Black diamond, not a ski slope

 

The strange 500+ carat black diamond named the "Enigma" was recently put on sale -- and sold for about $4.3 million dollars. 

Definitely a collector's item.  

The huge black diamond just sold for $4.3 million.  No one knows where it came from. (National Geographic)

"As diamonds crystallize in the immense pressures deep within Earth, they occasionally encapsulate minerals from the planet's mantle, such as deep red garnet or green olivine. But these minerals are absent in carbonados. Instead, geologists have found an exotic array of metals, such as the titanium nitride mineral osbornite, which is most commonly found in meteorites."

The article also note that this kind of diamond, called "carbonado", is harder than regular diamonds and they are used in industrial drillbits.

But this one won't be.