The Anatomy of a Diamond

To assess a diamond’s quality, most of us are taught to focus on the 4Cs of clarity, cut, color, and carat weight. But that does not cover everything you’ll see on the diamond’s certificate and certainly not what a gemologist is noticing about the subtler details of a stone. When it comes to the anatomy of a diamond, the deeper you dig, the more prepared you’ll be to make the best choice for your engagement ring.

Diamond Structure

Diamonds come in a huge variety of shapes and sizes, but all diamonds share five structural components. The way these components interact creates angles that determine how much light the diamond reflects, and thus how brilliant it appears. These five components are crucial for helping gemologists determine a diamond’s cut grading.

These are the five structural elements:

- Table, the flat, top surface of a diamond. Regardless of the diamond’s shape, it is the largest facet. The table size impacts the amount of light that can enter and reflect back in the diamond. The table refracts light rays downward as they enter the diamond, and then they’re reflected back through the table as they bounce off the pavilion.

- Girdle, the widest part of the diamond. It’s the outermost edge of the diamond where the crown and pavilion meet. Certain settings like halo[a] and bezel[b] will obscure the girdle, while others like prong[c] and channel[d] will show the girdle. A too-thick girdle adds weight to the stone in an unnecessary area, making the diamond appear smaller. A too-thin girdle results in a diamond that is more fragile and vulnerable to chipping.

- Crown, everything that sits above the girdle. Similar to the table, refracted light passes down through the crown before being reflected back up from the pavilion. The difference from the table is that the crown has multiple facets to disperse light in many directions to exhibit a diamond’s colorful fire.

- Pavilion, the area beginning at the girdle and ending at the culet where the bulk of the diamond’s weight sits. Most will focus on the size of the pavilion, but its angles are more important. An overly deep pavilion doesn’t allow enough light back up through the crown, creating a darkened effect. A shallow pavilion causes the girdle to reflect in the middle of the table creating a ‘fish-eye’ effect and overall dullness to the diamond.

- Culet, is at the bottom of the pavilion as either a point or tiny facet that lies parallel to the table. A larger culet is more likely to be visible and allows light to escape through the bottom of the stone. This effect creates a noticeably dark circle in the center of the table when viewed from the top. Small culets, or points, exhibit the most brilliance.

Diamond Symmetry

A diamond’s symmetry evaluates the symmetry of a diamond’s facets. When all the facets of a diamond are perfectly aligned, light will enter and reflect back to create maximum brilliance. If facets do not align well, shadowed spots are created by escaping light. It’s a very important factor for a diamond’s cut grade and Excellent symmetry and polish may push the cost of the diamond 10-15% higher than a diamond with Good gradings.

When gemologists are grading symmetry, they’re grading on a scale from Excellent to Poor. Symmetry is compromised when the culet and table are off-center, the girdle isn’t straight, facets are misshapen, and the crown and girdle are misaligned. Diamonds with a clarity grade of Fair or Poor are unlikely to be part of any jeweler’s inventory.

Diamond Proportions

A diamond’s proportions also help determine the cut grade given by the gemologist. Proportion measurements help to calculate four important ratios.

Depth Percentage is one of the key factors for a diamond’s cut grading. This ratio is expressed as the distance between the table to the culet and the diameter, or width, of the girdle. To optimize sparkle, depth should measure from 54% to 66%. Diamonds that fall in this range have a cut grading of Very Good or Ideal.

Table Percentage is the balance of the width of the table and the diameter of the diamond. A too-large or too-small table width in comparison to the diamond’s diameter makes the top of the diamond appear flat or rounded and will diminish sparkle. Ideal table percentage is from 53% to 70%.

Crown Angle is the angle the crown takes off of the girdle. If the crown angle is too large, sparkle will be limited. If it’s too small, the top of the diamond could look glassy. An optimal angle is between 30% to 35% and will yield the most sparkle for the stone.

Pavilion Angle is the angle the pavilion takes off the girdle. Similar to the crown angle, a too-large pavilion angle will diminish sparkle and too-shallow will make the diamond appear glassy. Cutting to maximize brilliance puts the optimal pavilion range at 42.5% to 43.5%.

Diamond Fluorescence

Almost a third of all diamonds naturally emit a glow under ultraviolet light, a phenomenon called fluorescence. We delve deep into fluorescence in our guide, but it’s important to know that although fluorescence does get a grading on the gemstone certificate, it has a negligible effect on the appearance of a diamond.

The majority of diamonds with fluorescence exhibit a blue tone under UV light, but other colors like yellow, orange, red and green have been seen. In some instances the blue fluorescence can balance out a stronger yellow tone in a diamond, making lower color grades appear higher than they really are.

Diamonds graded as having no fluorescence are priced at a premium because this feature is often presented as a defect in the diamond. But fluorescence is not visible in natural light. Putting more of your budget toward a better cut and clarity that affects the visual appearance of the diamond more will be the better investment.

Diamond Inclusions & Blemishes

As you may know about the clarity of a diamond, this grading is based on the visibility and volume of inclusions and blemishes. A natural occurrence, an inclusion is a flaw within the diamond and a blemish is an imperfection on the stone’s surface. There are many different types of inclusions and blemishes, and each will have a different effect on the diamond.

A cavity is a hole in the surface of the diamond. It can be found in different sizes and locations across the stone and can impact the overall durability of the diamond if it’s in certain locations. If there’s a cavity on the table, it will be very apparent once it’s set in jewelry.

A chip is a shallow indentation in the surface of the stone. These are sometimes created during the cutting of a diamond. If the chip is located at the edge of the diamond, it’s possible to set the stone so that the chip isn’t visible.

Clouds are groupings of miniscule inclusions that are indistinguishable from one another, even when viewed under magnification. These inclusions generally do not affect the clarity grade because they appear as a translucent cloud so cannot be seen by the naked eye.

A crystal is the name for the presence of another mineral being included within the larger structure of the diamond. Crystals are documented in a variety of sizes, colors, and locations, so if they’re colorful and visible, a crystal could affect the clarity and value of a diamond.

Feathering is a fissure within a diamond that was likely created as the diamond was first forming in the earth’s crust billions of years ago. If located towards the edge, prong placement can easily hide it, but they may be noticeable elsewhere. They can affect durability if too close to the girdle or they create an opening to the surface of the stone.

A knot is a diamond crystal inclusion that breaks through to the surface of the stone. It’s possible for the knot to be raised above the rest of its facet and depending on the size, you may be able to feel it as you run your finger across it.

A natural is an unpolished part of the diamond and is usually found on or around the girdle. If this blemish travels to the crown or pavilion, it’s considered an indented natural. These do not affect the overall quality or durability of the stone and are generally appreciated as a remnant of the diamond’s natural growth.

A needle is similar to a feather inclusion but appears as one very narrow, elongated line. Their length varies, so some can be more visible. And since they’re white or transparent, they don’t typically affect the light return of a diamond.

A pinpoint inclusion is a tiny speck of organic matter within a diamond. They are usually only detectable under high magnification and do not affect the durability of the stone. Typically, the presence of a pinpoint inclusion will decide whether a diamond receives a VVS1 or IF clarity grade.

Twinning wisps are the result of growth defects within the diamond’s crystalline structure. They are formed by different inclusions twisting together and are most common in fancy cut diamonds. Twinning wisps are generally more noticeable than other inclusions.

person inspecting a diamond

Diamond Polish

After a diamond is cut, it is polished to have a smooth finish. Polishing improves the sparkle of a diamond and is accomplished by a mechanized wheel that buffs every facet. During polishing, the wheel can leave miniscule scratches on a diamond’s surface. If the scratches are substantial enough, they may be able to misdirect light as it travels through the diamond.

Practically every diamond has small remnants of polishing marks on its surface, and a gemologist will evaluate if these create a defect in the diamond’s appearance. And while this may seem like a clarity concern, polish is graded separately from clarity. While polish will have a relatively small effect on the overall look of a diamond, it’s best to stick with a grading from Excellent to Good.

Buying a diamond can feel like a daunting decision. We hope that this information covering the anatomy of a diamond can help you make the most confident choice for your diamond engagement ring. And if you still have questions, we’re here to help.

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