Going Inside a Historical Brazilian Diamond from the Spada Collection (19th Century)

The characterization of objects of historical and cultural interest represents a crucial topic, specifically when it regards gemstones. Actually, the advanced investigation of precious minerals of gemological interest requires exclusively non-destructive analyses which are also suitable for determining their provenance when it is unknown. In this study, a non-destructive analytical protocol, previously tested on diamonds for petrogenetic studies, has been applied to a natural diamond of very high historical and gemological value, donated in 1852 by Monsignor Lavinio de ‘Medici Spada to the Museum of Earth Sciences of Sapienza University (Rome). The analytical protocol used includes X-ray diffraction topography, micro-computed X-ray tomography, single- crystal micro-X-ray diffraction and Fourier-transform infrared spectroscopy. The results show the presence of dislocations originating from inclusions and a very low degree of plastic deformation. The aggregation states of its N impurities show that this diamond is type IaAB, while the inclusions consist of olivine (Fo92-93), suggesting a lithospheric origin. The historical references found in the catalogs of the Museum indicate only a Brazilian origin, without any reference to the mining district. The information acquired in this study, enhanced by document research on mining in Brazil since 1700, suggests that the diamond likely comes from the district of Diamantina, Mina Gerais, Brazil.