The stone, found at Alrosa’s Nyurba site in Siberia, weighs just 0.62 carats, with an internal cavity of 6 cubic millimeters holding another crystal of just 0.02 carats, the miner said in a statement. It’s the first diamond of that nature to ever be found and may be more than 800 million years old, Alrosa said, citing scientists.

Diamond within a diamond. Source: Alrosa PJSC

The Russian gem producer has also made other rare finds in recent years. In August, it said it plans to sell a 14.83-carat pink gem, named The Spirit of the Rose, that is expected to fetch one of the highest prices ever for a diamond.

X-ray of the diamond within a larger diamond.Source: Alrosa PJSC

Alrosa plans to send the Matryoshka diamond to the Gemological Institute of America for further analysis, a spokesman said. There are no details yet on how much the gem may be worth.