Barely large enough to qualify as a top-tier diamond mining company, most of their holdings are in the southern part of Africa, one of the world's richest areas of diamond production. Although Rockwell's holdings are insufficient to qualify it as one of the world's largest diamond companies, the company’s fame came from a high media profile after a private holdings group attempted a hostile takeover. Fortunately for those at Rockwell Diamonds, the attempt failed, allowing the company to remain among the top ten.

Having two headquarters located in Johannesburg, South Africa, and the other in London, England, Anglo American plc does more than produce diamonds. While they are among the world's largest diamond mining companies, they are also the world's single largest producer of another precious material: platinum. They also have interests in producing a number of other materials, including copper and gold. However, their diamond production remains among the highest on the planet, and they own several of the world's richest mines, primarily in southern Africa.

Based in England, Gem Diamonds operates worldwide, as any diamond company must be, to achieve enough holdings to make it onto this list. It is notable because only a year after its founding, it announced the finding of an unusually large diamond, at 600 carats, making one of the largest diamonds found in the last 25 years. This put the company on the map and has grown exponentially ever since. It currently maintains mines and operates labs in a number of different countries, including Angola, Australia, Botswana, Indonesia, Lesotho, and the Democratic Republic of the Congo.

Originally focused almost entirely on exploration (finding new sources of diamonds), this company has, in recent years, shifted its focus towards the production of diamonds (the mining and cutting of rough diamonds). They currently own shares in eight diamond mines, including 5 of the world's largest and most productive mines. They still explore Botswana, though that does not remain their primary focus. Most of their mines are also in the rich region of southern Africa; they have recently expressed interest in expanding their operations elsewhere.

This Canadian diamond company struggled, losing 26% of its value in recent years. But that fortune changed overnight recently when a mine owned by the company uncovered the largest diamond found in over a century. Weighing in 1,111 carats raw, this gem-quality stone added nearly $150 million to the company's value as their stock skyrocketed. The diamond is so large that it did not fit into the scanners owned by the company, and it had to be shipped to a world diamond market located in Europe to be properly assessed. Thus, little is still known about this already-famous diamond.

Based in Toronto, Canada, Dominion Diamond Corporation reported $700 million in revenue in 2012. They were originally known as the Harry Winston Diamond Corporation. Today, they operate mines in Canada; the most well-known is the Diavik diamond mine in Lac de Gras. The Rio Tinto Group, another company on this list, helps to operate that mine with Dominion Diamonds, although Dominion still owns the rights and property of the entire mine. The company was founded on mining the Diavik mine and was established in 1994 when the mine was discovered to produce diamonds.

One of the few companies with headquarters outside the Western world, located in Botswana, the company operates four mines in the country. These mines are the Orapa, Letlhakane, Jwaneng, and Damtshaa mines. Unlike other mining companies, which frequently are targets of calls from human rights activists worried about 'blood diamonds,' this company has proven to be a powerhouse in the growth of the Botswanian economy. Botswana was once one of the poorest nations on earth; today, while it is far from the richest, it has one of the world's fastest-growing economies. Debswana is a major part of that growth.

With over $4 billion in revenues, the top companies on this list include Rio-Tinto Diamonds. Rio-Tinto is unlike many other diamond companies; it is a mine-to-market company, meaning that a diamond can go from sitting in the ground to sitting in a jeweler's display case, all under the supervision of a single company. They operate on five of the seven continents. They own three mines, including one in Australia, known as the world's foremost producer of pink diamonds.

If De Beers is the household name for diamond companies, ALROSA is its Russian counterpart. They reported $4.4 billion in revenues in 2012. Most of their success in becoming the world's largest diamond company comes from discovering a single mine in Russia, to which ALROSA claims full ownership. That mine alone is thought to contain almost $4 billion in diamonds, and ALROSA has the exclusive right to mine it. Their mines are in Russia, and most of their mining operations occur in Siberia's frozen steppes.

This is the giant, the household name, the standard against which all other diamond manufacturers are measured. Reporting $6.1 billion in revenues in 2012, De Beers has been around for a century and a quarter. As many critics claim, the company was originally founded with the intention to control the world diamond supply so that the company is the owner of the diamonds rather than market forces. Eventually, the company decided on the prices of the diamonds themselves. Thus, they were called a 'diamond cartel,' and those accusations have followed it to the present day. However, in recent years, it has come to light that De Beers does not have the control over the world's resources they were thought to have.