Identification of cinnabar existing in different objects using portable coupled XRF‑XRD, laboratory‑type XRD and micro‑Raman spectroscopy: comparison of the techniques

摘要

Cinnabar (alpha-HgS) is a common mineral used in various fields. The identification of cinnabar can be achieved by classic mineralogical methods and instrumental methods. X-ray diffraction (XRD) is the most reliable instrumental method for identifying material phases, but the sampling process and the immovable instrument limit its wider application in the cultural heritage field. The occurrence of Assing S. p. A. Surface Monitor, a portable system integrating X-ray fluorescence (XRF) and XRD, provides researchers with a new solution. Raw mineral, polished gemstone, pigment powder and Chinese ink stick claimed to be composed of cinnabar were measured by the system as well as laboratory-type XRD and micro-Raman techniques in this study. The qualitative XRF results were applied to determining the elements existing in the samples and thus defining the range of possible phases. Patterns obtained were compared carefully with the characteristic lines to determine the most likely phases, while the pattern appearances were compared in order to recognize the different states of cinnabar and generalize the experience for identifying cinnabar by the system. The Raman spectra obtained were compared and analyzed in order to learn the best parameters and determine the real composition of each sample. The results indicate that the XRF detector is sensitive enough to distinguish cinnabar from another red pigment, minium (Pb3O4), without destructive preparation provided that the desired phases occupy a major content in the sample, while the laser micro-Raman is even better in application range and measurement speed but correct analysis of the spectra is highly dependent on experience and literatures. The portable coupled XRF-XRD system and the micro-Raman provide researchers with convenient and efficient options to preliminarily identify minerals like cinnabar, which is significantly meaningful to several research fields including mineralogy, heritage science, material science, etc.