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Diamond flaws are common. Few diamonds are perfect; most of them have inclusions or imperfections. These inclusions are also known as flaws and exist in various forms, such as exterior and interior. Inclusions are also classified in the manner in which they were formed. For example, syngenetic diamond inclusions are inclusions which were formed while a diamond formed, while epigenetic inclusions occurred after a diamond was formed.
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Flaws
The presence or absence of flaws or inclusions in a diamond is usually decided by examining the stone carefully with a lens having the standard magnifications of 10x. No other magnification should be taken as authoritative. Stones which show no apparent flaws or inclusions under this magnification are regarded as flawless. The term for a scarcely perceptible inclusion is "VVS" for "very very slight (or small)" – which is sometimes offered as flawless. Slightly larger flaws or groups of very thin inclusions are termed "VS" ("very slight"). Larger flaws or inclusions are termed as "SI" (or slightly included). Even larger flaws are termed as "1st pique". Slightly larger flaws classify the stone as "2nd pique" and so on.
Any flaws which are visible with the naked eye would be sufficient to scale the price down considerably.
Internal flaws
Every natural diamond crystal contains impurities and typical intrinsic or "self-defects": vacancies, dislocations, and interstitial atoms. The most common impurity in diamond is nitrogen, which can comprise up to 1% of a diamond by mass. Nitrogen as a diamond impurity was first identified in 1959 by Kaiser and Bond of Bell Telephone.
Crystal/mineral inclusions
Some diamonds show the presence of small crystals, minerals or other diamonds. These are classified in different categories depending on the size and structure of the inclusion. While many such inclusions are small and invisible to the naked eye, some diamonds may have large inclusions able to be seen with the naked eye, and can affect a diamond's clarity and life. Some crystals resemble a diamond inside a diamond and may also add to the appearance of the stone. These take on shapes of bubbles, needles or grains and are classified as below.
Pinpoint inclusions
As the name implies, these inclusions are minute crystals usually white in color present inside the diamond. These resemble a small point of light and are, by far, the most common of all flaws found in diamonds. Most pinpoint inclusions do not affect the clarity of a diamond and are not visible to the naked eye and are usually not indicated on the plotting diagrams of diamond reports. Comments such as "pinpoints not shown" may be listed in the comments section.
Needles
Diamond crystals in a diamond can also be present in the form of long and thin needles. These may not be visible to the naked eye, unless the needle inclusion is of a noticeable color or has a noticeable presence. Some needle inclusions are also known to give diamonds a special look.
Cloud
The presence of three or more pinpoint inclusions close together can create an area of haze, or a cloud, in the diamond. While the occurrence of a small cloud is not visible to the naked eye, presence of many pinpoints covering a large area can affect the clarity of the diamond. These are usually indicated on grading reports in the form of tiny red dots close together or as circles and other formations.
Knots
When diamond crystals extend to the surface of the diamond, they are referred to as knots. These can be viewed under proper lighting conditions with a diamond loupe. Certain knot formations may also cause raised areas on particular facets of the diamond. The presence of knots may affect both the clarity and durability of the diamond and are best avoided.
Graining
Crystal inclusions in diamonds occurs in the form of lines known as graining. Graining should not be confused with a rough diamonds natural grain lines . Graining forms due to the improper crystallization of the diamond or when a diamond is twinned. Twinned diamonds are two diamonds that have grown together and causes cross-grains within the diamond during its growth / crystallization process. Twinning causes natural lines, planes or cross-grains in a diamond. Graining can't be removed during the polishing process of a diamond as it is a natural plane within the diamond. Cross-graining also makes the polishing process extremely difficult for diamond cutters as a diamond only cuts against its natural grain lines and never with the grain. One will always find graining in rough diamonds known as "Macle's". Macles are easily identified by its triangular shape. The graining line on the Macle is a natural cleaving plane where the diamond can easily be split in half. Diamonds with graining will never be graded as Flawless as its maximum grade would only fetch Internally Flawless (IF). Although graining seems like a severe flaw it is not visible with the naked eye and does not impact the overall brilliance or quality of a diamond.
Feathers
These are cracks in the stone that resemble the design of feathers. The presence of feathers in a diamond usually does not affect the life of the stone unless and until the feather runs through a major length of the stone or shows major stress points where it can break. If the cracks reach the surface or have deep fissures, the durability of the stone may be reduced with the possibility of the stone breaking with age.
Intergrowths
Twinning wisps or intergrowths may also be seen in diamonds. These formations are usually inclusions in diamonds that have twisted together during the time of diamond formation. Thus, various inclusions such as pinpoints, needles or feathers may form together, creating a white strip inside the diamond. Surface graining may also be seen in some cases. Such intergrowths are more commonly seen in fancy cut diamonds and are extremely rare in ideal cut diamonds.
Cleavage
These are cracks in a diamond that occur in a straight line and are parallel to one of the diamond's crystallographic planes. Cleavages are usually caused by deep internal strain in a diamond and could also have been caused by a strong blow to the diamond. It usually shows no feathers and has a great chance of causing the stone to split, especially if placed in the high pressure grip of prongs in rings. Stones with cleavage must be chosen carefully and avoided as often as possible.
Etch channel
Etch channels are created during a diamond's formation process deep in the Earth. In the journey of the rough diamond to the Earth's surface, the contact with high-temperature fluids etches into the diamond's crystalline structure which often leave parallel lines or irregularly shaped tunnel-like structures.
Bearding
Also known as girdle fencing or "dig marks", this is caused around the diamond's girdle as the diamond is cut or bruted. These fine lines usually resemble a strand of hair and do not present a problem. However, extensive bearding can lessen the brightness of the diamond. It is suitable that such diamonds be cut or polished again to improve luster.
Diamond flaws are not always negative features. In fact, these flaws often lend a diamond its distinctive beauty and make a stone look unique.