Understanding Diamond Inclusions: What They Are and Which Ones Matter
Understanding Diamond Inclusions: What They Are and Which Ones Matter
Almost every diamond has inclusions. They are the tiny crystals, fractures and growth marks sealed inside the stone as it formed, and they are the reason clarity exists as a grade at all. The useful question is not whether a diamond has them. It is which ones it has, where they sit, and whether you would ever see them.
That distinction is where money is saved or spent without reason. Two stones one grade apart can look identical on the hand while one costs noticeably more, and a single badly placed fracture can matter more than a dozen harmless specks.
Diamond inclusions, at a glance
Inclusions are features inside the stone. Blemishes sit on its surface. Both are judged at 10x magnification.
The clarity scale runs across eleven grades, from Flawless (FL) to Included (I3). Eye-clean means nothing is visible face up without magnification.
Most inclusions are harmless. Feathers that reach the surface or sit near the girdle are the ones that deserve a closer look.
For value: brilliant cuts hide inclusions well and step cuts reveal them, so an eye-clean VS2 or SI1 brilliant is where many buyers land.
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View Piece →What Diamond Inclusions Are, and How They Form
Most natural diamonds formed between one and three billion years ago, roughly 150 to 200 kilometres below the surface, where carbon crystallizes under intense heat and pressure. That growth is never perfectly tidy: the crystal can trap grains of other minerals, tiny diamonds of its own, or pockets of irregular structure. Stress during growth, or during the fast journey to the surface in volcanic rock, can open small fractures. Everything sealed inside the finished stone is an inclusion.
Blemishes are different. They sit on the outside of the polished diamond: a polish line, a small nick at the girdle, a scratch on the table, or a patch of original crystal skin the cutter chose to leave. Blemishes weigh less in the grade because many can be polished away.
No two diamonds share the same pattern of inclusions. Our diamond clarity guide covers the grading process step by step; here, the focus is on the features themselves.
The Inclusion Types You Will See on a Report
A grading report names the main features in a stone and marks their positions on a plotted diagram. These are the ones that appear most often.
| Inclusion | What it is | Typical effect |
|---|---|---|
| Pinpoint | A very small crystal that looks like a dot at 10x | Rarely visible; harmless on its own |
| Cloud | A cluster of pinpoints, sometimes too fine to see individually | Harmless when small; a large, dense cloud can make a stone look hazy |
| Crystal | A mineral grain trapped during growth, sometimes another diamond | Depends on size and color; a dark crystal under the table is the most visible |
| Needle | A long, thin crystal shaped like a fine rod | Usually harmless |
| Feather | A small fracture that looks white and feathery from the side | The one to watch; a durability concern when it reaches the surface or the girdle |
| Knot | An included crystal that reaches the surface | Can show as a slight raised area on a facet; check where it sits |
| Cavity | An opening in the surface, often left where a crystal came loose during polishing | Can collect dirt; watch the edges for chipping |
| Twinning wisp | A ribbon of pinpoints, clouds or crystals formed where the crystal's growth shifted direction | Usually mild, and common in stones that grew with a twinning plane |
| Indented natural | A piece of original crystal skin that dips below the polished surface, usually at the girdle | Rarely visible face up |
For each feature, a grader weighs five things: size, number, position, nature and relief. Relief is how strongly the feature contrasts with the stone around it. That is why a small dark crystal in the centre of the table can lower a grade more than a larger, colorless feather tucked against the girdle.
The Clarity Scale, From Flawless to Included
Clarity is graded face up and through the pavilion under 10x magnification, by trained graders working in controlled light. The scale has eleven grades in six groups.
Flawless (FL) shows no inclusions and no blemishes at 10x. Internally Flawless (IF) shows no inclusions, only minor surface blemishes. Both are genuinely rare in natural stones.
Very Very Slightly Included (VVS1, VVS2) stones have features so minute that a skilled grader struggles to find them at 10x. Very Slightly Included (VS1, VS2) stones have minor inclusions that take some effort to locate under magnification.
Slightly Included (SI1, SI2) stones have inclusions that are noticeable at 10x. Included (I1, I2, I3) stones have obvious inclusions at 10x, and at the lower end they can affect transparency, brilliance and durability.
Eye-clean is not an official grade, but it is the phrase that matters most in practice. It means that when you look at the stone face up, at a normal distance of 25 to 30 centimetres and without magnification, you see no inclusions. Nearly every VS2 stone is eye-clean, a large share of SI1 stones are, and some SI2 stones are too, especially smaller round brilliants. Of the 4Cs of diamond grading, clarity is the one where the gap between paper and life is widest.
The report tells you what a grader saw at ten times magnification. Eye-clean tells you what you will see across the dinner table.
Which Inclusions Affect Durability, and Which Are Harmless
Diamond is the hardest natural material, but hardness measures resistance to scratching, not to breaking. Diamond also has cleavage planes, directions along which a hard, well aimed knock can split it, and a few inclusions make that more likely.
Feathers are the main concern. A feather sealed deep inside the stone affects appearance and little else. A feather that reaches the surface, especially at the girdle, is an open crack at the stone's thinnest and most exposed edge, and a sharp blow or careless pressure during setting can extend it. The same goes for feathers at the points of a pear, marquise or princess cut, where the stone is already vulnerable. Large surface-reaching cavities and knots can also chip under hard wear.
Pinpoints, needles, small clouds, twinning wisps, indented naturals and small enclosed crystals are, in almost every case, harmless to durability. If a report plots a feather, ask where it is and whether it breaks the surface. For an engagement ring worn every day, a surface-reaching feather near the girdle is a reason to choose a protective setting or a different stone.
How Shape and Setting Hide or Reveal Inclusions
Brilliant cuts are forgiving. Round, oval, pear, cushion, radiant and princess shapes break the view into a busy pattern of small reflections that camouflages minor inclusions well, though the same reflections can occasionally mirror one crystal several times across the crown. Why facet patterns change the look of a stone is covered in our guide to what makes a diamond sparkle.
Step cuts are candid. An emerald cut or asscher cut has long, open facets and a broad table that act almost like windows. An inclusion that disappears in a round brilliant can sit in plain view in a step cut, so many buyers move up to VS1 or better for these shapes. Our diamond shapes guide covers how each outline wears.
Settings play their part. A skilled setter can place a small edge inclusion beneath a prong, though never so that a prong presses on a feather. A bezel wraps the girdle in metal and protects a vulnerable edge completely. A halo hides nothing within the centre stone.
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View Piece →Inclusions in Lab Grown Diamonds
Lab grown diamonds have inclusions too, and they are graded on the same scale. What differs is the type, because the growth methods leave their own signatures.
HPHT diamonds, grown under high pressure and high temperature, crystallize from a molten metal solvent. Traces of that metal can be trapped as metallic flux inclusions: opaque, dark and sometimes reflective, and in larger amounts enough to make a stone weakly magnetic. CVD diamonds grow layer by layer from a carbon-rich gas onto a seed plate. Their typical features are dark pinpoints of non-diamond carbon and graining, faint lines of strain that follow the growth layers.
These features help a grading laboratory confirm origin, nothing more; a well grown lab grown diamond is eye-clean at the same grades as a mined one. Our comparison of natural and lab grown diamonds covers what else separates the two.
Clarity Enhancement and What Must Be Disclosed
Some diamonds are treated to make inclusions less visible. The two common methods are very different, and both should be disclosed before you buy.
Laser drilling bores a hair-fine channel from the surface to a dark crystal, which is then bleached or dissolved. The result is permanent, though the tiny drill hole stays visible under magnification. Grading laboratories will grade a laser drilled diamond and note the treatment on the report.
Fracture filling injects a glass-like substance into feathers so they show less. It often reveals itself as colored flashes when the stone is tilted, and it is not permanent: the heat of a jeweler's torch during a repair, or harsh cleaning, can damage or cloud the filling. Many grading laboratories will not issue a clarity grade on a filled stone at all.
Under US trade guidance, sellers must disclose treatments that are not permanent, that need special care, or that significantly affect value. Ask directly and read the comments section of the report. Our guide on how to read a diamond certificate shows where treatment notes appear.
How to Buy Clarity for Value
Buy eye-clean, not the highest letters you can reach. For round brilliants and other brilliant shapes up to around one and a half carats, a well chosen VS2 or SI1 usually looks exactly like a flawless stone at normal distance. For step cuts and larger stones, where inclusions have more room to show, VS1 or better is the safer range.
Then read the plot, not just the grade. Inclusions near the edge beat those in the centre of the table, white or colorless features beat dark ones, and surface-reaching feathers at the girdle or at points are best avoided. Then view the stone face up at arm's length, the way you will actually wear it.
Whatever you save on clarity is best spent on cut, which decides how bright a stone looks. Our guide to how diamond pricing works shows how steeply price climbs between neighboring grades. For diamond earrings and pendants, seen from farther away, the SI range and well chosen I1 stones make sense.
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View Piece →Frequently Asked Questions
Are inclusions in a diamond bad?
Not in themselves. Nearly all diamonds have them, and most are invisible without magnification and harmless to durability. What matters is the type, size and position of each one, which is why reading the report plot tells you more than the grade alone.
What clarity grade is eye-clean?
Most VS2 stones and many SI1 stones are eye-clean face up, and some SI2 round brilliants are as well. Step cuts and larger stones show more, so VS1 or better is a safer choice there. The only sure test is looking at the stone itself without magnification.
Can an inclusion cause a diamond to crack?
Rarely, and almost always because of a feather that reaches the surface, particularly at the girdle or at a point. A hard knock in the wrong place can extend such a feather. Enclosed inclusions such as pinpoints, needles and small crystals pose no practical risk.
Do lab grown diamonds have inclusions?
Yes. HPHT stones can contain metallic flux from the metal solvent they grow in, and CVD stones can show dark pinpoints and graining along their growth layers. They are graded on the same clarity scale as mined diamonds.
Does clarity affect how a diamond sparkles?
Only at the lower grades, where large or numerous inclusions block light. Across the eye-clean range, cut has far more influence on sparkle than clarity does, which our sparkle guide explains in detail.
What is a fracture-filled diamond?
A diamond whose feathers have been filled with a glass-like substance to make them less visible. The treatment is not permanent and can be damaged by heat during repairs, so it must be disclosed. Many grading laboratories will not grade filled stones.
Now you know what the words on a report mean and which of them deserve your attention. Start with an eye-clean stone, check the plot for feathers at the edge, and put the difference into cut. Browse our diamond rings or the wider fine jewelry collection to put it into practice.
Find an eye-clean diamond that suits the way you live.
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