Civilizations have traded emeralds since antiquity, but the sources of many famous gems have remained unknown. Not only is it hard to judge a stone's origins from its external characteristics, but historical records are confusing in many cases. For instance, scholars attributed the "old mine" emeralds, distributed by Indian traders in the 16th century, to mines in Southeast Asia, but such deposits were not officially found until several hundred years later.

Image: K. LEUTWYLER, after GIULIANI et al. in Science

NINE EMERALDS, represented here as white boxes, hark from a variety of different mines (dark green bands), based on their ratio of 18O to 16O (x-axis). A Gallo-Roman earring's gem (1) comes from Pakistan. The St. Louis stone in the crown of France (2) is from Habachtal in Austria. Hauy's emeralds (3) are from Austria and Egypt. Gems from the Nuestra Seora de Atocha come from Colombian mines (top four sources), as do three Nizam stones (5). Another is from Afghanistan.

Now, however, a group of French and Colombian scientists have cleared up some of the mystery. Using a new technique, Gaston Giuliani of the Institut de Recherche pour le Dveloppment and the Centre de Recherche Ptrographiques et Gochimiques-CNRS, Marc Chaussidon, also of CRPG-CNRS, and their colleagues revealed the birthplace of nine well-known stones. Their results appear in the January 28 issue of Science.

Image: Topkapi Palace

TOPKAPI DAGGER, from Topkapi Palace in Turkey, is studded with emeralds that, like the stones in other Old World treasures, may have originated in the New World.

They have found that some of the "old mine" emeralds in fact came east by way of Colombia, ferried across the Atlantic by Spanish conquistadors. And other valuable gems presumed to be from Egypt or Austria--the only documented emerald mines in the world before 1545 A.D.--actually sprang up from the Middle East.

The oldest gems the group analyzed included part of a Gallo-Roman earring, recovered from a site in Miribel, France; two emeralds used by mineralogy's founder, Abb Hauy, to describe the gem in 1806; and the St. Louis emerald in the Holy Crown of France. More modern stones also came under scrutiny: four emeralds from the treasury of the Nizam princes of Hyderabad, India; and a rough emerald retrieved from the wreck of the Spanish galleon Nuestra Seora de Atocha, which sank near Florida in 1622.

In the study, an electron ion beam bombarded each emerald, thereby dislodging oxygen ions from the gem's crystal lattice. The group was interested in the ratio of 18O to 16O. Because these isotope levels reflect the composition, temperature and surroundings of the liquids that crystallize into emeralds, they vary little at one mine but change dramatically from one source to another. Thus, they serve as a kind of gemstone fingerprint. These isotope values range from 6.2 to 24.8 percent for all known emerald deposits--and those in this analysis were nearly as far flung.

The isotope data confirmed some historical notions. For instance, the Holy Crown and Hauy emeralds did originate in the Austrian Habachtal mines, as might be expected. But the Gallo-Roman earring stone was born in the Swat-Mingora district of Pakistan, a previously unknown source in antiquity. And three of the Hyderbad emeralds came not from the east but from separate mines in Colombia (Pea Blanca, Coscuez and Tequendama), suggesting that Spanish trade had a broader reach than we knew.

"Colombian emerald deposits are unique in the world, producing stones with richer color, clarity and bigger crystals than most emerald deposits," Giuliani notes. "We imagine that these were the qualities that the Spanish, and the rest of the world, were interested in." His group speculates that many of the treasures found today in India, Turkey and Iran came predominantly from New World mines. Next, they are looking at rubies.