Natural on a Diamond Girdle: What It Means, Risks and Report Symbols

What is a natural on a diamond girdle?

A natural is a small area of a polished diamond where the original surface of the rough crystal has been left unpolished. It almost always sits on the girdle, the narrow outer edge where the crown (the top half) meets the pavilion (the bottom half). Because it is on the surface rather than inside the stone, gemmologists class a natural as a blemish, not an inclusion.

Naturals are graded under clarity, one of the 4Cs of diamond grading, alongside colour, cut and carat. The word can be confusing: here "natural" describes the untouched crystal skin, not where the diamond came from. That is a separate question from the difference between natural, synthetic and simulant gems, and a natural on the girdle does not by itself prove a diamond was mined. If any other grading word trips you up, look it up in our jewellery glossary of grading terms.

Diamond is 10 on the Mohs hardness scale, with a refractive index of about 2.42. Polished facets act like tiny flat mirrors, but a natural has no polish, so it scatters light and looks frosted, matte or slightly grey under magnification. Most are small, often well under a millimetre across, and many are only visible with a 10× loupe (a jeweller's magnifier) looking at the edge of the stone.

How does a natural form, and why do cutters leave it?

Natural diamonds crystallise roughly 150–200 km below the surface, often as octahedra (eight-sided crystals shaped like two pyramids joined at the base). On the way up in volcanic rock such as kimberlite (or lamproite, as at Argyle), the crystal surface is partly dissolved and etched, which leaves the textured skin you see in a natural. Our guide to how natural diamonds grow deep in the mantle explains that journey in full.

A cutter's job is to get the most attractive, valuable diamond out of each piece of rough. The girdle is the widest part of a finished stone, so it is usually where the polished diamond comes closest to the outside of the crystal. If polishing the last trace of skin away would mean making the whole stone narrower and lighter, the cutter may leave a tiny natural instead.

• Weight retention: keeping a few points (hundredths of a carat; 1 point = 0.01 ct) can keep a stone above a size step such as 0.50, 0.70, 0.90, 1.00 or 1.50 ct.
• Spread: keeping the full girdle diameter means the stone faces up as large as possible for its weight.
• Proof of yield: some cutters see a small natural as a sign the stone was cut as close to the rough's maximum size as it could be.

Those size steps matter because prices jump at popular weights. For example, two natural rounds with the same colour and clarity at about 0.98 ct and 1.01 ct can differ by roughly AUD 1,000–3,000, even though nobody could tell them apart on the hand. That pricing pattern comes from why larger natural diamonds are rarer and priced higher per carat.

What does a natural look like under magnification?

Under a 10× loupe, a natural looks like a small rough or frosted patch interrupting the smooth band of the girdle. Look closely and you may see trigons (tiny triangular etch pits that form on octahedral crystal faces), fine parallel growth lines or a step-like texture. Some naturals are a little greyish or brownish because of the crystal's surface. Face-up, through the crown, almost all of them are invisible.

Several other girdle features can look similar at a glance, and telling them apart matters, because some are harmless and some are damage:

The one to watch is the indented natural, where the skin dips into the stone instead of lying flat. It is still original surface, but it breaks the line of the girdle and can sit closer to the inside of the diamond. Our page on indented naturals that dip below the girdle covers how they are graded and when they matter.

How is a natural on a diamond girdle shown on a grading report?

Full grading reports include a plotting diagram: a map of the diamond face-up and face-down showing where each clarity characteristic sits. On GIA and IGI plots, internal features (inclusions) are drawn in red and external features (blemishes) in green. A natural is normally drawn as a small green mark at the girdle edge and listed as "Natural" in the key to symbols. An indented natural may be drawn partly in red, because it reaches below the surface.

Not every natural gets plotted. Very small ones may only be mentioned in the comments, or covered by a general line such as additional clarity characteristics not shown. Shorter report formats, such as GIA's Diamond Dossier, have no plot at all. If a natural matters to you, read the key to symbols and the comments together; our guide to reading an IGI natural diamond report shows where each item sits on the page.

The report states the diamond's origin separately and clearly, so you never have to infer it from the clarity features. Our comparison of how natural and lab-grown reports differ explains the wording and the colour of each report.

Does a natural affect a diamond's clarity grade?

Usually not. Under GIA's definitions, a diamond can still be graded Flawless (FL) with a natural, as long as the natural is confined to the width of the girdle, does not thicken the girdle and does not distort its outline. Once it spreads onto the crown or pavilion facets, it starts to count.

In practice a girdle natural is almost always eye-clean, meaning you cannot see it without magnification at normal viewing distance. It sits at the edge, is seen side-on rather than through the table (the large top facet), and is often covered by a claw once set. A natural on the girdle also makes very little practical difference to how a stone is regarded later; for the wider picture, see how natural diamond prices have moved over the years.

Is a natural on a diamond girdle a durability risk?

The unpolished skin is the same diamond as the rest of the stone, so a natural is not a weak spot in itself. Diamond is very hard, but it can still split along its cleavage planes (directions where the crystal structure breaks most easily) if a thin edge takes a sharp knock. Risk comes from geometry: whether the natural makes the girdle locally thinner, cuts a notch into it, or sits next to a feather (a small internal crack). Our guide to how girdle thickness is measured and graded explains why a very thin girdle is the bigger concern.

Can lab-grown diamonds have naturals?

Yes, in the sense that matters for grading. Lab-grown diamonds are real diamond, grown by HPHT (high pressure, high temperature) or CVD (chemical vapour deposition) rather than mined. Their rough crystals also have an original growth surface, and a cutter can leave a small unpolished remnant at the girdle for the same weight reasons. Labs may plot it with the same natural symbol, because the term describes unpolished surface, not origin. Our side-by-side guide to lab-grown and natural diamonds compared covers the other differences.

So a natural is not evidence that a diamond was mined. Origin is confirmed with laboratory instruments, such as spectroscopy and fluorescence imaging, as explained in the testing labs use to confirm origin. Simple handheld devices are more limited, as our page on whether a handheld tester can separate natural from lab-grown explains.

Treatment does not remove naturals either. A mined diamond that has had its colour improved by HPHT keeps any natural on its girdle, and the report must disclose the treatment; see natural diamonds given HPHT colour treatment.

Can a natural be hidden by the setting or an engraving?

Often, yes. In a claw setting, the stone can be turned so the natural sits just beside a claw, where it is hidden from every normal angle. A bezel (a thin rim of metal around the edge) covers the entire girdle, so any natural vanishes and the edge is protected as well. Halo settings also shield the girdle from knocks.

Many diamonds carry a laser inscription on the girdle: usually the report number, sometimes a personal message. The inscriber chooses a smooth, polished stretch of girdle, so a natural simply changes where the text goes. If you are planning engraving a name or date on the girdle, it helps to know where the natural sits first.

How to check a natural before you buy: step by step

1. Read the plot and key. Find "Natural" or "Indented natural" in the key to symbols and locate the green mark at the girdle.
2. Check the comments. Small naturals may be noted there rather than plotted.
3. Look at the girdle grade. A natural on a thin or very thin girdle deserves a closer look than one on a medium girdle.
4. Look for neighbours. Make sure no feather or chip is plotted right beside the natural.
5. Ask for a magnified view. A 10× photo or video of the girdle shows whether it lies flat or dips into the stone.
6. Plan the setting. Decide which claw or bezel will protect that section of the girdle before the stone is set.

For most buyers, a girdle-only natural is a non-issue and can be a sensible trade-off for a stone that keeps its weight and spread. If you are still weighing up origin as well as clarity, our guide to choosing between natural and lab-grown stones for an engagement ring sets out the practical differences.