Diamonds are the most popular gemstone in the world, but most of the science and history behind them is hidden behind marketing slogans. Here are ten facts about diamonds that go beyond the usual 4Cs introduction — useful whether you are about to buy your first diamond or just curious about the stone itself.
Diamonds are pure carbon formed 150-200km underground over 1-3 billion years, are the hardest natural substance (Mohs 10), and have refractive index 2.42 — which is why they sparkle. Roughly 30% of mined diamonds are gem-quality. The largest ever found weighed 3,106 carats (the Cullinan). The UK 2025 average engagement-ring spend is £3,928, with over 60% of buyers now choosing lab-grown stones.
1. Diamonds are the hardest natural mineral on earth
Diamond scores 10 on the Mohs hardness scale — the maximum. Nothing in nature scratches a diamond except another diamond. This is why diamond-cutting wheels use diamond powder embedded in metal; nothing else is hard enough to shape one. Hardness is also what makes diamond ideal for daily wear: a well-set diamond engagement ring lasts a lifetime with only routine cleaning.
2. Most diamonds are around a billion years old
Natural diamonds form roughly 150 kilometres below the earth's surface under intense pressure and temperature. Most diamonds being sold today are between 1 and 3.5 billion years old. They reach the surface through deep-source volcanic eruptions called kimberlite pipes, which last erupted on this planet around 70 million years ago — so every mined diamond is essentially being recovered, not actively produced.
3. Diamond is the only gemstone made of a single element
Diamond is pure crystallised carbon — the same element as graphite (the soft, dark material in pencil leads) and as the carbon in living tissue. The difference is structural: in diamond, each carbon atom bonds covalently to four others in a rigid three-dimensional lattice, creating the strongest material structure in the natural world. In graphite, carbon atoms bond into flat sheets that slide easily, which is why graphite is soft.
4. Diamonds are not actually rare
Gem-quality diamonds are much less rare than the 20th-century marketing campaigns suggested. The De Beers cartel controlled global diamond supply for most of the 1900s, deliberately restricting market release to maintain prices and the "rare and precious" narrative. Today, around 120 million carats of rough diamonds are mined annually. What is genuinely rare is large, well-cut, high-clarity stones — and increasingly, fancy-coloured naturals (pink, blue, red).
5. The diamond engagement ring tradition is largely a marketing invention
Engagement rings have existed for centuries, but the diamond engagement ring as the default became a tradition only after the De Beers "A Diamond is Forever" campaign launched in 1947. Before that campaign, only about 10% of US engagement rings featured a diamond. Within twenty years, that figure was over 80%. The "two months' salary" rule for ring spending was a De Beers marketing slogan from the 1930s, not an old custom.
6. Lab-grown diamonds are chemically identical to mined diamonds
A lab-grown diamond is real carbon in the same crystal structure as a mined diamond. The FTC, GIA, and IGI all formally classify lab-grown stones as diamonds, not as simulants or substitutes. The only difference is production method (a controlled reactor over 2–4 weeks instead of geological formation over a billion years). Pricing is typically 60–70% lower for equivalent grades.
7. Diamonds come in every colour of the spectrum
Most diamonds we see are colourless or near-colourless, but diamonds occur naturally in yellow, brown, pink, blue, green, orange, purple, red, and black. Trace elements and structural defects produce the colour: boron creates blue diamonds, nitrogen creates yellow, structural distortion produces pink and red. Red diamonds are the rarest of all — fewer than 30 pure red diamonds are known to exist publicly.
8. The largest gem-quality diamond ever found was 3,106 carats
The Cullinan diamond, discovered in 1905 in South Africa, weighed 3,106.75 carats (621 grams) in its rough form. It was cut into 105 finished stones, the largest of which (Cullinan I, also called the Great Star of Africa) is 530.4 carats and set in the Sovereign's Sceptre of the British Crown Jewels. The second-largest fragment (Cullinan II) sits in the Imperial State Crown.
9. Diamonds can burn
Because diamond is pure carbon, it can be ignited in a high-oxygen environment at temperatures above about 800°C. The reaction produces carbon dioxide and leaves no residue — the diamond effectively disappears. Antoine Lavoisier demonstrated this in 1772 by focusing sunlight through a magnifying glass onto a diamond. In normal jewellery wear there is no risk; a diamond cannot accidentally burn without sustained, very high heat in a pure-oxygen environment.
10. The 4Cs grading system is only about 70 years old
The 4Cs (cut, colour, clarity, carat) framework that defines modern diamond grading was developed by Robert M. Shipley at the Gemological Institute of America in the 1940s and 1950s. Before this, diamond quality was assessed by a wide variety of inconsistent regional standards. The GIA grading scale (D-Z for colour, FL-I3 for clarity) became the global standard and remains the reference today, with IGI and GCAL providing equivalent grading using the same scales.
Frequently Asked Questions
What is the most expensive diamond ever sold?
The Pink Star, a 59.6-carat oval-cut pink diamond, sold at Sotheby's Hong Kong in April 2017 for $71.2 million — the highest price ever paid for any diamond at auction. Fancy-coloured diamonds dominate the top of the auction market because of their extreme rarity; a flawless pink or blue diamond of high carat weight is genuinely one-of-a-kind.
Are diamonds a good investment?
For most buyers, no. Standard white diamonds depreciate substantially from retail price — second-hand resale typically returns 30–50% of original purchase value. Exceptional pieces (D-IF flawless, large fancy-colour, historic provenance) hold value better but require specialist auction-house sale. If you want a wearable asset, buy what you love and treat the value question as secondary.
How are diamonds graded?
Diamonds are graded on the 4Cs (cut, colour, clarity, carat weight) by independent gemological laboratories. The GIA (Gemological Institute of America), IGI (International Gemological Institute), and GCAL (Gem Certification & Assurance Lab) all issue reports with the same grading framework. A reputable jeweller will always provide the lab report and the certificate number is laser-inscribed on the diamond's girdle for verification.
Can you really tell a real diamond from a fake?
At a basic level, yes. A real diamond will not fog up when you breathe on it (the heat dissipates instantly); will sink in water; and will scratch glass. For confidence, use a jeweller's diamond tester (which measures thermal conductivity — diamond conducts heat far better than any imitation) or take the stone to a jeweller with proper equipment. The most reliable test is the lab report number laser-inscribed on the girdle of any certified diamond.
Browse certified diamond jewellery at Reve
Every diamond at Reve Diamonds is independently certified by the GIA or IGI. Browse our engagement rings collection or visit our London showroom to see certified diamonds across every shape, size, and colour grade in person.
