Last updated on May 11, 2022
Diamond inclusions are clarity characteristics that develop when the diamond is formed deep in the earth. The size, quantity, placement and colour of these inclusions determine a stone’s clarity grade and affect its price. This guide brings together types of diamond inclusions to give you an idea of what they mean and how they affect the stone.
What Are Diamond Inclusions?
Since diamonds form under extreme heat and pressure and their growth takes between one to three billion years, only rare diamonds emerge in flawless condition. Most of them are imperfect and contain different clarity characteristics, which affect a diamond’s appearance, internal structure, clarity grade and price.
Depending on their nature, clarity characteristics are classified into diamond inclusions (internal features) and blemishes (external features).
Diamond inclusions or those internal features that extend into the diamond from its surface include bearded girdle, bruise, cavity, chip, cloud, crystal, feather, grain centre, indented natural, internal graining, internal laser drilling, knot, laser drill hole, needle, pinpoint and twinning wisp. These flaws can be either minor or serious, depending on the way light travels within the stone.
Diamond blemishes or external clarity characteristics are limited to the surface of a stone. They include abrasion, burn marks, extra facet, lizard skin, natural, nick, pit, polish lines, rough girdle, scratches and surface graining. Sometimes these flaws can be polished down or can be cut to remove.
Types of Diamond Inclusions
As the name suggests, this type of inclusion looks like hair or tiny feathers that extend from the girdle area into the stone and occurs during the improper diamond cutting process. A heavily bearded girdle looks grey and fuzzy as if it has been scratched. Such diamonds should be avoided as this effect detracts from a stone’s beauty.
Although diamond is the hardest naturally occurring substance on earth, it can have bruises. This flaw typically appears at a facet junction when an external force has been applied to the stone and looks like tiny root-link feathers.
The cavity is a small, slightly deep angular opening that is typically caused when a surface-reaching crystal drops out or gets removed during the polishing process. Often polishers leave the cavities as completely removing them results in weight loss which has an impact on the sale price. Be aware that such inclusions accumulate dirt and oil and become darker and more visible with time.
Chips are small, shallow openings on the surface of a diamond typically occurring at the culet, girdle edge or facet junction. They are often caused by knocks or natural wear and tear.
Chips can be easily seen with a naked eye; however, the issue with them is not only visual. Once the structural integrity of the stone has been damaged, there is a higher risk of the chip growing and spreading if subjected to further impacts. Needless to say that chips dramatically lower the value of a stone, and such diamonds are usually priced at a discount.
Pinpoint and Cloud
Pinpoints are miniscule white or black crystals embedded within a diamond. They look like tiny dots, and out of all diamond inclusions, pinpoints are considered the most benign.
Cloud is a term to define a cluster of pinpoints found very close to each other that are seen as some hazy form. It is not a big issue when clouds are small and diffused, but when they get big, they can negatively affect a diamond’s appearance and make it look hazy.
A crystal is a diamond or other mineral in its natural raw form that is embedded within the stone. Crystals are often colourless or in various shades of white; however, they can be any colour depending on the mineral present. On rare occasions, these crystals can be unique and especially beautiful when they form shapes such as a bumblebee, dolphin, heart etc.
A feather is a small fracture within a diamond’s internal structure. Depending on the viewing angle, a feather can be almost invisible or catch on to light and look like a small white feather within a diamond. Rarely feathers may have a grey or brownish colour, and they are noticeable to the naked eye.
Massive feathers can cause durability issues, especially if they reach the surface or the girdle, which is why such diamonds should be avoided.
Grain Centre and Internal Graining
The term internal graining refers to small lines, angles and curves caused by irregularities in crystal growth. Depending on its severity, internal graining can appear as creases giving a diamond milky or hazy appearance.
The grain centre is the concentrated area of crystal distortion that has a white or dark pinpoint-like appearance.
This term refers to the area that is left unpolished, meaning a portion of the rough diamond’s surface dips below a polished diamond surface. Such inclusions are mainly found near the girdle and are usually a sign of a cutter aiming to maximise the diamond yield.
Internal Laser Drilling and Laser Drill Hole
Internal laser drilling refers to the laser drilling within a diamond that creates a surface-reaching feather or expands an existing feather around a dark inclusion to reach the surface. It provides access for bleaching, which in turn decreases the visibility of the dark inclusion.
The laser drill hole is a small surface-reaching tunnel produced by the laser beam. It is usually not visible to the naked eye, but multiple laser drill holes affect the stone’s integrity and value.
The knot inclusion is a white or transparent crystal that reaches the polished diamond’s outermost surface area. It can affect the durability of the diamond and give a raised appearance.
As the name suggests, a needle is a long needle-shaped inclusion that is usually transparent or white. If in clusters, they have a dramatic effect on a diamond’s clarity grade and appearance.
A twinning wisp is a string of small pinpoints, clouds or crystals produced by an irregularity in the crystal structure. Such irregularities occur when a diamond stops growing because of unfavourable conditions and restarts growth in a different direction.
Featured image: Dmitrii Stoliarevich / Canva