Professional Jeweler Archive: Study in Red

October 2001

Gemstones & Pearls/Gemology


Study in Red

Madagascar's rubies have a unique set of fingerprints


Madagascar’s new ruby finds in Vatomandry and Andilamena are proving the inclusions scene in these gems is far from dull. “These characteristics also help differentiate them from other rubies,” says Ken Scarratt, director of the American Gem Trade Association’s Gemological Testing Center, New York City. Using gem microscopy and micro-Raman analysis, Scarratt peered into the internal world of several Madagascar ruby samples.

One interesting feature, he notes, is what appear to be “breadcrumb” inclusions observed under low-power magnification. However, high-magnification and micro-Raman spectroscopy reveal them to be small rounded natural crystals that Scarratt identifies as zircon clusters. He says these groupings appear to be typical of unheated Madagascar rubies. Trace analysis also reveals high concentrations of iron.

This combination of characteristics – breadcrumb inclusions and high iron – helps distinguish rubies from Madagascar from those of other localities, such as Myanmar.

The Madagascar rubies have rounded and larger crystals with rutile and apatite inclusions. But such inclusions are common also in rubies from elsewhere so are not diagnostic.

Inconclusive Proof

The AGTA Lab detected glassy residue in many of the Madagascar rubies it studied – these are diagnostic of traditional heat treatment.

But some observers say a non-traditional, low-temperature process is involved because the treatment doesn’t appear to alter zircon or apatite inclusions or, most importantly, rutile needles, says Scarratt. “The alteration or dissolving of these needles has been used as a guide to whether corundum [of which ruby is a variety] from other localities is heated,” he says. “Observing intersecting rutile needles in a Madagascar ruby does not preclude it from being a heated stone.”

• AGTA Gemological Testing Center, New York City; (212) 752-1717, www. agta.org.

– by Robert Weldon, G.G.

All photos are courtesy of Ken Scarratt
AGTA Gemological Testing Center, New York City

At 10X, clusters of “breadcrumb” inclusions are visible among the rutile needles.
Higher magnification reveals the “breadcrumbs” are actually clusters of rounded crystals identified as zircon.
The presence of glassy residue – seen as a network of droplets within a fissure – is characteristic of ruby heat treatment.
Rutile crystals (center, right) appear only slightly altered by heat treatment.
Some crystals in Madagascar ruby are more vulnerable to heating – this hexagonal crystal appears to have exploded.
Fine rutile needles in a heated Madagascar ruby appear largely unaltered by heating. This may force gemologists to rethink the observation that intersecting needles mean a ruby has not been heat-treated.

Copyright © 2001 by Bond Communications