113-19 525 nm Absorption Band: Evidence of an Atypical Pink Color Center in Natural Diamond

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones (Posters)

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Abstract:

The GIA New York laboratory examined a natural rough type IaAB diamond (11.07 ct) and the same stone fashioned into a very light pinkish brown pear brilliant (5.22 ct). Spectroscopic analysis revealed identical UV-visible and mid-infrared spectra. The UV-visible displayed a rare ~525 nm absorption band and a triplet feature at ~600, ~608 and ~618 nm, which are distinct from the typical broad ~550 nm absorption band. The ~550 nm band is characteristic for causing pink coloration due to plastic deformation in the crystal lattice. There is a prior study of a pink diamond exhibiting a ~525 nm absorption band with high concentrations of Ni- and H-related defects. However, no nickel or hydrogen defects were detected in this pinkish brown diamond, suggesting a different naturally occurring ~525 nm color center.

Microscopy identified natural features including a cloud of needle-like inclusions, transparent internal graining, and color zoning representative of type IaAB diamonds. There was no indication of treatment, surface coating, or laboratory growth. Strain patterns observed under cross-polarized light with high interference colors showed internal stresses and distortions during formation. Fluorescence imaging using the DiamondView™ exhibited natural diamond growth patterns and characteristic blue fluorescence associated with this diamond type. The blue emission results from the presence of the N3 center in the crystal lattice.

It is known that the N3 contributes to the overall body color, and the NV color center creates pink and brown hues. The cause of the ~525 nm absorption band and the triplet feature at ~600, ~608 and ~618 nm remains unknown but is most likely an atypical naturally occurring color center in natural diamond from deeper crystal lattice defects and deformation, potentially separate from the typical broad ~550 nm absorption band. These findings highlight the complexity of color origin in diamonds and the need for ongoing research into naturally occurring color centers.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9205

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