Given what I know about the process of diamond formation, it’s hard to understand how such a gem is possible.

“A unique 'gem inside a gem' diamond has been unearthed in Siberia.

The 800 million-year-old two-in-one jewel is said to be priceless and the only such discovery in the world.

The so-called 'Matryoshka' diamond is named because it resembles traditional Russian nesting dolls, one inside the other…”

https://mol.im/a/7540555