Emerald Analysis Reveals Gems' Long Journey
- By Nicholas Wade
- Jan. 29 2000 00:00
Emeralds, the precious stones sought after for centuries to grace maharajahs' and sultans' turbans and the crowns of European kings, have yielded an insight about their origins to a team of French researchers.
By analyzing inherent traces of the water from which the stones crystallized eons ago, the researchers say they can identify the country and even the individual mine from which an emerald came.
The French method has helped delineate the routes by which emeralds were traded in the ancient world, and may also influence present day prices for the stones, which are often deemed more valuable if their provenance is known.
The only sources of emeralds before the discovery of the New World were thought to be Cleopatra's mine in Egypt and a small mine discovered by the Romans in the Austrian Alps. But analysis of the emerald in a Roman earring found in France showed it must have come from a mine in Pakistan, perhaps from the ancient kingdom of Gandhara, and would have reached Europe along the Silk Road, the French scientists say in a report in Thursday's Science.
The emerald analysis method was developed by Dr. Gaston Giuliani of the Center for Petrographical and Geochemical Research in Vandoeuvre-les-Nancy, France, and colleagues elsewhere.
It depends on vaporizing a small sample from the surface of the stone so as to measure the ratio of oxygen isotopes. The oxygen is derived from the hot waters out of which the emeralds crystallized, and each of the few known mines in the world seems to have had water with different isotope ratios. Isotopes are atoms of the same element that differ in the number of neutrons they contain.
The vaporization leaves a minute pit in the emerald's surface. Even though the pit is invisible to the naked eye, the method is to that extent destructive. Giuliani said the director of the Museum of Natural History in Paris let him experiment first on two emeralds owned by the Abbe Hauy, the founder of mineralogy, which turned out to come from the old Roman mine in the Austrian Alps.
Giuliani's team was then allowed to test a precious relic, the emerald set on the central jewel lily of the Holy Crown of France by Louis IX. St. Louis' emerald too proved to come from the Austrian mine.
A new source of emeralds was opened up when the Spanish, after much torture and protracted fighting, discovered the Colombian mines that were the source of the emeralds found in Mexico and Peru.
Giuliani tested a smuggled emerald - it was not listed on the manifest - salvaged recently from the Nuestra Senora de Atocha, a Spanish treasure galleon that foundered off Key West in 1622. The oxygen isotope test showed the emerald came from the Tequendama mine of the Muzo district of Colombia.
Once the Colombian mines were in their possession, the Spanish started to develop buyers for the emeralds and found considerable interest among the rulers of India, Persia and Turkey. "So sultans, shahs and maharajahs were the principal market," said Fred Ward, a gemologist and author of the book "Emeralds."
The Spanish at first shipped the emeralds from Spain, then sent them via the Philippines. In India, the Philippines was long believed to be their source of origin, Ward said.
Giuliani's team tested four emeralds from the treasure of the Nizam of Hyderabad. He reports that three of the emeralds came from Colombia, each from a different mine, and the fourth probably from the Pansher Valley of Afghanistan.
Ward described the French method as a "dramatic innovation" that could affect the emerald market because of owners' interest in the stones' provenance. "If someone can say definitively an emerald is from a certain mine it may cause the emeralds to be more pricey," he said.
Emeralds at present are sourced by a battery of visual and spectroscopic tests that are indicative rather than definitive. "We regard origin as a professional opinion rather than a scientific fact," said Dr. Kenneth Scarratt, director of the testing laboratory at the American Gem Trade Association in New York.
Scarratt praised the French team's study but said more samples would be needed to validate the method. Even if it proved reliable, the fact that even a minuscule part of the stone was destroyed might deter clients who did not want to take the risk, he said.