There are some well-known and prominent diamond dealers, manufacturers, and retailers operating in the U.S. diamond market.

Here are a few of the big ones…

1. De Beers –> De Beers, a global diamond mining and trading company, has a significant presence in the United States. While not primarily a U.S.-based company, De Beers is a major player in the international diamond industry and has operations in the U.S.
2. Alrosa –> Alrosa is another major global diamond producer and supplier with a presence in the United States. The company is based in Russia but exports diamonds worldwide, including to the U.S.
3. Signet Jewelers –> Signet Jewelers is one of the largest jewelry retailers in the United States, operating well-known brands such as Kay Jewelers, Zales, and Jared. They have a substantial retail footprint across the country.
4. Blue Nile –> Blue Nile is a prominent online diamond and jewelry retailer based in the United States. They offer a wide selection of diamonds and engagement rings to consumers.
5. James Allen –> James Allen is another notable online diamond and jewelry retailer headquartered in the U.S. They are known for their high-resolution 360-degree diamond viewing technology.
6. Rio Tinto –>While not based in the U.S., Rio Tinto is a global mining company with diamond operations in several countries, including Canada, which supplies diamonds to the U.S. market.

Please note that the landscape of the diamond industry can change, and the rankings of companies may evolve over time. To obtain the most current information on the largest diamond dealers in the U.S., you may want to refer to industry reports, market analyses, and financial data from reliable sources within the diamond industry.