The Gemological Institute of America (GIA) has identified an atypical colour centre in a 5.22-carat natural pinkish-brown diamond, following an analysis at its New York laboratory. The findings were published in the summer 2026 issue of the institute’s journal, Gems & Gemology.

The pear brilliant, classified as a type IaAB diamond and graded very light pinkish brown, was matched to an 11.07-carat rough stone previously submitted to GIA. The laboratory established the match using ultraviolet-visible and mid-infrared spectral analysis.

The polished diamond displayed an unusual absorption band at 525 nanometres, alongside three additional spectral features at 600, 608 and 618 nanometres. These differ from the typical absorption pattern associated with pink coloration in natural diamonds. The analysis also detected an N3 centre at 415 nanometres, a structural defect involving three nitrogen atoms and a vacancy.

Microscopic examination revealed needle-like inclusions, internal graining and colour zoning associated with deformation of the crystal structure. DiamondView imaging showed crystal growth patterns and blue fluorescence. Gemological testing confirmed the diamond’s natural origin and colour, with no evidence of coating, treatment or laboratory growth.

The origin of the 525-nanometre absorption band and the three additional features remains unknown. Although an earlier study associated a similar absorption band with nickel- and hydrogen-related defects, GIA detected neither in this stone. The institute said the findings may indicate a previously undocumented natural colour centre.

The study highlights the complexity of colour formation in natural diamonds and the need for further research into the defects responsible for their optical properties.