I thought that could only happen in the extreme conditions of a star. I know our own sun, when it collapses into a white dwarf, will have a pure carbon interior and be a giant diamond too. But it'll be black on the surface (after it cools down) and you'd never be able to see it.
Anyone else love "How The Universe Works"? It has the best CGI I've ever seen for a space show.
Call it "Planet DeBeers"!
You need to read "The Elegant Universe" , easy read by physicist Brian G. You'll need tuna sandwiches to keep your brain going. As you think, the brain starts "grooves" to apply surface area. Once you read this, you will spit on psychics & other charlatans who don't have the BALLS to bother getting through a read like this. It almost explains why people see ghosts & a host of other paranormal phenom. You'll never be the same & need no knowledge of physics to read it. The number 9 will amaze you.
Considering the cost to get there and bring them back, the diamonds would be more expensive than earth diamonds.