The Cullinan diamonds are the nine principal polished stones cut from the Cullinan rough crystal, a 3,106.75-carat gem-quality diamond recovered in January 1905 from the Premier Mine near Pretoria, in what was then the Transvaal Colony of South Africa. Numbered I through IX and collectively styled the Stars of Africa, they represent the most celebrated single yield in the history of diamond cutting. The two largest — Cullinan I at 530.20 carats and Cullinan II at 317.40 carats — remain the largest and second-largest colourless faceted diamonds in the world, both now set permanently in the British Crown Jewels. All nine stones are classified as Type IIa, the chemically purest category of diamond, and all are of exceptional clarity. Their combined weight, the extraordinary provenance of the rough, and the technical audacity of the cleaving operation place the Cullinan diamonds in a category entirely their own within the gemmological record.

Discovery and the Premier Mine

The Premier Mine — now known as the Cullinan Mine and still in operation — was opened in 1902 by Thomas Cullinan, a Johannesburg building contractor who had purchased the farm Elandsfontein after recognising its diamond potential. The mine sits within the Cullinan kimberlite pipe, one of the largest kimberlite intrusions in southern Africa, and has historically produced an exceptional proportion of large, high-quality Type IIa crystals. This geological character is not coincidental: the Cullinan pipe taps a deep mantle source particularly rich in the conditions that produce nitrogen-free, inclusion-poor diamonds.

On 26 January 1905, Frederick Wells, the mine's surface manager, noticed a glint in the wall of the open pit some 5.5 metres below the surface. The crystal he extracted weighed 3,106.75 carats — approximately 621 grams — and measured roughly 10 cm × 6.5 cm × 5 cm. It was of exceptional transparency and pale blue-white colour. One face of the crystal was a natural cleavage plane, suggesting that the stone was itself a fragment of a much larger original crystal, though no matching piece has ever been conclusively identified. The Transvaal government purchased the rough in 1907 for £150,000 and presented it to King Edward VII as a gesture of loyalty following the end of the Boer War.

The Asscher Cleaving Operation

The task of dividing the Cullinan was entrusted to I.J. Asscher & Co. of Amsterdam, then the world's foremost diamond-cutting house, whose founder Joseph Asscher had cleaved the Excelsior diamond in 1903. The commission was one of extraordinary technical and psychological pressure. Joseph Asscher and his team studied the rough for several months, mapping its internal grain, natural cleavage planes, and inclusions before committing to a plan.

On 10 February 1908, Asscher made the first cleave. He inserted a specially made steel blade into a prepared groove and struck it with a mallet. The blade broke. On the second attempt, the stone divided cleanly along the intended plane. Contrary to the popular account that Asscher fainted from relief, contemporary records suggest he was composed, though the emotional weight of the operation was considerable. The initial cleave divided the rough into two principal pieces; subsequent sawing and cleaving operations over the following months produced the nine major gems, 96 smaller brilliants totalling approximately 7.55 carats, and 9.50 carats of polished fragments — a total polished yield of roughly 35 per cent by weight, which is consistent with the yield expected from a large, high-quality octahedral crystal with one natural cleavage face.

The Nine Principal Stones

The nine Cullinan diamonds are distinguished by their individual cutting styles, weights, and current settings within the British Royal Collection:

• Cullinan I (530.20 ct) — A pear-shaped brilliant of 74 facets, also called the Great Star of Africa. It is set in the head of the Sovereign's Sceptre with Cross, part of the Crown Jewels held in the Tower of London. It is the largest colourless faceted diamond in the world.
• Cullinan II (317.40 ct) — A cushion-shaped brilliant of 66 facets, also called the Second Star of Africa. It is set in the front band of the Imperial State Crown. It is the second-largest colourless faceted diamond in the world.
• Cullinan III (94.40 ct) — A pear-shaped brilliant. Together with Cullinan IV, it forms part of a brooch that Queen Mary had made in 1911; the pair are sometimes referred to as Granny's Chips, a phrase attributed to Queen Elizabeth II.
• Cullinan IV (63.60 ct) — A cushion-shaped brilliant. Mounted with Cullinan III in the brooch described above; the two stones can also be worn separately.
• Cullinan V (18.80 ct) — A heart-shaped brilliant. Set in a brooch with a platinum surround, part of Queen Mary's collection and subsequently inherited by the Royal Family.
• Cullinan VI (11.50 ct) — A marquise brilliant. Set in a brooch given by King Edward VII to Queen Alexandra; later acquired by Queen Mary and incorporated into the Royal Collection.
• Cullinan VII (8.80 ct) — A marquise brilliant. Suspended from a brooch containing Cullinan VIII.
• Cullinan VIII (6.80 ct) — An oblong brilliant. Set in a brooch, often worn with Cullinan VII as a pendant drop.
• Cullinan IX (4.39 ct) — A pear-shaped brilliant, the smallest of the nine. Set in a ring.

All nine stones remain in the possession of the British Royal Family as part of the Royal Collection, and none has been offered for public sale. Cullinan I and II are on permanent public display in the Jewel House at the Tower of London as components of the working regalia.

Gemmological Character: Type IIa and Exceptional Clarity

All nine Cullinan diamonds are classified as Type IIa — the category defined by the near-total absence of nitrogen impurities within the crystal lattice. Type IIa diamonds represent a small minority of all gem diamonds (estimates from the Gemological Institute of America place the proportion at roughly 1 to 2 per cent of gem-quality production), and the category is associated with the highest levels of optical transparency, since nitrogen clusters are the principal cause of yellow or brown bodycolour in most diamonds. The Cullinan rough's pale blue-white appearance, and the colourless to faintly blue-white character of the polished stones, is a direct consequence of this chemical purity.

The clarity of the principal Cullinan stones is exceptional by any standard. The rough itself was described by contemporary observers as remarkably free of inclusions, and the polished gems are generally reported as internally flawless or very nearly so. No independent laboratory grading reports for the Cullinan stones are in the public domain — they have never been submitted to GIA or any other commercial laboratory — but the consensus of gemmological literature is consistent on this point.

The faint blue-white fluorescence sometimes attributed to the Cullinan stones under ultraviolet light is consistent with the behaviour of many Type IIa diamonds, which can exhibit blue or blue-white fluorescence due to structural defects rather than nitrogen-related centres. This characteristic contributes to the stones' luminous appearance in daylight.

The Cullinan Mine's Continued Legacy

The Premier Mine, renamed the Cullinan Mine in 2003, has continued to yield exceptional Type IIa diamonds. Notable subsequent recoveries include the 273.85-carat Premier Rose (1978), the 599-carat Lesedi La Rona was recovered from a different mine (Karowe, Botswana), but the Cullinan pipe produced the 507-carat Cullinan Heritage in 2009 and the 299.30-carat Cullinan Dream rough in 2014. The mine is currently operated by Petra Diamonds. Its consistent production of large, high-quality Type IIa crystals is a function of the pipe's deep mantle source and the particular geochemical environment of its formation.

The geological relationship between the Premier/Cullinan pipe and the extraordinary size of the original Cullinan rough has been a subject of ongoing scientific interest. Some researchers have proposed that the 3,106-carat crystal formed at exceptional depth — possibly in excess of 400 kilometres — under conditions of unusually low nitrogen fugacity, which would account for both its size and its Type IIa character. The natural cleavage face on the original rough remains a point of discussion: if the Cullinan was indeed a fragment of a larger crystal, the complete original would have been of almost incomprehensible size.

Historical and Cultural Significance

The gift of the Cullinan rough to King Edward VII was a politically charged act. The Transvaal had been a Boer republic until its defeat in the South African War (1899–1902), and the presentation of the world's largest known diamond to the British Crown was intended to signal reconciliation and loyalty under the new constitutional arrangement. The Transvaal parliament voted 42 to 19 in favour of the gift, and the decision was not without controversy among Boer members who regarded it as a capitulation. The stone was transported to Britain under elaborate security arrangements — a decoy parcel was sent by sea while the actual rough travelled by post in a plain box, a story that has since acquired the character of legend but is supported by contemporary accounts.

The incorporation of Cullinan I and II into the working regalia of the British monarchy — instruments used at coronations and state occasions — means that these stones have a living ceremonial function that distinguishes them from most famous diamonds, which are museum objects or private possessions. Cullinan I was worn by Queen Elizabeth II at the State Opening of Parliament throughout her reign, either in the Sceptre or, on occasion, as a brooch in combination with Cullinan II. King Charles III wore the Imperial State Crown containing Cullinan II at his coronation in May 2023.

Questions of repatriation have been raised periodically, particularly in the context of broader debates about colonial-era acquisitions. The South African government has at various times been asked to comment on the Cullinan diamonds' status, and the issue remains a point of cultural and political discussion, though no formal repatriation claim has been lodged as of the time of writing.

In the Trade and Gemmological Literature

Because the Cullinan diamonds have never entered the commercial market, they have no auction record and no published laboratory reports. Their significance to the trade is therefore primarily historical and educational: they establish the upper boundary of what is possible in terms of the size of a faceted diamond, and they serve as the defining reference for Type IIa quality at the largest scale. The Cullinan I's 530.20-carat weight remained the record for the world's largest faceted diamond for over a century; it was surpassed in 2019 by the Golden Jubilee Diamond (545.67 carats, fancy yellow-brown), which was cut from a rough recovered from the same Premier Mine in 1985 — a fact that underscores the singular geological character of the Cullinan pipe.

The cutting of the Cullinan rough by Joseph Asscher is cited in gemmological education as a landmark in the history of diamond cleaving, both for the technical analysis required and for the scale of the operation. The Asscher firm — now the Royal Asscher Diamond Company — continues to reference the commission as a defining moment in its history. The 96 smaller brilliants produced alongside the nine principal stones were retained by the Asscher firm as partial payment for their work, a detail that speaks to the negotiated nature of the commission and the difficulty of placing a monetary value on the labour involved.

Further Reading

• GIA — The Cullinan Diamond
• GIA Gems & Gemology — Type IIa Diamonds
• Royal Collection Trust — The Crown Jewels