The Cullinan Diamond

Diamonds, more than any other gemstone, are steeped in legend and lore. Some are famous for their history, some for an exceptionally rare color, and some for their size.

The Cullinan Diamond, discovered more than 100 years ago, is one such diamond.


On January 26, 1905, the largest gem-quality diamond ever found was discovered at the Premier mine in South Africa. It was named for the mine’s owner, Thomas Cullinan.

The fist-sized rough stone weighed 3,106 carats (1.37 pounds), and was mined at a depth of only 18 feet, although its origins were likely to have been more than 200 miles below the earth’s surface (a bit more on that later).

As amazing as a diamond of this size is, some experts believe it was originally part of an even larger stone and that it had sheared off at some point in the past, a theory arising from the fact that the stone had one flat side.

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Frederick Wells, manager of the Premier Mine, with the 1.37 pound rough diamond. photo: Getty

The rough stone was put up for sale, but it took two years before it was purchased by the Transvaal Colony government (the region which is now Pretoria, South Africa) to give to King Edward VII of the United Kingdom.

Transporting the Cullinan

Even without the scourge of modern-day social media, the fact that the incredibly rare and valuable gem was being transported from South Africa to England could not have been kept secret. Armed detectives took the stone to Cape Town, where it was locked in a guarded safe on a steamship to London. Or so everyone was led to believe. The package contained a fake, and the real gem was sent to London in a plain box via ordinary registered post.

Cutting the Cullinan

Asscher Brothers of Amsterdam was chosen to cut and polish the Cullinan. One of the brothers, Abraham, picked up the real gem in London and traveled back to Amersterdam with it in his coat pocket. Meanwhile, another anti-theft diversionary tactic was being used. Publicly, the Royal Navy was given the responsibility for transporting the “gem” across the North Sea. Not even the captain knew his package was empty.

In Amsterdam, Joseph Asscher spent weeks studying the diamond. An incision was made preparatory to cleaving the diamond. This step alone took four days. Then, on the first attempt to cleave the diamond, the steel knife fitted into the incision broke. But on the second attempt it split cleanly.

Joseph Asscher, striking the blow the cleave the rough diamond. photo: Wikimedia

Over a period of eight months the diamond was split and cut into 9 major stones and 96 minor ones. Three cutters worked 14 hours a day during this time to achieve this.

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The nine major stones cut from the Cullinan. photo: Wikimedia

The two largest cut diamonds are the Cullinan I (aka Great Star of Africa, 530 carats) and Cullinan II (aka Second Star of Africa, 317 carats). These were returned to King Edward VII and became part of the British Crown Jewels. The remaining stones were kept by the  Asschers as payment for their services.

Mysterious Origin of Really Big Diamonds

Most diamonds are formed 90 to 140 miles beneath the earth’s surface. But a geologist named Evan Smith, who is a Post Doctoral Fellowship Researcher at GIA (the Gemological Institute of America), has studied exceptionally large diamonds such as the Cullinan and discovered that they have some unusual characteristics.

He has found that they have inclusions which are highly magnetic. This, along with other research, led him to conclude that unusually large diamonds are formed between 220 and 460 miles below the earth’s surface — 3 or 4 times deeper than all other diamonds.

Mining Diamonds

Diamonds, whether they originate 100 or 400 miles deep, are brought to the earth’s surface in the same way: volcanic eruptions. These eruptions form what are known as kimberlite pipes, some of which have diamond-rich deposits.

While kimberlite pipes are primary sources for diamonds, the gems are also found in what is known as alluvial, or secondary, deposits. In such cases the diamonds were separated from the kimberlite pipe either by the explosive force of the eruption which formed the pipe, or were washed away after millions of years of erosion. The oldest recorded source of diamonds (dating to before 500 BC) is India, and these were all alluvial deposits. No one has ever discovered the original kimberlite source!

Thanks for reading!

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