African rough diamonds ?

If you were to rank the producers of diamonds in Africa from 1-100 then all the rest would be 1 and Oppenheimer/De Beers 99.

They achieve this by keeping any new producers out of exploiting the African deposits :

 "Land-locking" is a longstanding tactic, where the applicant (for mineral rights) will apply for rights with the intention of never exploiting them, the aim,  just to keep as many newcomers out as possible- except heavy weights, American Mineral Fields, BHP and the like, and those "agents" of De Beers who have served them well.

And then imagine the advantage one has when the relevant African government officials from the top to the bottom are manipulated.  

cases to be presented soon - Tosscani, Skeleton coast, Namibia.