An exceptional “diamond in a diamond” found this year at Alrosa’s Yakutia mine has made it to the Russian miner’s repository of rare specimens that are not for sale.

The Matryoshka diamond, named after a traditional Russian Matryoshka doll, joins a collection of rough diamonds – one shaped like a skull and the other a football – that the company has mined in recent years. 

The Matryoshka diamond, believed to be the first of its kind in the history of diamond mining, could be more than 800 million years old. Despite its complex structure, it weighs only 0.62 carats (0.124 grams) and has maximum dimensions of 4.8mm by 4.9mm by 2.8mm. The internal cavity volume is 6 cubic mm and the internal crystal volume is 1.6 cubic mm with an estimated weight of 0.02 carats (0.004 grams). The inner diamond has a tabular shape and dimensions of 1.9mm by 2.1mm by 0.6mm.

Specialists at the Yakutsk Diamond Trade Enterprise discovered the unusual diamond during the sorting process and handed it over to the Research and Development Geological Enterprise of Alrosa. It was studied using several methods, including Raman and infrared spectroscopies, as well as X-ray microtomography. Based on the results, the scientists hypothesised about how the crystal was formed. According to them, there was an internal diamond at first, and the external one was formed during the subsequent stages of growth.

They further commented that some parts of a mineral are usually replaced by others without a cavity. On the other hand, regular diamonds may have small gas-liquid inclusions. However, such large cavities have never been found in crystals before, experts said.