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Friday, 28 January, 2000, 15:50 GMT
Scientists break emerald myths

The research is reported in Science magazine

A careful analysis of some of the world's most magnificent emeralds has shown the gem stones have secret histories.

Three of the stones belonging to the collection of the Nizam of Hyderabad, an ancient Indian family, actually came from Colombia in the 16th Century and not, as legend tells, from Alexander the Great many years earlier.

For more than 4000 years, the deep green of a flawless emerald has been treasured around the world as a symbol of eternal spring and immortality. The gemstone has been prized by the Egyptians, Romans - Emperor Nero surveyed the gladiators through an emerald monocle - the Moguls of India, the Aztecs, and the crowned heads of Europe, among others.

But the history of many of the world's best gems is often shrouded in myth and difficult to trace. This led a team of researchers from France and Colombia to use the latest analytical techniques to determine the origin of nine famous stones that span a period from the Roman occupation of France until the 18th century.

The study involved vaporising a microscopic portion of a stone with a laser and then analysing the isotopes, or different types, of oxygen atoms given off.

Composition and temperature

Oxygen isotope values in gems such as emeralds reflect the composition and temperature of the fluids that eventually crystallised to form the emerald, as well as the composition and temperature of the rocks that the fluids journeyed through before their consolidation into the gemstone.

There is a narrow range of these isotope values for each site where emeralds have been discovered worldwide.

Along with more traditional gemological aspects, such as optical properties and the inclusion of other materials, researchers can use these unique isotope values to pinpoint where an emerald was "born."

The researchers, led by Gaston Giuliani of the Institut de Recherche pour le Développement and the Centre de Recherches Pétrographiques et Géochimiques-CNRS in Vandoeuvre, France, tested stones from all of the world's major emerald mines.

Major surprises

They found that some ancient emeralds came from deposits supposedly discovered in the 20th Century, showing that these mines were known as far back as Roman times.

A major surprise was the number of gems from Colombian mines. These emeralds were only traded worldwide after the Spanish invasion of Latin America in the 16th Century.

Yet, three of the four major emeralds analysed from the collection of the Nizam of Hyderabad in India, supposedly from "lost" Asian mines, were actually from Colombia and not as legend tells from Alexander the Great (around 300 BC).

The researchers now plan to apply the oxygen isotope technique to studying rubies.

"This type of analysis was a small part of our work initially," said Giuliani. "But we see that as geologists working with gemstones and gemologists, we may be permitted to make a contribution to the study of trade and human history."

The research is reported in the journal Science.

India The Nizam ruled Hyderabad until 1948

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14 Nov 98 |  South Asia
Battle for jewels of Nizam

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