Diamond Inclusions | Which Ones to Avoid

Every natural diamond has inclusions. Even the highest grade flawless stones have microscopic features that distinguish them from one another. Inclusions are simply the natural identifying characteristics of a diamond, the internal features that formed during the billions of years the stone was developing under the earth.

The word "inclusion" sounds like a problem. It's not, at least not always. Some inclusions affect how a diamond looks and how much it's worth. Others are completely invisible to the eye and don't affect the appearance of the stone at all. Understanding the difference is the difference between paying for clarity you don't need and accepting flaws that actually matter.

This guide covers what inclusions are, the most common types, which ones to avoid, and how to evaluate them when you're shopping. If you're working through grading reports as part of your buying process, our post on how to read a diamond certificate covers the clarity scale in plain terms.

What Inclusions Actually Are

Natural diamonds form deep in the earth under extreme heat and pressure. During that formation, other minerals, gases, or structural irregularities can become trapped inside the carbon crystal. Those trapped features are inclusions. Surface features that aren't fully internal are called blemishes, and the GIA evaluates both when assigning a clarity grade.

The GIA's clarity grading system ranks stones from Flawless (FL) at the highest end to Included (I3) at the lowest. The grade reflects the size, number, position, nature, and visibility of inclusions under 10x magnification. For most buyers, the relevant range is VS2 (Very Slightly Included) through SI2 (Slightly Included), with VVS grades being significantly more expensive without producing a visible difference in the finished ring.

The single most useful concept to understand is "eye-clean," which means the inclusions are visible only under magnification, not to the naked eye. An eye-clean SI1 diamond looks identical to a flawless one in a ring setting. The difference is in the price, not the appearance.

The Most Common Types of Inclusions

Different inclusions affect a diamond in different ways. Some are practically invisible. Others change how light moves through the stone. A few can actually affect the structural integrity of the diamond. Knowing what you're looking at on a grading report changes how you evaluate a stone.

Crystals are tiny mineral inclusions trapped inside the diamond during formation. They can be other diamond crystals, garnet, peridot, or various other minerals. Crystals are extremely common and usually the most benign type of inclusion. Small, well-positioned crystals don't affect light performance and are often invisible without magnification. A larger crystal in a prominent position, particularly directly under the table, is more of a concern because it can be visible to the eye.

Feathers are small fractures inside the diamond, named because they often look like delicate feather-like patterns under magnification. Most feathers are stable and don't affect the integrity of the stone. The concern with feathers is when they reach the surface or extend across a large portion of the stone. A feather that breaks the surface, particularly on the girdle (the edge of the diamond), can theoretically grow under impact and is worth taking seriously. A small, contained feather away from the surface is generally fine.

Clouds are clusters of microscopic crystals or pinpoints that appear as hazy regions under magnification. Small, light clouds in non-prominent positions are typically eye-clean and don't affect appearance. Heavy clouds, particularly when they cover a significant portion of the stone, can give the diamond a milky or hazy appearance even without magnification. A grading report that lists "clouds not shown" or "clarity grade based on clouds" is worth examining carefully because heavy clouds can affect the visible quality of the stone in ways smaller pinpoint inclusions don't.

Pinpoints are extremely small crystals, often appearing as tiny dots under magnification. They're among the most benign inclusions. A diamond graded SI1 or SI2 based primarily on pinpoint inclusions is almost always eye-clean and is often a value opportunity because the grade is being driven by features that don't actually affect appearance.

Needles are long, thin crystal inclusions that look like fine lines or threads under magnification. They're usually small enough to be invisible to the eye and rarely affect a diamond's appearance.

Twinning wisps are flat, ribbon-like inclusions formed during the diamond's growth process when the crystal structure shifted. They appear as wavy lines or wispy patterns. Most twinning wisps are eye-clean and don't affect appearance, but heavier twinning can occasionally cause subtle haziness.

Cavities are open spaces on the surface of the diamond, sometimes left behind when a crystal inclusion was reached during cutting and removed. Cavities are blemishes rather than internal inclusions, and small ones are usually invisible. Larger cavities can collect dirt and oil over time and may need more careful cleaning.

Knots are crystal inclusions that reach the surface of the polished stone. They're a more significant concern because they can affect the structural integrity of the diamond and may catch on fabric or skin. Stones with surface-reaching knots are worth avoiding for engagement rings that will be worn daily.

Indented naturals are portions of the original rough diamond's surface that weren't fully polished away during cutting. They're typically located on the girdle and are often invisible without magnification. Most indented naturals are not a concern.

Which Inclusions to Avoid

The general rule is that the type, position, and size of an inclusion matter more than the clarity grade itself. A specific GIA grade can be eye-clean or visibly included depending on which features drove the grade.

The inclusions worth avoiding are those that affect either the appearance or the durability of the stone:

Surface-reaching feathers, particularly those crossing the girdle or extending into prominent positions, are a structural concern. They're not common, but they're worth noting on a grading report.

Heavy clouds that cover a significant portion of the stone can create a hazy or milky appearance, especially under certain lighting conditions. A grading report that mentions clouds as the primary clarity-grading feature warrants examination.

Knots that reach the surface can affect both durability and how the stone wears.

Large dark crystals in prominent positions, particularly directly beneath the table, can be visible to the naked eye even at higher clarity grades.

Inclusions that affect light performance, such as heavy twinning wisps or large feathers in the center of the stone, can interfere with brilliance even when they're not technically visible to the eye.

Inclusions That Are Almost Always Fine

The inclusions that are usually safe to accept are those that are small, well-positioned, and don't affect appearance:

Small crystals, particularly those positioned near the edge of the stone or hidden under a prong setting, are essentially invisible.

Pinpoints and small clouds in non-prominent positions don't affect appearance and often drive a stone into a more affordable clarity grade.

Small contained feathers that don't reach the surface are stable and invisible.

Indented naturals on the girdle are typically not detectable in a finished ring.

Light twinning wisps don't affect appearance and are extremely common.

A buyer who understands that an SI1 or SI2 stone with these types of inclusions can be visually identical to a VS1 stone has a meaningful advantage. They can buy the lower clarity grade at a significantly lower price point and end up with a stone that looks the same on the hand. Our post on why diamond prices vary so much covers how clarity premiums affect pricing in detail.

How Inclusions Affect Value

Clarity is one of the four Cs and contributes to a diamond's price, but its impact is non-linear. The premium between a Flawless stone and a VS1 is enormous, despite the visual difference being undetectable to almost any buyer in any setting. The premium between a VS1 and an SI1 is much smaller, and the visual difference is also undetectable when the SI1 is eye-clean.

This is one of the most consistent value opportunities in diamond buying. Going from a Flawless to a VS1 saves significant money for no visual change. Going from VS1 to a well-selected SI1 saves more money for no visual change. Going from SI1 to SI2 requires more careful evaluation because not all SI2 stones are eye-clean, but the ones that are represent strong value.

The factors that affect natural diamond value go beyond clarity alone. Our post on what makes a diamond valuable covers the full picture, including how rarity, cut quality, and provenance interact to determine what a stone is actually worth.

How to Evaluate Inclusions When You're Shopping

The most important rule is to look at the actual stone, not just the certificate. Two SI1 diamonds with identical certificates can look very different depending on which specific features drove the grade. One might be eye-clean and indistinguishable from a VS1; the other might have a visible inclusion right in the center of the table.

The plotting diagram on a GIA certificate shows the location of each inclusion. Inclusions on the periphery of the stone, particularly those that will be hidden under prongs in the final setting, are less of a concern than inclusions in the center of the table. A buyer who looks at the plotting diagram before evaluating the stone has a head start on understanding what they're looking for when they actually inspect it.

If you're buying remotely without seeing the stone in person, work with a source who can characterize the inclusions specifically rather than just citing the grade. A wholesaler who has actually examined the stone can tell you whether it's eye-clean, where the inclusions sit, and whether the clarity grade reflects the type of feature that affects appearance or the type that doesn't.

Want help evaluating the inclusions in a specific diamond? Book a Diamond Appointment and we'll walk through it with you.