Diamond Inclusions Explained: Feathers, Crystals, Clouds and What They Mean
Every diamond grading certificate lists the inclusions present in a specific stone. The terms — feathers, crystals, clouds, needles, twinning wisps — describe very different things in terms of what the inclusion looks like, where it sits in the stone, and what implications it carries for durability and appearance. Understanding the main types helps you make a more informed decision when comparing certificates.
Why Inclusion Type Matters Beyond the Grade
Two diamonds can carry the same clarity grade — say, VS2 — and have very different inclusions. One might have a small crystal near the edge of the stone that is invisible to the naked eye and poses no structural concern. Another might have a feather (a fracture) in a less favourable location. Both are VS2; neither is wrong; but they are not equivalent from a practical standpoint.
Reading the inclusion type, not just the grade, tells you more about what you are actually buying.
Feathers
A feather is a small fracture within the diamond. When viewed under magnification at the right angle, it reflects light like a wispy white feather — hence the name. Feathers are fractures, which makes their location and size relevant to more than just appearance.
A small feather well away from the edge or girdle of the stone, at a VS2 or better clarity grade, is generally not a structural concern for normal wear. A larger feather reaching close to the surface or girdle, or positioned where it might be exposed to impact, warrants more careful evaluation. A diamond with an SI1 feather that extends close to the table surface would benefit from a protective setting and should be assessed carefully before purchase.
The practical question to ask: is this feather in a location where it could propagate (extend) under normal ring-wearing conditions? Your jeweller should be able to assess this from the grading report plot and the actual stone.
Crystals
A crystal is a mineral inclusion trapped inside the diamond during its formation. Most crystals are other diamond crystals or garnet inclusions and appear as small, dark or white pinpoints or irregular shapes under magnification.
Crystals are generally the most benign type of inclusion from a structural standpoint — they are enclosed within the diamond material rather than representing a break in it. Their significance is almost entirely visual: a crystal that is eye-visible reduces the stone’s appearance; one that is not visible to the naked eye has essentially no practical impact. At VS2 and above, most crystals are not a concern.
Clouds
A cloud is a cluster of very small pinpoint inclusions grouped together in a hazy formation. Individual pinpoints within a cloud may be below the resolution limit of 10x magnification; the cloud itself is what the grader is recording.
Clouds can range from insignificant to very significant depending on their density and extent. A faint, localised cloud that grades as VS2 and is invisible to the naked eye is not a practical concern. A dense cloud that covers a significant portion of the stone can cause milkiness or haziness — a reduction in the stone’s transparency and brilliance — that may not be fully captured by the clarity grade alone. GIA certificates note “clarity grade based on clouds not shown” when clouds are extensive enough to affect the grade but too numerous or diffuse to be mapped individually. This notation is worth noting when evaluating a stone.
Needles
Needles are long, thin crystal inclusions that look like tiny rods under magnification. They are often white or silver in appearance. Needles are generally benign — they are enclosed crystal structures, not fractures — and at VS2 and above they are rarely eye-visible. Multiple parallel needles grouped together may be more noticeable.
Twinning Wisps
Twinning wisps are inclusions that formed along a twinning plane — a structural boundary within the diamond crystal where two portions of the diamond grew in different orientations. Along this plane, various inclusion types can concentrate: clouds, needles, feathers, and crystals may all appear along a twinning wisp.
A faint twinning wisp at VS2 is not a practical concern. More prominent twinning wisps, particularly those that extend across a significant portion of the stone or that include feather-type elements along the plane, warrant more careful evaluation of both appearance and structural integrity.
Knots
A knot is a crystal inclusion that reaches the surface of the diamond. Because it extends to the surface, a knot is more structurally significant than an enclosed crystal — it represents a point where the diamond’s surface has been interrupted. Knots are relatively uncommon and appear more frequently at SI and I clarity grades. Where present, they affect polishing during cutting and can create a slightly elevated point on the stone’s surface.
Cavities and Chips
Cavities are small openings in the diamond’s surface where a crystal has been removed during polishing or where a surface-reaching feather has opened. Chips are surface indentations caused by damage during cutting, setting, or wear. Both are surface characteristics rather than internal inclusions. Chips on the girdle or near the culet are the most common post-purchase damage seen on engagement rings.
How to Use This When Buying
Ask your jeweller to explain the inclusions present in any specific stone you are considering. A GIA or IGI certificate includes a plot (a diagram of the stone with inclusion locations marked) that allows you to see where each inclusion sits relative to the stone’s outline and to the setting prongs. Combined with a knowledge of inclusion types, this gives you a much more complete picture than the clarity grade alone.
For brilliant-cut diamonds (round, oval, cushion), inclusions are less visible than in step cuts (emerald, Asscher). An SI1 round brilliant that is eye-clean in person is a good-value choice. The same logic in an emerald cut requires more caution — VS2 is the more reliable threshold for step cuts where inclusions have nowhere to hide.