Two large natural diamonds bearing star-like cloud inclusions were recently sent to the Carlsbad office of the Gemological Institute of America (GIA) for scientific examination. 

Though the GIA occasionally sees these types of stones, known as “asteriated” or “star” diamonds, these were particularly notable due to their size as well as their preserved natural forms, the organization said in its most recent issue of the Gems & Gemology periodical, issued last week. The stones, which weigh 8.14 and 8.57 carats, got their light-brown cloud inclusions from high concentrations of hydrogen and nickel during their growth period. They are also thought to contain graphite, the GIA noted. 

The 8.14-carat diamond was resorbed and maintained most of its rough form on one side. It was sliced to reveal the underlying inclusion pattern on the other side. The preserved rough surfaces also displayed brown radiation stains, which indicated it had natural alpha irradiation followed by annealing in the earth. Meanwhile, the 8.57-carat stone was polished, with bruted edges.  

Both stones fluoresced green when subjected to long-wave UV, a trait common in asteriated diamonds, the GIA noted. The institute used scientific procedures, including X-ray computed microtomography and Fourier-transform infrared spectroscopy, during the examination process.

Image: The two diamonds with star-like inclusions. (Gemological Institute of America)