The Gemological Institute of America (GIA) recently studied a very-light-pinkish-brown diamond with an atypical color center.
The GIA analyzed the pear brilliant, 5.22-carat, type IaAB diamond at its New York laboratory. It matched the stone to a previously submitted 11.07-carat rough, according to an article in the summer issue of the institute’s quarterly journal, Gems & Gemology.
The diamond exhibited an unusual absorption band at 525 nanometers and three additional features at 600, 608 and 618 nanometers, distinguishing it from the typical spectral pattern associated with pink coloration. The examination also identified an N3 center at 415 nanometers, a defect consisting of three nitrogen atoms and a vacancy in the diamond’s crystal structure.
Microscopic examination revealed needle-like inclusions forming a cloud, transparent internal graining, and color zoning resulting from plastic deformation of the diamond’s crystal structure. Under cross-polarized light, the stone displayed mottled strain patterns with high interference colors, indicating internal stress and structural distortion during its natural formation. DiamondView imaging revealed crystal growth patterns and blue fluorescence associated with the N3 center. Gemological testing confirmed the diamond’s natural origin and color, with no evidence of coating, treatment or laboratory growth, the article explained.
The origin of the 525-nanometer absorption band and the three peaks remains unknown. A previous study of a pink diamond with a 525-nanometer absorption band found high concentrations of nickel- and hydrogen-related defects. However, the lab detected no such impurities in this stone, suggesting that the absorption pattern may not have been documented before. The 525-nanometer band and the three peaks likely point to a previously unseen unusual, naturally occurring color center.
The findings highlight the complexity of natural-diamond coloration and the need for further research, the GIA concluded.
Image: The pinkish-brown diamond in its polished and rough forms. (Gemological Institute of America)
