μ-Raman as a fundamental tool in the origin of natural or synthetic cinnabar: Preliminary data

This paper is a preliminary study on the origin of the precious red pigment cinnabar by μ-Raman analysis. The importance of this pigment is partly due to its low availability. When the mineral was used in the Roman Age, the district of Almadén, Spain, was probably the most exploited region. However, it is still not well defined if further ores were chosen for supply. A scientific methodology has to be assessed. In the present study, samples with known provenance (Spain, Slovenia, Italy, Russia, China, and minor European deposits) were collected from Italian Mineralogical and Earth Science Museums. μ-Raman analysis was chosen to acquire structural data, which were finally treated by statistical analysis. Most of the samples from China were characterized by the presence of selenium. This was proved by the additional band at ~200 cm−1. The statistical analysis of Raman data suggests that the position of the most intense band at ~252 cm−1 also influences the discrimination of the Chinese samples. This work also demonstrates that a higher purity may be revealed by μ-Raman analysis, eventually leading to the discrimination of natural sources from synthetic cinnabar. It also proves that the most common exploitation sites, Almadén and Idrija, may be statistically distinguished. Despite its exploratory nature, this study is intended as a successful preliminary step to gain information of provenance from a single, potentially non-destructive technique, such as μ-Raman spectroscopy.