Non-Destructive Study of Egyptian Emeralds Preserved in the Collection of the Museum of the Ecole des Mines

Abstract

In the present study, rough emerald single crystals and rough emeralds in the host rock from the ruins of Alexandria and from the Mount Zabargad in Egypt, preserved in the collection of the museum of the Ecole des Mines (Mines Paris—PSL) since the late 19th or early 20th century, are investigated. All samples were characterized by non-destructive spectroscopic and chemical methods during a week-long loan to the LFG. Raman, FTIR and UV-Vis-NIR spectroscopy revealed that Egyptian emeralds contain H2O molecules accompanied by relatively high concentrations of alkali ions and are colored by chromium and iron. Additionally, EDXRF showed that the emeralds from Egypt contain up to 84 ppm Rb and low amounts (below 200 ppm) of Cs. Inclusions and parts of the host rock were also observed under optical microscope and analyzed with Raman spectroscopy. Tube-like structures, quartz, calcite, dolomite, albite and phlogopite are associated minerals, and inclusions are identified in these historic emeralds from Egypt. This work will hopefully further contribute to the characterization of emeralds of archaeological significance.