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GIA Discovers Spinel Treated by Nickel Diffusion

February 19, 2023  |  Anthony DeMarco
GIA spinel used 012923

Gemological Institute of America (GIA) scientists discovered spinel treated by nickel diffusion in a parcel of stones it examined in its New York lab — a new development in the colored-gemstone market, the organization said.

The GIA found the treated stones in a package of 24 spinels acquired for research purposes by a team in Bangkok, Gems & Gemology, its quarterly professional journal, recently revealed online. It will publish the report in the spring 2023 print edition.

Though the gems were said to be cobalt diffused, GIA researchers detected high concentrations of nickel, consistent with diffusion treatment, in some of the stones. The treatment with nickel, which has not been reported in gemological literature, caused a blue-to-green hue in pale-colored spinel, it explained. This was accompanied by artificial healing of fractures resulting from the heating process.

“Nickel-diffused spinel has not been seen before by GIA,” said Shane McClure, global director of colored-stone services. “Anyone examining spinel in this color range showing evidence of heat treatment should consider the possibility of nickel diffusion.”

While the cobalt gems have a deep blue color, the nickel-treated gems have “lighter blue, greenish-blue, bluish-green, or blue-green color,” the GIA commented.

Using advanced spectroscopic equipment, GIA researchers discovered indications of nickel-related absorption in natural spinel, the GIA said. Other key indicators of the nickel absorption treatment are color concentration at facet junctions, photoluminescence spectra indicating heat treatment, and abnormally high amounts of nickel.

Nickel-diffused treatment isn’t more or less significant than cobalt-diffusion or other diffusion treatments, gemologist Gary Roskin of the Roskin Gem News Report told Rapaport News. Yet it is another treatment that affects the gem’s value.

Because some of the treatments were just inside the surface of the stone, it could have a detrimental effect on the spinel’s appearance later, Roskin noted.

“If the stone needs to be repolished it could remove the treatment and most likely affect the appearance and value of the stone,” he observed.

The GIA first reported on spinel treated by cobalt diffusion in 2015. Examination for the treatment, which yields a vibrant blue hue, is part of the organization’s gemological service for spinel.

Image: The nickel-diffused spinel. (Aaron Palke and Diego Sanchez/GIA)

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GIA spinel used 012923 GIA Discovers Spinel Treated by Nickel Diffusion

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