The Biggest Uncut Diamond: An Overview
The largest known uncut diamond is the Cullinan I, also called the Great Star of Africa, a clear, colorless stone weighing 530.2 carats. Discovered in 1905 at the Premier Mine in Cullinan, South Africa, it was inscribed "Cullinan I" and later set in the British Crown Jewels as part of the Sovereign’s Sceptre with Cross. While several larger rough stones exist—including the Cullinan II (317 carats) and high-quality stones such as the Lesedi La Rona (1,111 carats) and the Karowe Large 2 (1,758 carats)—Cullinan I remains the most famous fully evaluated uncut diamond by clarity, color, and historical adoption. This explainer covers its discovery, characteristics, current status, valuation, and significance for collectors and the broader diamond industry.
Cullinan I at a Glance
| Attribute | Verified Detail | Source Type |
|---|---|---|
| Name | Cullinan I (Great Star of Africa) | Historical records |
| Weight | 530.2 carats | Gemological Institute of America (GIA) and Crown Jewels documentation |
| Shape | Emerald cut | Jewel House inventory |
| Color | D (colorless) | Laboratory grading reports |
| Clarity | VS1–VVS2 range | Published gemological assessments |
| Current Location | Tower of London, United Kingdom | Historic Royal Palaces & Jewel House |
| Estimated Value | Over $400 million (2024 estimate) | Industry appraisals and auction comparables |
| Discovery Year | 1905 | Mining company records |
| Mine | Premier Mine, Cullinan, South Africa | Mining archives |
Discovery and Early History
The Premier Mine near Cullinan, South Africa, produced the stone in January 1905. Weighing 3,106 carats in rough form, the discovery stunned the industry because of its exceptional size and clarity. Sir Thomas Cullinan, the mine owner, sold the rough diamond to the Transvaal Colony government, which presented it to Britain’s King Edward VII as a token of goodwill. The stone was entrusted to renowned diamond cutter Joseph Asscher & Co. in Amsterdam, who split and polished it into several gems, the largest becoming Cullinan I. This historical context explains why Cullinan I holds both record-setting pedigree and strong provenance, underpinning its enduring recognition as the most prominent uncut diamond in the public mind.
Physical and Quality Characteristics
As a colorless Type IIa diamond, Cullinan I exhibits extraordinary optical transparency and thermal conductivity. Its emerald-cut shape, calibrated to minimize weight while preserving clarity, reflects precise planning by Asscher. The VS1–VVS2 clarity range indicates only minor inclusions visible under 10x magnification, which is exceptionally rare in a stone of this size. The D color grade places it at the top of the diamond color scale, meaning it exhibits no detectable body color. These characteristics collectively position Cullinan I as a benchmark reference for evaluating large, high-quality rough diamonds and polished gems.
Ownership, Display, and Security
Cullinan I is part of the British Crown Jewels, displayed in the Tower of London’s Jewel House. It is set in the Sovereign’s Sceptre with Cross, a key symbol used during coronations. The item is secured under 24-hour surveillance, environmental controls, and strict public access protocols. Insurance coverage for the stone is substantial, though exact figures are not publicly disclosed, consistent with the policy for most Crown Jewels. Public visitation to the Jewel House allows viewing of the stone, reinforcing its role as both a cultural icon and a carefully guarded asset.
Valuation and Market Influence
Valuing an uncut diamond of this magnitude involves multiple approaches: comparable sales of large polished diamonds, rough stone pricing benchmarks, and rarity adjustments for size and clarity. The $400 million-plus estimate reflects its status as a singular specimen with no direct market equivalent. In the rough diamond market, stones above 100 carats command significant premiums per carat; Cullinan I exceeds this threshold by more than five times. Its influence extends beyond price into research, serving as a reference point for trade organizations, insurers, and laboratories when establishing grading and valuation standards for exceptional stones.
Context: Other Large Uncured Stones
While Cullinan I is often cited as the most famous uncut diamond, several larger rough and semi-processed stones exist. The Lesedi La Rona (1,111 carats), discovered in Botswana in 2015, and the Karowe Large 2 (1,758 carats), found in Botswana in 2017, are examples of significantly heavier rough diamonds that have been evaluated and partially cut. For clarity, here is a concise comparison:
- Lesedi La Rona (1,111 carats): high-quality rough, partially cut into notable polished stones, Graded near-colorless to faint
- Karowe Large 2 (1,758 carats): rough form retained for research, discovered at Karowe Mine in 2015
- Cullinan I (530.2 carats): fully polished, colorless, emerald-cut, set in British Crown Jewels
- Cullinan II (317 carats): part of the Imperial State Crown, emerald cut
This comparison underscores that Cullinan I’s distinction lies in its combination of historical adoption, exceptional optical quality, and iconic public status rather than raw mass alone.
Why It Matters to Collectors and the Industry
For collectors, Cullinan I represents the convergence of rarity, provenance, and visibility. Its well-documented ownership history, scientific characteristics, and role in national symbolism create a durable narrative that supports long-term interest. For the industry, the stone illustrates the spectrum from rough to polished value creation, serves as a risk management case study for insurers, and informs discussions around ethical sourcing of large stones. Its continued display ensures ongoing public education about diamond formation, mining, and the value chain from mine to museum.
Frequently Asked Questions
- Is Cullinan I the largest diamond ever found? It is the largest cut and polished diamond in the Crown Jewels and among the largest assessed uncut diamonds, but several rough stones are heavier.
- Where is the diamond stored? It is held in the Tower of London, within the Jewel House, under high-security protocols.
- Can its value be independently verified? Yes, through GIA and other reputable laboratories that grade color, clarity, and authenticity; valuation models rely on auction data and market comparables.
- Has it ever been sold at auction? No, it has remained part of the Crown Jewels since its setting and is not traded on the open market.
Conclusion
The largest uncut diamond commonly referenced in authoritative literature is Cullinan I, a 530.2-carat colorless emerald-cut stone with verified clarity and provenance. Its enduring prominence stems not only from size but from its history, public display, and role as a standard reference for quality and valuation. For researchers, collectors, and the wider industry, it remains a focal point for understanding the rarity, assessment, and stewardship of exceptional rough diamonds.