Provenance studies of emerald: Evaluation of a Raman approach

Emerald is the more prestigious gem among the beryl-group minerals. Mineralogically, it is a cyclosilicate of Al and Be with general formula Be3Al2Si6O18. The presence of Cr3+ and V3+ determines the typical green color. The particular structure is composed by tetrahedra (Si6O18) forming six-member rings, stacked along c -axis, forming continuous channels where ions (alkali) and molecules (water) can be present. Recent studies used spectroscopies in the provenance study of emeralds. In particular, on the basis of shape and position of vibrational features associated to the Si-O vibration (1067-1072 cm-1) and those of water (3300-3800 cm-1), it could be possible define the genetic model for each deposit and consequently the emerald provenance. The present work is aimed to define a non-invasive procedure that could be applied in provenance studies of emeralds. In particular, the results of a Raman study on samples from the main deposits exploited in antiquity such as Malyshevsk (Russia), Jos (Nigeria), Pajshir Valley (Afghanistan), Habactal (Austria), Sikait, Zabara (Egypt) and Swat Valley (Pakistan) are reported. The spectroscopic markers connected to the different deposits are compared to the genetic models proposed by Aurisicchio et al. (2108). Therefore, a comparison among spectroscopic and chemical data can give an overview about the potentiality of the Raman spectroscopy.