How Are Diamonds Made?

Key takeaway: Natural diamonds form deep inside the earth under intense heat and pressure over very long timescales, then get carried towards the surface by volcanic activity. Lab-grown diamonds are chemically identical to natural ones but are created in a controlled setting and usually sell for less. If you want to know what your stone is really worth, The Gold Avenue in Illovo, Sandton, tests and values it against the four Cs in front of you, with same-day payment.

Few things hold our attention quite like a diamond. We admire them in engagement rings, in inherited jewellery and in watches, yet most of us have never paused to ask where they actually come from. Understanding how a diamond is made is not just satisfying curiosity. It directly shapes what a stone is worth, how a buyer assesses it, and whether the price you are offered is fair when the time comes to sell.

At The Gold Avenue, the luxury watch, gold and diamond exchange in Illovo, Sandton, Johannesburg, we value diamonds every week for sellers across Gauteng. This guide explains how natural diamonds form, how lab-grown diamonds are produced, why the difference matters for value, and how a reputable buyer reads a stone against the four Cs. Knowing the basics puts you in a stronger position whether you are insuring, comparing or selling.

How natural diamonds form

Natural diamonds are made of carbon, the same element found in pencil lead and in the soot from a candle. The difference lies entirely in how that carbon is arranged. A diamond’s carbon atoms are locked into a tightly bonded crystal structure, and it is that structure that gives the stone its famous hardness and brilliance.

This arrangement only happens deep within the earth, where conditions are extreme. Far below the surface, intense heat and immense pressure act on carbon over very long timescales, slowly forcing the atoms into the diamond crystal lattice. The result is a rough crystal that may sit undisturbed for an enormous span of time before anything brings it closer to us.

How diamonds reach the surface

A diamond that forms deep underground would stay there forever without a way up. That route is provided by volcanic activity. Powerful eruptions originating from great depth carry diamond-bearing rock upward, depositing it in formations that can later be mined. In other words, the diamond in a ring did not form where it was found. It travelled a long way from where it was created, carried by forces far older than any of us.

Because every natural diamond follows its own path through heat, pressure and time, no two are identical. Tiny internal features, slight differences in colour and variations in shape all tell the story of how an individual stone came to be. A trained eye can read those features, which is part of how a buyer tells one stone from another.

How lab-grown diamonds are made

Not every diamond comes from the ground. Lab-grown diamonds, sometimes called created or cultivated diamonds, are produced in a controlled environment rather than over geological time. The important point to understand is that they are chemically identical to natural diamonds. They are real diamonds in the material sense, made of the same carbon in the same crystal structure, not imitations like cubic zirconia or glass.

There are two main methods used to grow them.

• HPHT (High Pressure, High Temperature): This method recreates conditions similar to those found deep in the earth. Carbon is exposed to high pressure and high temperature so that it crystallises into diamond.
• CVD (Chemical Vapour Deposition): This method builds a diamond layer by layer from a carbon-rich gas inside a chamber, allowing the crystal to grow gradually onto a starting seed.

Both methods produce genuine diamond material. To the naked eye, a well-made lab-grown stone can look just like a natural one, which is exactly why proper testing and grading matter so much when value is on the line.

Why the difference matters for value

Here is where formation meets the wallet. Although natural and lab-grown diamonds are chemically the same, the market does not treat them the same way. Lab-grown diamonds typically sell for less than natural stones. A natural diamond carries the scarcity of something formed over an immense timescale and then recovered, while a lab-grown diamond can be produced more readily.

This matters enormously when you sell. If you assume a stone is natural when it is in fact lab-grown, or the other way round, your expectation of its worth can be far off. A reputable buyer needs to establish which kind of diamond you have before quoting anything, because the two sit at different points in the market. This is one of the reasons a stone should be assessed by someone who tests properly rather than estimated by eye or by a stamp on a setting.

What this means for older jewellery

Inherited and vintage pieces are usually set with natural diamonds, simply because lab-grown stones became widely available more recently. Even so, a buyer will not assume. The responsible approach is to examine the stone itself, confirm its characteristics, and value it on what it actually is rather than on what a setting or a family story suggests.

The four Cs: how a stone is judged

Whether a diamond is natural or lab-grown, its quality is described using the four Cs. These are the language the whole trade uses, and understanding them helps you follow any valuation you are given.

• Cut: How well the diamond has been shaped and faceted. Cut governs how the stone handles light, which is what produces sparkle. A precise cut can make a stone far more appealing than its size alone would suggest.
• Colour: Many diamonds are graded on how little colour they show, with stones nearer to colourless generally sitting higher in value. Colour is assessed carefully because small differences can be hard to see without training.
• Clarity: The presence of tiny internal features and surface marks. Cleaner stones, with fewer visible inclusions, tend to be valued more highly.
• Carat: The weight of the diamond. Weight is one of the clearest factors in value, though it always works together with the other three Cs rather than on its own.

No single C tells the whole story. A large stone with a poor cut may be worth less than a smaller, beautifully cut one. A good buyer weighs all four together, alongside whether the diamond is natural or lab-grown, to arrive at a fair figure.

Diamond shapes you may have

Shape is related to cut but describes the outline of the stone. Common shapes include round brilliant, princess, emerald, oval, cushion, marquise, pear, radiant, asscher and heart. The round brilliant is the most familiar, though each shape has its own following. Knowing the shape of your stone is a small but useful detail to have ready before a valuation.

Why certification helps

A diamond certificate, sometimes called a grading report, is an independent assessment of a stone’s characteristics from a recognised laboratory. The GIA is the most recognised grading lab, and a report from a respected lab describes the diamond’s qualities in a consistent, trusted way.

Certification helps you in two practical ways. It raises buyer confidence, because the stone’s grading has been verified by an independent party rather than asserted by the seller. It also supports resale value, since a documented diamond is easier to assess and trust. If you have paperwork for your diamond, keep it safe and bring it along. If you do not, that is not a problem in itself, since a capable buyer can still examine and value the stone directly.

How The Gold Avenue values a diamond when you sell

When you bring a diamond to The Gold Avenue in Illovo, the process is built around transparency. You watch what happens to your stone and you are under no obligation to accept the offer. The steps are straightforward.

1. Bring your stone and any paperwork. If you have a grading report or original purchase documents, bring them. They are helpful but not essential.
2. The diamond is examined. We assess the stone in front of you, establishing its characteristics and whether it is natural or lab-grown.
3. It is graded against the four Cs. Cut, colour, clarity and carat are considered together to build an accurate picture of the diamond.
4. You receive a clear, market-based offer. The valuation reflects what the stone actually is, priced against current market conditions, with our international dealer network, particularly in the UAE, helping us pay local sellers more competitively.
5. You decide, and we pay the same day. If you accept, payment is made the same day by cash or EFT. If you would rather not sell, you simply take your diamond home.

Checklist before you sell a diamond

A little preparation makes the whole visit smoother. Run through this short list before you come in.

• Gather any grading reports, certificates or original purchase receipts you have.
• Note the shape of your stone if you know it.
• Bring the diamond in its setting, or loose, whichever you have.
• Bring your FICA documents: a South African ID or passport, plus proof of address.
• Decide whether you would prefer payment by cash or EFT.
• Come with questions. A good buyer should be happy to explain the valuation.

If you would like to talk through your piece before visiting, the team at The Gold Avenue is easy to reach. You can call or send a WhatsApp message, and we are based in Illovo, Sandton, within easy reach of greater Johannesburg.

The Gold Avenue
Illovo Point, 68 Melville Road, Illovo, Sandton, 2196
Phone: 010 109 0080
WhatsApp: 076 393 5429

Frequently asked questions

Are lab-grown diamonds real diamonds?

Yes. Lab-grown diamonds are chemically identical to natural diamonds. They are made of the same carbon in the same crystal structure, produced by HPHT or CVD methods rather than forming in the earth. They are genuine diamond material, not imitations. The main practical difference is that they typically sell for less than natural stones.

How can you tell a natural diamond from a lab-grown one?

You usually cannot tell by eye, which is precisely why proper assessment matters. A reputable buyer examines the stone properly to establish which kind it is, since the two sit at different points in the market. At The Gold Avenue we do this in front of you before making any offer.

Do I need a certificate to sell my diamond?

No, a certificate is helpful but not required. A grading report from a recognised lab raises buyer confidence and supports value, so bring it if you have one. If you do not, a capable buyer can still examine and value your diamond directly. We assess every stone on its own characteristics.

How does The Gold Avenue decide what my diamond is worth?

We grade the stone against the four Cs, Cut, Colour, Clarity and Carat, confirm whether it is natural or lab-grown, and price it against current market conditions. Our international dealer network, particularly in the UAE, helps us pay local sellers more competitively. You see the process and are never obliged to accept.

Learn More

At The Gold Avenue, we simplify the process of selling your valuable assets. From luxury watches and Krugerrands to gold, diamond jewellery, and more, we offer fast, safe, and convenient buying services, coupled with an enjoyable experience. We stand by our promise to provide the best price for your items.

Krugerrands: Sell your Krugerrands swiftly and securely.

Gold Jewellery: Turn your gold jewellery into instant cash.

Gold Coins: Get the best price for your gold coins.

Diamonds: Exchange your diamonds for a competitive price.

Watches: Luxury watches like Rolex and others are welcome.

In need of a cash loan? We’ve got you covered.

Selling to The Gold Avenue is simple:

Contact Our Team: Reach out to our team via call, WhatsApp, or online chat. Describe the luxury items you want to sell.

Book an Appointment: Set a valuation appointment at a time convenient to you. Our safe and secure premises are located in Johannesburg.

Get an Offer: Our expert team will provide a quick and fair valuation. We’re committed to long-term relationships, guaranteeing the best price.

Money in Your Bank: We offer immediate payments, directly into your bank account, either through cash or EFT.

Ready to start selling? Book an Appointment