It could be surmised that the jade artifacts from the Sanxingdui site were directly buried during the burning process.The high pressure caused by the residual temperature in the pit and the vaporization of materials in a confined space after burial made it easier to release the crystal-enclosed organic matter within a jade while the integrity of jade artifacts was kept.The released organic matter was retained in the sacrificial pit.In a confined space,the elevated temperature and oxygen-deficient environment prompt the crystal-enclosed organic matter in jade to undergo polymerization and absorb some visible light,thereby inducing a transformation in the surface color of jade.
基金项目
山东省青年文博人才培养项目(2024YFFK0125)
四川省科技计划重点研发项目(2024YFFK0125)
万方数据