The Gemological Institute of America (GIA) has recently examined two diamonds featuring rare star-shaped inclusions.
Weighing 8.14 and 8.57 carats respectively, these diamonds, referred to as asteriated or “star” diamonds, were highlighted in the summer 2024 edition of Gems & Gemology.
The discovery is notable for both the size of the stones and their preserved natural forms, providing insights into the geological history of diamond formation.
Asteriated Diamonds: Composition and Features
Both diamonds displayed light brown cloud inclusions, a phenomenon caused by high concentrations of hydrogen and nickel during the diamond growth process. Inclusions of this type, which may also contain graphite, are rare and contribute to the unique character of these gems. According to the GIA, while asteriated diamonds occasionally pass through their labs, these two specimens stand out due to their considerable size and the clarity of their preserved forms.
The 8.14-carat diamond presented a blend of natural and processed features. One side retained its rough shape, showing brown radiation stains, which GIA linked to natural alpha irradiation followed by annealing deep within the Earth’s crust. The other side was sliced, revealing the star-shaped inclusion pattern underneath.
The 8.57-carat diamond, polished with bruted edges, also displayed the distinctive star-shaped inclusions. Like the 8.14-carat stone, it underwent resorption, a process where natural fluids or magma partially dissolve the diamond, resulting in a more rounded form while maintaining significant aspects of its original structure.
Scientific Examination
The GIA employed advanced techniques to analyse the diamonds’ inclusion patterns and growth history. Using bulk Fourier-transform infrared spectroscopy, the lab detected high concentrations of hydrogen within both stones. Photoluminescence mapping of the 8.14-carat diamond revealed nickel-related defects concentrated within the cloud inclusion sector, while X-ray computed microtomography provided 3-D reconstructions that highlighted the star-shaped growth sectors. These areas were found to absorb X-rays more strongly than the surrounding material, likely due to the higher atomic number of the combined signal from the diamond and inclusions.
Additionally, both diamonds exhibited green fluorescence when subjected to long-wave ultraviolet (UV) light, a trait consistent with previously studied asteriated diamonds.
