Petra Stock
Researchers have used modern tools to analyse the unique chemical composition of ancient gemstones, tracing samples of peridot, emerald, amazonite and amethyst back to their original source.
Publishing in AIP Advances, researchers from Egypt and Saudi Arabia used three modern spectroscopy techniques, to unveil unique characteristics of gemstones originally mined from the Middle East, distinguishing these from minerals from other sites and from synthetic gems.
A number of gems analysed were sourced from a geological site called the Arabian-Nubian Shield in the Middle East, an area containing mineral deposits of precious metals and gemstones that have been mined and traded for thousands of years.
“This includes a variety of silicate gems such as emerald from the ancient Cleopatra’s mines in Egypt, in addition to amethyst, peridot, and amazonite from other historical sites, which mostly date to the Roman times,” says author Professor Adel Surour from Galala University.
They also analysed gems from around the world.
The authors used Laser-induced breakdown spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy – each technique using the absorption and emission of electromagnetic radiation to reveal information about each gemstone.
Laser-induced breakdown spectroscopy characterises chemical composition using a high energy laser to identify the concentration of different elements within a mineral sample.
Fourier transform infrared spectroscopy uses infrared radiation and reveals information about chemical composition, such as molecules rather than just elements. It can be used to identify characteristics like the presence of water and other hydrocarbons.
The third technique, Raman spectroscopy, uses a type of monochromatic light, which reveals information about the internal structure of the gemstones.
The three spectroscopic techniques to revealed the unique chemical composition of each gem, down to the crystalline structure of the gem’s atoms.
“We showed the main spectroscopic characteristics of gemstones from these Middle East localities to distinguish them from their counterparts in other world localities,” says author Surour.
The results show that iron content correlates to amethyst’s signature purple hue. Elements such as copper, chromium, and vanadium also provide colour.
Synthetic gems can be identified by a signature water peak. These lab-grown minerals, are otherwise identical to natural gems but less expensive.
Amazonite beads mined from Mexico, Jordan, and Egypt each had their own unique crystalline structure.
“Gemstones such as emerald and peridot have been mined since antiquity,” Surour says.
“Sometimes, some gemstones were brought by sailors and traders to their homelands. For example, royal crowns in Europe are decorated with peculiar gemstones that originate from either Africa or Asia. We need to have precise methods to distinguish the source of a gemstone and trace ancient trade routes in order to have correct information about the original place from which it was mined.”
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