They break the unspoken norm of the colorless crystal-clear stone that every girl dreams of, although definitely in a good way. How Rare are They? Original black diamonds are exceedingly rare, and can cost you a small fortune if you decide to buy one. You will end up paying somewhere between 3k and 5k for a carat, which is ten times what a treated black diamonds would cost you. South America has the biggest concentration of black diamonds in the world, with Brazil being the largest miner. In Fine Jewelry Black diamonds make wonderful additions to fine jewelry, because they are versatile enough to adapt beautifully to a variety of design concepts. They usually feature in the most exclusive creations, and play well in dark and enigmatic settings. As for the metals they match, take your pick. It does bear mentioning that rose gold and yellow gold are the best metal choice for a black diamond ring, whether it is an engagement ring you are considering or a wedding ring.