Cullinan VI is an 11.5-carat marquise-shaped diamond, the sixth-largest of the nine principal stones cut from the Cullinan rough — the largest gem-quality diamond crystal ever discovered. Polished by Joseph Asscher & Co. of Amsterdam in 1908 and presented to Queen Mary in 1910, the stone is classified as a Type IIa diamond, a designation indicating an almost complete absence of nitrogen impurities and, consequently, a degree of optical transparency and colourlessness that places it among the rarest of all diamond categories. Today Cullinan VI forms the principal element of a brooch it shares with Cullinan VIII, a companion stone of 6.8 carats, the two together composing an elegant marquise-and-emerald-cut drop design that has been worn by successive British queens and remains one of the most recognisable pieces in the Royal Collection.

The Cullinan Rough: Discovery and Division

The story of Cullinan VI begins on 26 January 1905, when Frederick Wells, surface manager of the Premier Mine near Pretoria in the Transvaal (present-day South Africa), observed a glinting object protruding from the mine wall at a depth of approximately nine metres. The crystal he extracted weighed 3,106.75 carats — roughly 621 grams — and was named after Sir Thomas Cullinan, the mine's owner. Its size was so extraordinary that initial reports were met with scepticism; the stone was widely assumed to be a fragment of a larger crystal, though no matching counterpart was ever found.

The Transvaal government purchased the rough in 1907 for £150,000 and presented it to King Edward VII as a gift on his sixty-sixth birthday. The king entrusted the stone to Joseph Asscher & Co., the Amsterdam firm whose reputation for precision cleaving was then unmatched in the trade. The task of studying the crystal's internal structure, grain, and cleavage planes occupied Asscher's craftsmen for several months before a single blow was struck. On 10 February 1908, Joseph Asscher himself cleaved the stone — reportedly fainting from the tension immediately afterwards, though the cleave itself was executed flawlessly.

The rough ultimately yielded nine major polished stones (designated Cullinan I through IX), ninety-six smaller brilliants, and nine carats of unpolished fragments. The nine principal stones ranged from the 530.20-carat Cullinan I (the Great Star of Africa, set in the Sovereign's Sceptre with Cross) to the 4.39-carat Cullinan IX. Cullinan VI, at 11.5 carats, occupied sixth place in this hierarchy of weight.

Gemological Character

Like all nine principal Cullinan stones, Cullinan VI is a Type IIa diamond. This classification, established through infrared spectroscopy and confirmed by laboratories including the Gemological Institute of America, identifies diamonds in which nitrogen — the most common impurity in diamond — is present at levels too low for detection by standard spectroscopic methods. The practical consequence is a stone of exceptional colourlessness and, frequently, of superior transparency across the ultraviolet spectrum. Type IIa diamonds account for fewer than two per cent of all gem diamonds, and the Cullinan family represents perhaps the most celebrated cluster of such stones in recorded history.

The marquise (or navette) outline of Cullinan VI — an elongated elliptical form with pointed ends — was not an arbitrary aesthetic choice. Asscher's craftsmen worked to maximise the yield from each section of the rough while preserving the optical performance of the finished stone. The marquise cut, with its elongated facet arrangement, suited the particular geometry of the rough section from which Cullinan VI was derived, and its proportions allow the stone to display the broad, open table and lively scintillation characteristic of well-cut diamonds of this period. The cutting style reflects early twentieth-century practice rather than the mathematically optimised modern round brilliant, yet the stone's inherent material quality ensures that its performance remains remarkable.

Presentation to Queen Mary

Following the polishing of the nine principal stones, the British government retained Cullinan I and Cullinan II, which were set into the Crown Jewels. The remaining seven principal stones were returned to the Asscher firm as partial payment for their labour — a commercially unusual arrangement that reflected both the difficulty of the commission and the diplomatic complexities of the gift's origins. King Edward VII subsequently purchased Cullinan III through IX from Asscher for Queen Alexandra.

In 1910, following Edward VII's death and the accession of George V, Cullinan VI and Cullinan VIII were presented to Queen Mary. The precise circumstances of the transfer are consistent with the broader pattern by which the smaller Cullinan stones were distributed within the Royal Family during the early years of the twentieth century. Queen Mary, whose passion for jewellery and whose systematic approach to assembling and documenting the Royal Collection are well attested, commissioned the brooch setting that united the two stones.

The Brooch: Design and Construction

The brooch in which Cullinan VI is mounted pairs it with Cullinan VIII in a drop configuration. Cullinan VI, as the larger and more visually dominant stone, forms the upper element in its marquise orientation, while Cullinan VIII — an emerald-cut (oblong step-cut) diamond — hangs below as a pendant drop. The design is sometimes described as the marquise-and-emerald-drop brooch, a name that distinguishes it from the several other Cullinan-stone brooches in the collection.

The setting is characterised by the restrained platinum-and-diamond aesthetic that dominated fine jewellery in the Edwardian period and the early decades of the twentieth century: a delicate open framework that allows light to pass through the stones from multiple angles, with small accent diamonds enhancing the overall brilliance without competing with the principal gems. The brooch is designed so that Cullinan VIII can be detached and worn independently, a practical flexibility that Queen Mary and her successors have exploited on numerous occasions.

The brooch occupies a dual role within the Royal Collection. It functions as a standalone piece of considerable importance, and it also forms part of the Delhi Durbar parure, an assemblage of jewels associated with the Delhi Durbars of 1903 and 1911 — the great imperial ceremonial gatherings held in India to mark the accessions of Edward VII and George V respectively. The parure, which incorporates emeralds alongside diamonds, was worn by Queen Mary at the 1911 Durbar and has been associated with major state occasions ever since. The combination of Cullinan VI's colourless brilliance with the deep green of the parure's emeralds exemplifies the chromatic contrasts that defined Edwardian and early Georgian court jewellery.

Royal Provenance and Subsequent Wear

Queen Mary wore the brooch extensively throughout her long tenure as queen consort and later as queen mother, and it passed in due course to Queen Elizabeth II, who inherited the bulk of Queen Mary's personal jewellery collection in 1953. Queen Elizabeth II was photographed wearing the brooch on numerous occasions across her seventy-year reign, sometimes as part of the Delhi Durbar parure and sometimes as an independent piece. Following the death of Queen Elizabeth II in September 2022, the jewels of the Royal Collection passed to the Crown, with personal items subject to the customary arrangements governing royal inheritance.

The brooch's appearances at state occasions, Commonwealth events, and formal portraits have made it one of the more photographically documented pieces in the collection, notwithstanding the greater fame of Cullinan I and Cullinan II. Its relatively modest size — by royal standards — renders it versatile in a way that the great sceptre stone and the Imperial State Crown stone are not: it can be worn at the throat or on a lapel without the visual weight that would overwhelm a less formal costume.

Cullinan VI in the Context of the Nine Principal Stones

To appreciate Cullinan VI properly, it is useful to situate it within the full sequence of principal stones:

• Cullinan I — 530.20 carats, pear-shaped brilliant; set in the Sovereign's Sceptre with Cross.
• Cullinan II — 317.40 carats, cushion-shaped brilliant; set in the Imperial State Crown.
• Cullinan III — 94.40 carats, pear-shaped; part of Queen Mary's Crown, later worn as a pendant.
• Cullinan IV — 63.60 carats, cushion-shaped; set in Queen Mary's Crown, later worn as a brooch.
• Cullinan V — 18.80 carats, heart-shaped; set in a brooch that can also be incorporated into the Delhi Durbar stomacher.
• Cullinan VI — 11.50 carats, marquise; mounted with Cullinan VIII in the marquise-and-emerald-drop brooch.
• Cullinan VII — 8.80 carats, marquise; pendant to a brooch incorporating Cullinan VIII at certain configurations, or worn independently.
• Cullinan VIII — 6.80 carats, oblong brilliant (emerald-cut); mounted with Cullinan VI.
• Cullinan IX — 4.39 carats, pear-shaped; set in a ring.

The grouping of Cullinan VI with Cullinan VIII is therefore a deliberate pairing of the sixth- and eighth-largest stones, a combination chosen for aesthetic complementarity — the marquise outline of VI contrasting elegantly with the rectangular step-cut of VIII — rather than strict numerical adjacency. Cullinan VII, the other marquise in the sequence, has its own separate setting history.

Joseph Asscher & Co. and the Art of Cleaving

The firm responsible for producing Cullinan VI was founded in Amsterdam in 1854 by Joseph Isaac Asscher and had, by the early twentieth century, established itself as the pre-eminent diamond-cutting house in the world. The commission to cleave and polish the Cullinan rough was the most consequential single assignment in the firm's history. The Asscher family's contribution to diamond cutting extends beyond the Cullinan commission: the Asscher cut — a square step-cut with deeply cropped corners and a distinctive optical pattern — was patented by the firm in 1902 and remains one of the canonical diamond cuts of the twentieth century. The firm, now operating as Royal Asscher Diamond Company following a royal warrant granted by Queen Juliana of the Netherlands in 1980, continues to trade in Amsterdam.

The technical challenge of the Cullinan commission lay not merely in the stone's size but in the requirement to plan the division of a single crystal into multiple finished gems of varying shapes while minimising waste and avoiding the internal fractures and inclusions that could compromise the finished stones. The fact that the nine principal Cullinan diamonds are all of exceptional clarity — Cullinan VI included — is a testament to the quality of the original rough and to the skill with which Asscher's craftsmen navigated its internal architecture.

Type IIa Diamonds and Scientific Significance

The Type IIa classification of Cullinan VI carries significance beyond the trade. Type IIa diamonds have been subjects of scientific study because their nitrogen-free lattice structure makes them useful analogues for understanding diamond formation under extreme mantle conditions. Research published in Gems & Gemology and elsewhere has established that many large Type IIa diamonds — including several of the Cullinan stones — originate at depths considerably greater than those typical of most gem diamonds, forming in the sublithospheric mantle at depths exceeding 360 kilometres. These stones are sometimes termed superdeep diamonds, and their inclusions, when present, can contain mineral phases that provide direct evidence of conditions in the deep Earth. Cullinan VI, like its siblings, is thus not merely a jewel of historical and aesthetic importance but a geological specimen of scientific interest.

In the Trade and the Market

Cullinan VI has never appeared at public auction and, as part of the British Royal Collection, is not available for private sale. Its value is therefore theoretical rather than market-tested. However, comparable Type IIa marquise diamonds of exceptional colour and clarity — though far smaller and without the provenance of a Cullinan stone — have achieved prices at major auction houses that illustrate the premium the market places on this material category. The combination of Type IIa classification, Cullinan provenance, royal ownership history, and the irreplaceable nature of the stone as one of nine principal gems from the world's largest recorded diamond crystal would, in any hypothetical sale scenario, place it in a category beyond conventional price comparison.

For collectors and students of important diamonds, Cullinan VI represents a convergence of factors — geological rarity, historical significance, technical craftsmanship, and royal association — that is unlikely to be replicated. The Premier Mine (subsequently renamed the Cullinan Mine) continues to produce exceptional diamonds, including the 507.55-carat Cullinan Heritage rough in 2009, but no crystal approaching the scale of the original Cullinan has been recovered in the intervening century.

Further Reading

• GIA Gems & Gemology — Cullinan Diamond History
• GIA — Diamond Quality Factors (Type IIa context)
• Lotus Gemology — Gemological Library