Every diamond carries its own internal fingerprint — inclusions formed as the stone crystallised deep within the earth over a billion years or more. They help gemologists identify a diamond, and they influence both its clarity grade and its price. Here is what to know before you buy.
What are diamond inclusions?
Inclusions are natural internal features formed during a diamond's growth — trapped minerals, tiny fractures, or irregularities in the crystal structure itself. They vary in size, shape, number and position. Some are visible only under 10x magnification, the standard used by gemologists; others can be seen with the naked eye, which is what separates the higher clarity grades from the lower ones. Related surface-level marks are called blemishes rather than inclusions, since they sit on the outside of the stone — scratches or nicks picked up after cutting, for example.
Common types of inclusions
- Pinpoint: tiny crystals that look like small dots under magnification — among the most common and usually the least visually significant.
- Feather: thin, wispy fractures resembling feathers; their impact on both appearance and durability depends heavily on size, depth and position within the stone.
- Cloud: clusters of microscopic pinpoint crystals that, if large or dense enough, can create a hazy or milky look and slightly reduce brilliance.
- Crystal: solid mineral crystals trapped inside during formation, varying in size and colour — a small colourless crystal has little effect; a large dark one is more noticeable.
- Knot: a crystal that reaches the diamond's surface, which can affect both clarity grade and, in some cases, structural durability if positioned near an edge.
- Cavity and chip: small openings or breaks at the surface, often related to an inclusion close to the girdle or a facet edge.
How the clarity scale works
The GIA clarity scale — used industry-wide, including by IGI — runs across six categories and eleven grades:
- FL / IF (Flawless / Internally Flawless): no inclusions visible under 10x magnification. Extremely rare.
- VVS1 / VVS2 (Very, Very Slightly Included): inclusions so minor they are difficult even for a trained grader to find under magnification.
- VS1 / VS2 (Very Slightly Included): minor inclusions visible under magnification, not visible to the naked eye.
- SI1 / SI2 (Slightly Included): inclusions noticeable under magnification, sometimes visible without it depending on size and position.
- I1 / I2 / I3 (Included): inclusions visible to the naked eye that may affect transparency and brilliance.
Fewer and less visible inclusions mean a higher clarity grade — and a higher price. But clarity is only one of the 4Cs; see our companion piece on GIA certificates and diamond types for how it fits alongside cut, colour and carat.
Where inclusions matter most — and where they don't
Position matters as much as size. An inclusion hidden under a prong once the stone is set, or tucked near the edge of the girdle, will likely never be seen in daily wear. The same inclusion sitting directly under the table — the large flat facet on top of the stone — is far more visible, because that's exactly where your eye and any light entering the stone are focused. This is why two diamonds with the same clarity grade can look noticeably different: the grade tells you how much is there, not always exactly where.
"Eye-clean" — the practical sweet spot
A diamond is considered eye-clean when its inclusions are invisible to the naked eye at a normal viewing distance, even if they are visible under magnification. Many SI1 and some SI2 stones are eye-clean, offering a real saving over VS or VVS grades with no visible difference once the stone is set. This is often the best value zone for buyers who want to maximise carat weight or budget for a better cut grade instead.
Choosing the right diamond for you
Flawless and Internally Flawless diamonds command the highest prices for their rarity, but stones with slight, eye-clean inclusions can offer excellent value without any visible difference once worn. The right choice depends on your budget, the setting, and how the stone will be worn day to day. A skilled jeweller can also advise on which inclusions matter for durability versus appearance when helping you choose a specific stone.
Learn the fundamentals in our beginner's guide to GIA certificates and diamond types, compare lab-grown and natural diamonds, or browse our certified diamond jewellery — every stone we sell comes with its GIA or IGI lab report.
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