What Makes a Diamond Special? The Science, Rarity and Australian Story

What makes a diamond special?

Three things set diamond apart from every other gem. First, its structure: it is pure carbon, with every atom locked to four neighbours in a rigid cubic lattice, which makes it the hardest natural material known. Second, its optics: light slows down more in diamond than in almost any other natural transparent gem, so a well-cut stone sends back bright white light and flashes of colour. Third, its story: a natural diamond grew deep in the Earth's mantle, usually more than a billion years ago, and survived a violent volcanic trip to the surface.

No other gem combines all three. Sapphire is very hard but much less bright. Zircon and demantoid garnet have plenty of fire (flashes of rainbow colour) but scratch and chip far more easily. Moissanite, a lab-created gem, shows more fire than diamond but is a little softer and has a busier, rainbow-heavy look that not everyone likes. Diamond sits at the balance point: tough enough to wear every day for a lifetime, and bright enough to read across a room.

This guide covers the science, the rarity and the Australian chapter, then finishes with how to make your own engagement ring around a natural diamond. For the wider picture on grading and buying, start with our complete guide to natural diamonds. If a word here is new to you, the GemTrove jewellery glossary explains it in plain English.

Why is diamond the hardest natural material?

Diamond and graphite, the grey material in a pencil, are made of exactly the same element: carbon. The difference is how the atoms are arranged. In graphite, carbon sits in flat sheets that slide over each other, so it is soft (about 1–2 on the Mohs scale). In diamond, every carbon atom is joined to four others by very short, very strong covalent bonds (bonds where atoms share electrons), forming a three-dimensional framework with no weak direction for a scratch to follow. Same atoms, different arrangement: that is the gap between a pencil lead and an engagement ring.

The Mohs scale ranks minerals by which one scratches which, from talc at 1 to diamond at 10. It is a ranking, not a measurement, so the steps are uneven. Sapphire and ruby (corundum) sit at 9, yet on instrument tests diamond is roughly three to four times harder than corundum. In practice, the only thing that scratches a diamond is another diamond, which is why cutters polish diamonds with diamond powder.

Hardness is not the same as toughness (resistance to chipping and breaking). Diamond has cleavage: four directions, parallel to the faces of its natural eight-sided crystal, along which it can split if it takes a sharp knock at the wrong angle. Historically, cutters used this to split rough stones on purpose. For you, it means a diamond will not scratch from everyday wear, but a thin girdle (the edge around the widest part) or a sharp point can still chip against a hard surface.

Diamond has one more unusual property: it conducts heat extremely well, roughly five times better than copper. That is why a diamond feels cold when you touch it to your lip, and why the handheld testers jewellers use measure how quickly heat moves through a stone. Moissanite also conducts heat well, so modern testers add an electrical check to tell the two apart.

What makes a diamond sparkle?

Sparkle starts with the refractive index (RI), a measure of how much a material slows and bends light. Light travels about 2.42 times slower in diamond than in air. A high RI gives diamond a small critical angle of about 24.4°: light hitting an inside facet at more than that angle from the perpendicular cannot escape and is reflected back into the stone. A cutter sets the pavilion (the lower half) at an angle of roughly 40.6–41° on a round brilliant so that light entering the top bounces off the pavilion facets and comes back out through the crown towards your eye.

• Brilliance: the white light returned from the stone. Diamond's high RI and its adamantine lustre (the hard, mirror-like shine of its polished surface) make this strong.
• Fire: flashes of spectral colour, caused by dispersion, the way a material splits white light into colours. Diamond's dispersion of 0.044 is high for a natural colourless gem.
• Scintillation: the pattern of light and dark flashes you see as the diamond, the light or your eye moves.

All of this depends on the cut. The same rough crystal can be cut into a bright stone or a glassy, dark one. A diamond cut too deep looks smaller face-up and dark in the centre; one cut too shallow spreads wider but leaks light and can show a dull grey ring called a fish-eye. Our guide on making a diamond look bigger without adding carats explains how proportions change the size you actually see, and the right mount helps too, as our page on ring settings that make a centre stone look larger shows.

One everyday point: diamond attracts oil and grease, so skin oils and hand cream quickly dull a ring. A soak in warm water with a drop of dishwashing liquid and a soft brush brings the sparkle straight back.

How are diamonds formed, and how old are they?

Most natural diamonds grew in the Earth's upper mantle, about 150–200 km below the surface, at roughly 900–1,300 °C and pressures around 45,000–60,000 times the air pressure at sea level. Under those conditions, carbon in fluids and molten rock crystallised as diamond rather than graphite. A small group of super-deep diamonds formed far lower again, from around 300 km to beyond 660 km, and their tiny mineral inclusions (trapped crystals) give scientists rare samples of the deep Earth.

Dating those inclusions shows most natural diamonds are between about 1 and 3.5 billion years old, so the stone in a ring is often older than complex life on Earth. Diamonds do not form in coal seams, despite the popular story; most are far older than land plants.

Diamonds reach the surface inside kimberlite or lamproite, rare types of volcanic rock that erupt from great depth unusually fast. Speed matters: at the surface, diamond is not the stable form of carbon. It only survives because the conversion back to graphite is unimaginably slow at normal temperatures. A slow rise through hot rock would have destroyed many of them on the way up. The same deep-sourced magmas carry up other mantle minerals, including olivine; its gem form is covered in our page on peridot, another gem brought up from the mantle.

Today the main producing countries include Russia, Botswana, Canada, the Democratic Republic of the Congo, South Africa, Angola, Namibia and, until 2020, Australia. Our overview of the world's main diamond mining regions compares them, and diamonds from Canada's Northwest Territories have their own page, since Canadian mines have operated since 1998.

Are diamonds rare?

The honest answer is: diamond as a mineral is not especially rare, but fine gem diamonds are. The world mines in the order of 100–120 million carats of natural diamond a year, and a large share of that is small, heavily included or brown material used for industrial abrasives or low-cost jewellery. Many mines recover well under one carat for every tonne of rock they process. A colourless, eye-clean natural diamond over one carat is a small fraction of the total.

Scientists also sort diamonds into types by the trace elements, mainly nitrogen and boron, inside the carbon lattice. Type affects colour and how a diamond reacts to treatment, and some types are genuinely scarce.

Type IIa stones include some of history's largest diamonds, and Type IIb is the type behind natural blues. Our page on the four diamond types, Ia, Ib, IIa and IIb explains how labs identify them and why the type also helps separate natural from lab-grown stones.

What makes an Australian diamond special?

Australia's place in diamond history comes mostly from one mine: Argyle, in the east Kimberley region of Western Australia. Its deposit was found in 1979, and it was unusual from the start: a lamproite rather than the more common kimberlite. Argyle was for years one of the world's largest producers by volume, though most of its output was small brown and champagne diamonds that the industry learnt to market rather than discard.

• Discovered: 1979; full-scale mining from 1985, moving underground in the 2010s.
• Closed: November 2020, after producing more than 865 million carats.
• Pink diamonds: the source of most of the world's natural pinks, along with rare reds and violets.
• Annual tender: the finest pinks were sold each year through an invitation-only tender.

Argyle pinks are a scientific curiosity as well as a rare gem. Their colour does not come from an impurity. It comes from plastic deformation: intense pressure in the Earth bent the crystal lattice slightly, changing how it absorbs light. Most Argyle pinks are small, often under half a carat, and with no major new source of comparable pinks, natural Argyle stones have become harder to find since the closure. Lab-grown pink diamonds exist, and must always be disclosed as lab-grown.

Argyle is not the whole Australian story. Alluvial diamonds (stones washed into river gravels) were found in New South Wales in the gold-rush era of the mid-1800s. The Ellendale mine in Western Australia produced fancy yellow diamonds until 2015, and the Merlin field in the Northern Territory yielded Australia's largest recorded diamond, of about 104.7 carats, in 1998. Read more in our history of the Argyle mine and Australian diamond finds, and see how Argyle pinks sit beside stones like the Hope and the Cullinan in a guide to the world's most famous diamonds.

Is a natural diamond more special than a lab-grown diamond?

Both are real diamond. A lab-grown diamond (also called laboratory-grown) is carbon crystallised as diamond in a laboratory, using either HPHT (high pressure, high temperature, copying mantle conditions in a press) or CVD (chemical vapour deposition, growing diamond layer by layer from a carbon-rich gas). It has the same hardness, refractive index and crystal structure as natural diamond. It is not a simulant like cubic zirconia or moissanite.

So which is more special depends on what matters to you. If you value the physical properties and the look, a lab-grown diamond delivers them at much lower cost. If the meaning lies in age and origin, a stone formed over a billion years ago and recovered from a particular place, only natural diamond offers that. Neither choice is wrong. Curious how lab growth actually works? Our page asking whether you could grow a diamond at home explains the equipment involved and why the answer is no.

Origin also raises sourcing questions. Since 2003 the Kimberley Process certification scheme has tracked rough diamond shipments between countries to block diamonds that fund armed conflict, though it has well-known limits. Our page on what responsible diamond sourcing involves sets out the questions worth asking any jeweller.

Why do diamonds mean so much to people?

The word diamond comes from the Greek adamas, meaning unconquerable, and its reputation for permanence is centuries old. India was the main source of diamonds for most of recorded history, until Brazil's deposits were found in the 1720s and South Africa's in the late 1860s. The first well-documented diamond engagement ring was given in 1477, when Archduke Maximilian of Austria proposed to Mary of Burgundy.

Durability is what makes that symbolism practical. Because diamond does not scratch in normal wear, a diamond can pass through several generations and still look crisp. Older diamonds cut by hand, such as Old European and old mine cuts, have a softer, chunkier sparkle that many people now seek out; see our guide to antique and old-stock diamonds. A stone from a grandparent's ring can be lifted, checked and set again, and our page on giving a family diamond a new setting covers what a jeweller looks at first.

How do you make your own engagement ring with a natural diamond?

To make your own engagement ring, you are designing the setting around a stone you have chosen, rather than picking a finished ring from a case. It suits people who want a particular natural diamond, a family stone or a design nobody else has. A custom ring typically takes several weeks from first sketch to finished piece.

1. Decide on the shape and face-up size. Compare millimetre measurements, not just carat weight, and try a few shapes on your hand.
2. Choose the diamond with its report. Check the grading report from an independent lab such as GIA, confirming the diamond is natural, plus its cut, colour, clarity and measurements.
3. Consider stones you already own. A family diamond can become the centre stone or side stones once it has been checked for chips.
4. Pick the metal. Platinum and white gold suit colourless diamonds; yellow and rose gold warm the look and suit slightly warmer colours.
5. Review the CAD design. Check claw height, band width and how the ring will sit beside a future wedding band before anything is made.
6. Add the personal details. An engraving, a hidden side stone or a small profile detail makes the ring yours.
7. Plan the care. Have the claws checked about once a year and clean the diamond regularly to keep it bright.

Small touches are where a custom ring becomes personal; our ideas for hidden details inside a custom engagement ring range from engraved dates to a birthstone tucked under the centre diamond.