There are two aspects of moving diamonds from mine to dealer. The first is the fairly straightforward but important task of separating diamonds into gem-quality, near gem-quality, and industrial-grade diamonds. The second is the more intriguing aspect: the primary diamond marketing, which has been and still is largely controlled by De Beers Consolidated Mines, Ltd. through its majority control of the Central Selling Organization (CSO). The CSO sells a large percentage of mine production to diamond dealers; independent mines sell by closed bids and through private transactions.

Sorting small diamonds in a Botswanan operation.

Sorting occurs at every level of the market, from the mine to the jeweler. At the mine, the sorting depends on the sophistication of the operation and the size of production, but it is always based on grouping stones of like type. Diamonds are grouped into “sizes” — more than one carat; “smalls” — between 1 carat and 1/10th carat; and “sand,” — less than 1/10th carat, with some leeway for market pressures. Diamonds larger than about 15 carats are handled individually. Shape groups comprise “stones,” “shapes,” “cleavages,” “macles,” and “flats,” describing characteristics familiar to the market. The ultimate purpose of sorting is to estimate an asking price for the rough diamonds.