Evaluation of emeralds by their origin: Multivariate analysis - Infrared spectra

Abstract

Colombian emeralds, 26 from Palo Arañado (eastern emerald zone, Chivor district, Boyacá, Colombia), and 28 from Santo Domingo - La Pava mine (western emerald zone, Muzo district, Boyacá, Colombia), together with 30 from Kafubu - Zambia, were studied by reflectance Fourier transform infrared spectroscopy, principal component analysis, clustering, and partial least squares – discriminant analysis, in order to differentiate them by geographical origin. The spectra were smoothed and a baseline correction was made. The principal component analysis showed that the wavenumbers 2,474; 2,640; 2,686; 2,818; 5,448, and 6,815 cm-1 are the most significant in the first principal component and the most valuable in separating the emeralds by their geographical origin. This allowed us to completely discriminate emeralds from Santo Domingo and Zambia, while only five emeralds from Palo Arañado were 100 % differentiable from the other two groups of emeralds.