Cullinan III is a pear-shaped diamond of 94.4 carats, the third-largest of the nine principal stones cleaved and polished from the Cullinan rough by Joseph Asscher & Co. of Amsterdam in 1908. Together with its companion, Cullinan IV, it occupies a singular position in the history of royal jewellery: the two stones serve simultaneously as elements of the British Crown Jewels — set in Queen Mary's Crown — and as a detachable brooch of extraordinary magnificence that was worn with great frequency by both Queen Mary and, later, Queen Elizabeth II. As a Type IIa diamond of exceptional transparency and colourlessness, Cullinan III represents one of the finest examples of its mineralogical class in existence.

The Cullinan Rough: Context and Discovery

The story of Cullinan III begins on 26 January 1905, when Frederick Wells, surface manager of the Premier Mine (later renamed the Cullinan Mine) in Gauteng, South Africa, observed a glint of reflected light in the wall of the mine at a depth of approximately nine metres. The object he extracted proved to be a diamond crystal of 3,106.75 carats — roughly the size of a man's fist — making it the largest gem-quality rough diamond ever recorded. It was named after Sir Thomas Cullinan, the mine's owner.

The Transvaal government purchased the stone in 1907 for £150,000 and presented it to King Edward VII as a birthday gift, a gesture carrying considerable political significance in the years following the Second Boer War. The King entrusted the stone to the Amsterdam firm of Joseph Asscher & Co., then the world's foremost diamond-cleaving house, for division and polishing. The task of studying the rough and planning the cleave fell principally to Joseph Asscher himself, who is said to have spent months analysing the crystal's internal structure before making the first decisive blow in February 1908.

The rough yielded nine principal stones, designated Cullinan I through IX, along with ninety-six smaller brilliants and a quantity of polished fragments. The two largest stones — Cullinan I (530.2 carats, pear-shaped) and Cullinan II (317.4 carats, cushion-shaped) — were set in the British Crown Jewels as the Great Star of Africa and the Second Star of Africa respectively. Cullinan III, at 94.4 carats, ranked third in weight among the principal stones.

Mineralogical Character

Like all nine principal Cullinan stones, Cullinan III belongs to the Type IIa category of diamond — a classification defined by the near-total absence of nitrogen impurities within the crystal lattice. Type IIa diamonds are among the most chemically pure of all natural diamonds. This purity accounts for their exceptional optical transparency across a broad spectral range and, in the finest examples, for a colourlessness that appears almost luminous. The Cullinan rough itself has been described by gemmologists as exhibiting a faint bluish-white fluorescence and a body colour of the highest grade, characteristics that are preserved in the polished principal stones.

Cullinan III is fashioned as a pear brilliant — a modified round brilliant cut tapering to a single point at one end — a form that maximises the display of fire and brilliance while accommodating the elongated geometry of the cleaved section from which it was derived. At 94.4 carats, it remains one of the largest pear-shaped diamonds in the world. Its clarity, by all accounts consistent with the exceptional quality of the parent rough, places it at the pinnacle of the clarity scale, though no formal laboratory grading report in the contemporary sense has been publicly issued for a stone of its age and institutional ownership.

Cutting and Polishing by Joseph Asscher & Co.

The division of the Cullinan rough was among the most technically demanding operations in the history of diamond cutting. The crystal contained internal cleavage planes and inclusions that had to be mapped with precision before any blade was applied. Joseph Asscher's team worked under the supervision of the Assurance Committee appointed by the British government, and the entire process — from the first cleave to the final polishing of all principal stones — took approximately eight months.

The cleaving of a diamond exploits the mineral's perfect octahedral cleavage: a steel blade is seated in a pre-cut groove aligned with a cleavage plane, and a sharp blow causes the crystal to part cleanly along that plane. The first cleave of the Cullinan rough, dividing it into two primary sections, is one of the most celebrated moments in gem history. Subsequent cleaves and sawing operations divided the material further into the sections that would become the nine principal stones and the smaller brilliants.

Cullinan III was polished to its final pear-brilliant form in Amsterdam. The nine principal stones were returned to Britain, where Cullinan I and II were incorporated into existing Crown Jewels regalia. The remaining seven stones were retained by the Asscher firm as partial payment for their work, then purchased by the South African government, which presented them to Queen Mary in 1910.

Queen Mary's Crown and the Royal Setting

Queen Mary's Crown was made for the coronation of King George V in 1911 by the Crown Jewellers Garrard & Co. The crown's design incorporated a finial cross at its apex, and it is within this cross that Cullinan III is set, positioned as the central stone. Cullinan IV, a cushion-shaped diamond of 63.6 carats, is set in the band of the crown below the finial. The arrangement places the two largest of the seven stones gifted to Queen Mary in the most prominent positions of her coronation crown.

A distinctive feature of the crown's design — and a reflection of Queen Mary's practical approach to jewellery — is that both Cullinan III and Cullinan IV were made detachable from their settings. This allowed the two stones to be removed from the crown and worn together as a brooch, a configuration that became one of the most recognisable pieces of royal jewellery in the twentieth century. The brooch setting joins the pear-shaped Cullinan III above the cushion-shaped Cullinan IV, creating a pendant-like form of considerable visual weight and brilliance.

The Brooch: "Granny's Chips"

Queen Mary wore the Cullinan III and IV brooch with notable regularity throughout her life, and it became so closely associated with her that the two stones acquired an affectionate nickname within the royal family: Granny's Chips. The sobriquet, attributed to members of the family in reference to the stones' origin as chips from the great Cullinan rough, captures the intimacy with which the brooch was regarded despite — or perhaps because of — its extraordinary monetary and historical value.

Upon Queen Mary's death in 1953, the brooch passed to Queen Elizabeth II, who wore it frequently over the following seven decades, making it one of the most photographed pieces of jewellery in the world. The Queen was photographed wearing the brooch on state occasions, during Commonwealth tours, and in numerous formal portraits, ensuring that Cullinan III remained a living presence in public life rather than a static museum object. Following Queen Elizabeth II's death in September 2022, the brooch passed to Queen Camilla.

The Crown Jewels and Public Display

When not worn as a brooch, Cullinan III resides in its setting within Queen Mary's Crown, which is displayed in the Jewel House at the Tower of London as part of the British Crown Jewels. The crown is exhibited alongside the other principal regalia — including the Imperial State Crown containing Cullinan II — making the Tower of London one of the few places in the world where multiple stones from a single historic rough can be viewed in close proximity.

The display context places Cullinan III within a narrative of imperial history, colonial-era gem discovery, and the evolution of the British monarchy's material culture. For gemmologists and historians alike, the Crown Jewels collection offers a rare opportunity to observe Type IIa diamonds of this calibre in their historical settings, even if close examination is necessarily limited by the conditions of public display.

Valuation and Market Context

No formal public valuation of Cullinan III has been issued in the modern era, and the stone is not subject to commercial sale. Its value, were it ever to be assessed, would be determined by the intersection of several exceptional factors: its weight of 94.4 carats in a pear-brilliant cut, its Type IIa classification, its presumed D-colour or equivalent colourlessness, its extraordinary clarity, and — perhaps most significantly — its provenance as one of the nine principal stones from the Cullinan rough and a piece of documented royal history spanning more than a century.

For comparative context, large Type IIa pear-shaped diamonds of exceptional quality have achieved prices at auction in excess of one million US dollars per carat in recent years, though such benchmarks are imperfect guides to a stone of Cullinan III's unique historical status. The Cullinan I and II, set in working regalia, are considered effectively priceless and are not subject to insurance valuation in the conventional sense.

The broader Cullinan legacy continues to influence the market for large rough diamonds from the Cullinan Mine. The Cullinan Heritage, a 507.55-carat rough diamond recovered from the same mine in 2009, was sold to Chow Tai Fook for approximately 35.3 million US dollars, demonstrating the enduring premium commanded by stones from this exceptional kimberlite source.

Scientific Significance

Beyond their historical and aesthetic importance, the Cullinan stones hold scientific interest as examples of what researchers have termed CLIPPIR diamonds (Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed) — a category of exceptionally large, Type IIa diamonds that form at depths of 360 kilometres or more in the Earth's mantle, well below the lithospheric keel where most diamonds crystallise. Research published in the journal Science in 2016 by Smith et al. identified metallic iron–nickel inclusions in diamonds of this type, suggesting formation in a region of the mantle where iron exists in its metallic rather than oxidised state. While Cullinan III itself has not been subjected to destructive inclusion analysis, the broader CLIPPIR category to which it almost certainly belongs has transformed understanding of deep-mantle carbon cycling and the conditions under which the largest gem-quality diamonds originate.

The Nine Principal Cullinan Stones: A Summary

• Cullinan I — 530.2 carats, pear brilliant; set in the Sovereign's Sceptre with Cross.
• Cullinan II — 317.4 carats, cushion brilliant; set in the Imperial State Crown.
• Cullinan III — 94.4 carats, pear brilliant; set in the finial cross of Queen Mary's Crown; detachable as a brooch with Cullinan IV.
• Cullinan IV — 63.6 carats, cushion brilliant; set in the band of Queen Mary's Crown; detachable as a brooch with Cullinan III.
• Cullinan V — 18.8 carats, heart brilliant; set in a brooch.
• Cullinan VI — 11.5 carats, marquise brilliant; set in a necklace.
• Cullinan VII — 8.8 carats, marquise brilliant; pendant to a brooch.
• Cullinan VIII — 6.8 carats, oblong brilliant; set in a brooch.
• Cullinan IX — 4.4 carats, pear brilliant; set in a ring.

Further Reading

• GIA Gems & Gemology — Type IIa Diamonds and the Cullinan Legacy
• GIA — Famous Diamonds Research