Inclusions are features inside a diamond, and blemishes are features on its surface. Nearly every natural diamond has some, because diamonds grow under great heat and pressure deep in the Earth and trap other minerals and strain as they form. Graders map them on a plot diagram and use their size, number, position, nature and relief to set the clarity grade. This library describes the common types and notes which ones can weaken a stone.
How inclusions affect a diamond
Most inclusions affect only appearance, and many are too small to see without 10x magnification. A few can affect durability, especially feathers and cavities that reach the surface or sit near the girdle, where a knock in wear concentrates stress.
On a grading report, red symbols on the plot mark internal features and green symbols mark external ones. The report also lists the features that set the grade, starting with the most important.
| Type | Inside or surface | Durability concern |
|---|---|---|
| Pinpoint | Inside | None |
| Cloud | Inside | Rarely; very large clouds can reduce transparency |
| Crystal | Inside | Low, unless large or surface-reaching |
| Feather | Inside, may reach surface | Yes, especially when large or near the girdle |
| Knot | Reaches surface | Possible |
| Needle | Inside | None |
| Twinning wisp | Inside | Low |
| Internal graining | Inside | None |
| Cavity | Surface | Possible; collects dirt |
| Chip | Surface | Possible, depending on size and location |
| Laser drill hole | Inside, opening at surface | Low |
Internal features
Pinpoint
A pinpoint is a tiny crystal that looks like a white or dark dot at 10x. Pinpoints are the most common diamond inclusion. A single pinpoint can be the only feature in a VVS or higher stone.
Cloud
A cloud is a cluster of pinpoints too close together to show individually. It looks like a hazy patch. Small clouds have little effect. A large cloud can make part of a stone look milky and lower the grade, even in otherwise clean stones.
Crystal
A crystal is a mineral grain trapped in the diamond while it grew. Common included minerals are garnet (often red or orange), olivine, diopside and other diamonds. Some included crystals are dark, such as graphite or sulfides; the trade often calls these "carbon spots," though most are not pure carbon. Dark crystals near the table are more visible than white ones near the girdle. Included minerals also tell scientists about the depth and conditions of growth (see diamond geology).
Feather
A feather is a fracture inside the diamond. At magnification it looks white and wispy, often like a feather, and can look transparent from some angles. Small feathers deep inside the stone are harmless. Large feathers, or ones reaching the surface or near the girdle, can grow with a hard knock or with heat from a jeweler's torch.
Feathers are the inclusions most worth checking before buying. Fracture filling (below) targets feathers that reach the surface.
Knot
A knot is an included diamond crystal that reaches the surface of the polished stone. Because the crystal grain runs differently from the host diamond, the polisher cannot make it smooth, and a raised area remains. Knots can be seen with reflected light and sometimes felt.
Needle
A needle is a long, thin crystal that looks like a short rod. Needles often appear in groups and cause no durability problem.
Twinning wisp
A twinning wisp forms along a twinning plane, where the crystal changed growth direction. It looks like a twisted ribbon of pinpoints, clouds or crystals. Twinning wisps are common in diamonds cut from twinned crystals such as macles.
Internal graining
Internal graining appears as faint lines, angles or curves inside the stone, caused by irregular crystal growth or strain. It can look whitish, colored or reflective. Strong graining can make a stone look hazy. Pink and brown diamonds often show colored graining, because the same deformation that causes the graining also causes the color (see fancy colored diamonds).
Bearding
Bearding is a set of fine feathers along the girdle that form during bruting when the girdle is rounded too fast. Heavy bearding can give the girdle a fuzzy look. It is common in older stones.
Growth tubes
Growth tubes are hollow or filled channels that form as the diamond grows. They are less common than other features and look similar to needles but open in places.
Surface features
Cavity
A cavity is an opening in the surface, often left when a crystal or part of a feather is pulled out during polishing. Cavities can collect dirt and oil and may weaken the stone if large.
Chip
A chip is a small notch, often at the girdle, culet or facet junctions, caused by a blow. Chips can be removed by repolishing, with some weight loss.
Natural
A natural is a small area of the original crystal surface left on a polished stone, usually on the girdle. Cutters leave naturals to save weight. A natural on the girdle that does not extend into the crown or pavilion often does not affect the clarity grade.
Indented natural
An indented natural is a natural that dips below the polished surface of the stone. It is more visible than a flat natural and can affect the grade.
Other blemishes
Graders also note polish lines, scratches, abrasions (tiny nicks along facet junctions), nicks, pits, burn marks from polishing and extra facets. These usually affect the polish grade and, in high clarity grades, the clarity grade.
Treatment features
Laser drill holes
A laser drill hole is a tiny tunnel from the surface to a dark inclusion. Workshops drill to the inclusion, then use acid to bleach it or dissolve it. The tunnel looks like a fine white thread at magnification. Laser drilling is a permanent treatment that labs disclose on the report.
A related method called internal laser drilling (sometimes called KM drilling) uses heat from a laser to extend a feather to a dark inclusion so acid can reach it. It leaves irregular, worm-like channels.
Fracture filling
Fracture filling forces a glass-like material into feathers that reach the surface. The filling hides the feather by matching the diamond's refractive index more closely than air. Filled fractures show a "flash effect": colored flashes, often orange or blue, when the stone is tilted. Fillings can be damaged by heat, so jewelers need to know before repairing. GIA does not issue grading reports for fracture-filled diamonds. See diamond treatments for more.
Inclusions in lab-grown diamonds
Lab-grown diamonds have their own features. HPHT-grown stones can contain metallic flux inclusions from the growth chamber, which may make the stone attracted to a strong magnet. CVD-grown stones can show dark pinpoints of non-diamond carbon and growth layers that look like faint banding. Labs use these features, along with spectroscopy, to identify lab-grown diamonds.
Inclusions and buying
Most buyers do not need a flawless stone. An eye-clean diamond, one with no inclusions visible to the unaided eye at a normal viewing distance, often falls in the VS and sometimes SI grades. The type and position of inclusions matter more than the grade alone. A white crystal near the girdle is easier to live with than a dark crystal under the table or a feather near a prong. Grading labs use much the same terms, though their reports present them differently.
Frequently asked questions
Which diamond inclusions are the most serious?
Large feathers reaching the surface or near the girdle, and large cavities or knots, carry the most risk to durability. Dark crystals under the table affect appearance most.
What is a carbon spot in a diamond?
It is a trade term for a dark included crystal. Most are other minerals or graphite, not pure carbon specks.
Can inclusions be removed from a diamond?
Some can be bleached through laser drilling or hidden with fracture filling, and some surface features can be polished away. These treatments are disclosed on reports and affect value.
Do lab-grown diamonds have inclusions?
Yes. They can contain metallic flux, dark carbon pinpoints or growth lines, which labs use to identify them.