The Cullinan Diamond: The Largest Gem-Quality Rough

## Discovery On January 26, 1905, Frederick Wells, the surface manager of the Premier Mine near Pretoria, South Africa, spotted a glint of light in the mine wall during a routine inspection. He extracted what turned out to be the largest gem-quality diamond ever found: a crystal weighing 3,106.75 carats (621.35 grams) — roughly the size of a man's fist. The diamond was named the Cullinan after Sir Thomas Cullinan, the mine's chairman. The crystal was a fragment of what must have been an even larger original — one cleavage face was flat and smooth, indicating the Cullinan was a broken piece. The rest of the original crystal has never been found. The Cullinan was a Type IIa diamond — chemically extremely pure, with virtually no nitrogen impurities. Type IIa diamonds are among the rarest (only about 1-2% of all diamonds) and the most optically transparent. ## Purchase and Gift The Transvaal Colony government purchased the Cullinan for 150,000 pounds sterling and presented it to King Edward VII of the United Kingdom as a 66th birthday gift on November 9, 1907. The gesture was politically motivated — it was intended to repair relations between Britain and the Boer population of South Africa after the devastating Boer War (1899-1902). The decision to give such a valuable stone to a foreign monarch was controversial in South Africa. Some saw it as a generous diplomatic gesture; others viewed it as surrendering a national treasure to the colonial power. ## The Cutting: Asscher of Amsterdam Edward VII entrusted the cutting to Joseph Asscher of I.J. Asscher & Co. in Amsterdam, the most famous diamond cutting firm in the world. The Asscher family had previously cut the Excelsior diamond (995 carats) and had an unmatched reputation for handling exceptional stones. The task was formidable. A single error in analyzing the crystal's internal structure could have shattered the stone into worthless fragments. Asscher studied the Cullinan for months, examining it under magnification, analyzing its cleavage planes, and planning the cutting sequence. On February 10, 1908, Asscher placed a steel blade in a groove he had carefully cut into the diamond and struck it with a heavy rod. According to legend, the blade broke on the first attempt, and Asscher fainted after the second successful strike. A more prosaic account (from the Asscher company) states that the cleaving went smoothly and Asscher celebrated with a glass of champagne. The Cullinan was ultimately cleaved and cut into nine major stones, 96 small brilliants, and some unpolished fragments. ## The Nine Major Stones ### Cullinan I (Great Star of Africa) **Weight**: 530.20 carats — the largest clear-cut diamond in the world (until the 2017 cutting of the Lesedi La Rona) **Cut**: Pear-shaped brilliant with 74 facets **Setting**: The head of the Sovereign's Sceptre with Cross, part of the British Crown Jewels **Significance**: This stone alone would rank among the world's greatest diamonds. Its pear shape was chosen to maximize yield from the largest section of the original crystal. ### Cullinan II (Second Star of Africa) **Weight**: 317.40 carats **Cut**: Cushion-shaped brilliant with 66 facets **Setting**: The front of the Imperial State Crown, directly below the Black Prince's Ruby **Significance**: The second-largest stone from the Cullinan, it is one of the most prominently displayed diamonds in the Crown Jewels. ### Cullinan III **Weight**: 94.40 carats **Cut**: Pear-shaped brilliant **Setting**: The top of Queen Mary's Crown; can be worn as a pendant with Cullinan IV ### Cullinan IV **Weight**: 63.60 carats **Cut**: Square-cushion brilliant **Setting**: The band of Queen Mary's Crown; can be worn as a brooch combined with Cullinan III ### Cullinan V **Weight**: 18.80 carats **Cut**: Heart-shaped brilliant **Setting**: Brooch, set in a platinum mounting surrounded by smaller diamonds ### Cullinan VI **Weight**: 11.50 carats **Cut**: Marquise **Setting**: Pendant on a diamond and platinum necklace ### Cullinan VII **Weight**: 8.80 carats **Cut**: Marquise **Setting**: Pendant on a platinum and diamond chain ### Cullinan VIII **Weight**: 6.80 carats **Cut**: Brilliant **Setting**: Mounted as a brooch ### Cullinan IX **Weight**: 4.39 carats **Cut**: Pear-shaped brilliant **Setting**: Ring in platinum with a prong mount ## The Cullinan's Gemological Importance Beyond its size, the Cullinan is scientifically significant: **Type IIa classification**: The Cullinan's extreme purity (virtually no nitrogen) makes it a Type IIa diamond. Type IIa diamonds form deeper in the Earth's mantle than typical (Type Ia) diamonds, under conditions of extreme pressure and temperature. They are believed to form at depths of 400-700 kilometers — far deeper than the 150-200 km typical of most diamonds. **"CLIPPIR" diamonds**: Recent research has classified the Cullinan as a member of a group called CLIPPIR (Cullinan-Like Large Inclusion-Poor, Relatively Pure) diamonds. These large, high-quality Type IIa diamonds share specific characteristics suggesting a common deep-mantle origin. They may form in metallic liquid iron-nickel-carbon-sulfur melts in the lower mantle. **Cleavage fragment**: The flat cleavage face on the original rough indicates it was a fragment of a much larger crystal. Estimates suggest the complete original crystal could have weighed over 6,000 carats. This remains the largest known diamond crystal in history, even though only half of it was ever found. ## Legacy The nine Cullinan diamonds remain in the British Crown Jewels, displayed in the Tower of London. They are among the most visited gemstones in the world. Like the Koh-i-Noor, the Cullinan diamonds have been the subject of repatriation discussions — South African voices have periodically called for the stones' return, arguing they are part of South Africa's national heritage. The Premier Mine (renamed the Cullinan Mine in 2003) continues to operate and has produced other notable diamonds, including the 507-carat Cullinan Heritage and the 353-carat unnamed blue diamond. But nothing has approached the scale of the original 1905 discovery.