Blood Diamonds are diamonds from war torn africa. People are basically put into slavery and forced to pick out diamonds. Meanwhile, the money of these diamonds go into the warlords hands to fund their civil wars so that they can mass murder villages and put the few surviving people into slave camps.
And all the while, diamonds companies like debeers take these diamonds and collect them. So let's say someone tries to sell a pink diamond. If debeers doesn't want you to buy that kind of diamond from the other company, they flood the market with that type of diamond and drive the price down so they can make more money from their other diamonds.
Its all one big joke. If anyone from debeers steps foot into the US, they would be put in jail for their business practices, so they hide in europe.
So, if you want to buy a diamond to fund african civil wars and make europeans rich, by all means knock yourself out. Unlike gold, they arent worth a damn.