Diamond Anatomy & 4C

Diamond Formation

Diamond’s characteristic chemical composition and crystal structure make it a unique member of the mineral kingdom.

Diamond is the only gem made of a single element: It is typically about 99.95 percent carbon. The other 0.05 percent can include one or more trace elements, which are atoms that aren’t part of the diamond’s essential chemistry. Some trace elements can influence its color or crystal shape.

The way a mineral forms helps determine its identity. Diamond forms under high temperature and pressure conditions that exist only within a depth range of about 100 miles beneath the earth’s surface. Diamond’s crystal structure consists the carbon atoms that are bonded in essentially the same way in all directions. The result is  diamond is so hard that you can only scratch it with another diamond.

Without any one of these factors, diamond might be just another mineral. Fortunately, though, this special combination of chemical composition, crystal structure, and formation process gives diamonds the qualities that make them extraordinary.

On almost all modern birthstone lists, diamond is recognized today as the birthstone for April.

Diamond Anatomy 

When you’re shopping for a diamond, its brightness and sparkle will draw you to the jewelry counter, and keep you captivated long after you’ve made your diamond purchase. Achieving maximum brightness and sparkle requires excellent cutting technique, which is reflected in the diamond’s cut grade. Of the 4Cs, no other ‘C’ has more impact on a diamond’s appearance.

When people think of “cut,” they often think of the shape of a diamond rather than its cut quality. Cut is all about a diamond’s fire, sparkle, and brightness, and as a value factor, it refers to a diamond’s proportions, symmetry and polish; those factors that determine the cut quality or the fourth ‘C.’

A number of complex factors are considered when evaluating a diamond’s cut grade: its proportions, the symmetry of its facet arrangements, and the quality of its polish or finish. The cut grade reflects the diamonds appearance.

Table Size: The table is the top horizontal facet of the diamond. The average table size is expressed as a percentage of the diamond’s average girdle diameter. While an ‘Excellent’ grade diamond will have a table size between 52 and 62 percent, other proportions are important too.

Total Depth: The diamond’s overall depth from the surface of the table to the culet, expressed as a percentage of the average girdle diameter.

Pavilion Depth: The pavilion is the lower portion of a diamond from the bottom edge of the girdle to the culet. The pavilion depth is expressed as a percentage of the average girdle diameter. A pavilion depth that’s too shallow or too deep will allow light to escape from the side or bottom of the stone. A well-cut diamond will direct more light upward through the crown.

Pavilion Angle: Pavilion angle is another important dimension of the stone, especially as it relates to a diamond’s brightness. It is the average of the angles formed by the diamond’s pavilion main facets and its girdle plane. This should fall between 40.6 and 41.8 degrees to be considered “Excellent,” providing other parameters also fit their proper ranges.

Crown Height: The crown is the upper portion of the diamond, from the top edge of the girdle to the table. The average crown height is expressed as a percentage of the average girdle diameter. It can affect both the dispersion and brightness of a diamond.

Crown Angle: The crown angle is the angle that’s formed where the bezel facets meet the girdle plane. The crown angle in a well-cut diamond will be within 31.5 to 36.5 degrees. The crown angle has a large effect on the face-up appearance of a round brilliant cut diamond. The best range of crown angles provide a route for exiting light dispersion, as well as additional contrasting directions for entering light.

Star Length: The horizontally projected distance from the point of the star facet to the edge of the table, relative to the distance between the table edge and the girdle edge. A well-cut diamond will range between 40 to 70 percent, when other parameters are within the correct ranges.

Girdle Thickness: The girdle is the middle portion of a diamond, a narrow section separating the crown from the pavilion, and functions as the diamond’s setting edge. The girdle thickness is described as a range from its thinnest to thickest areas. A thick girdle is less desirable because it unnecessarily adds weight to the stone where it matters the least (making the diamond appear smaller). An extremely thin girdle is sometimes referred to as a knife-edge, and results in a diamond that is more fragile and susceptible to chipping. Therefore, a girdle that is “medium to slightly thick” is preferred.

Lower Girdle / Half Facet Length: This ratio is measured by calculating how long the lower girdle facets are relative to the length of the pavilion. This defines the contrast of a round brilliant cut diamond, which controls the brilliance of a diamond. The well-cut diamond will range between 65 to 90 percent. Diamonds with longer lower half facets will have a little more scintillation.

Culet: The culet is the small facet at the bottom of a diamond intended to prevent chipping and abrasion to the point. The culet size can affect face-up appearance and it’s described as the average width of the facet. Size is expressed as none, very small, small, medium, slightly large, large, very large, and extremely large. When there is no culet, it is sometimes referred to as a pointed culet. Preferably the culet will not be visible with the unaided eye, and when described as none (no culet), it falls in the excellent range.

4C – Carat, Clarity, Cut, Colour

CARAT (ct.)

Diamonds are sold by the carat (shown as ct.), which is actually a unit of weight, though most think of a carat in terms of size. The word “carat” comes from the “carob” seed, the original unit of measure for diamond traders. Today, a carat is equal to exactly 0.2 grams (about the weight of a paper clip). Carat weight is unrelated to the similar sounding karat, which refers to gold’s purity.

Two diamonds of equal carat weight can have very different costs based on other factors (such as cut, color, and clarity). In understanding the importance of carat weight, know thy partner. If the recipient’s heart is set on a certain size diamond, then carat weight will probably be the most important factor in your search until the desired size is attained. At that point, other criteria will take on more importance. Most women can tell you the carat weight and shape of their ideal diamond, and most men can tell you the price.

As the carat size of a diamond increases, the diamond’s price increases at an increasing rate. Why? Because the larger the diamond, the more increasingly rare it is. Fewer than one in one million mined rough stones are large enough to produce a finished 1 carat diamond.

It’s important to note that a diamond’s carat weight does not equal size. Because of differences in depth and cut, two diamonds with identical diameters may in fact be two completely different sizes. Therefore, it is possible to buy a diamond that looks bigger than another that may actually have a smaller carat weight. When buying a diamond, consider the length, width and depth of a stone as well as the surface of the diamond (the part that will actually show when the diamond is set).


A flawless diamond with little to no imperfections is often desired due to its rarity, but they are also the most costly. Therefore, it is important to keep in mind that it is very common for diamonds to be formed with slight imperfections.

These imperfections are known as “inclusions” and usually occur during the diamond’s crystallization period within the earth, or from the stresses of mining and processing. Inclusions are anything from tiny white points to dark dots, cracks or scratches. The fewer inclusions, the more valuable a stone is. Clarity is evaluated using a 10‐power magnification. This means that the object viewed appears 10 times its actual size. The diamond grader examines the clarity characteristics with respect to the nature and number of characteristics, as well as their size, color and position.


There are six main diamond clarity grades (see above chart). The top one is called Flawless (denoted by “FL”), followed by the next best grade, Internally Flawless (IF).

Two diamonds

The main difference between VVS and VS clarity is the size of inclusions.

VVS (Very, Very Slightly Included) and VS (Very Slightly Included) are the next two grading ranges. (You should remember that VVS denotes higher quality than VS.)

The bottom two grades on the scale are Slightly Included (SI) and Included (I).

What Is VVS Clarity?

Diamonds of VVS clarity have very slight imperfections that even trained professionals cannot easily see with a loupe or microscope.

The VVS grading range is divided into two sub-grades: VVS1 and VVS2, with VVS1 being the higher grade.

What Is VS Clarity?

VS-clarity diamonds have inclusions that are usually hard to see under 10x magnification. A small number of these imperfections may be more readily visible, but they are still tiny. Like VVS clarity, the VS grade is divided into VS1 and VS2.

VVS Diamonds Have Smaller Inclusions

The main difference between VVS and VS clarity is the size of inclusions: VVS diamonds have smaller and less visible flaws. Usually, even when you look at these stones under a microscope, it is hard to make out any inclusions.

 VS diamonds, on the other hand, will have some inclusions that will be easy to spot under magnification. Most of the flaws will still be microscopic, but at least one or two of them will be bigger and easily visible with a jeweler’s loupe. Keep in mind that we are still talking about inclusions that are not visible with the naked eye.

A superior cut or color can make a VS diamond more expensive than a VVS stone, so you should also evaluate other quality characteristics. But all else being equal, in terms of affordability, VS clarity is the clear winner.

Remember that the differences between VS and VVS are only detectable using a microscope or a 10x loupe. You won’t be able to distinguish them with the naked eye.


People often use the words “cut” and “shape” interchangeably when talking about diamonds. However, these two terms have slightly different meanings. Shape refers to the general outline of a stone.

On the other hand, although a specific cut implies a certain shape, the term cut technically refers to the number, arrangement, shape, and proportions of a stone’s facets. A diamond’s shape tells you how a stone looks, whereas its cut gives you information as to how this shape has been achieved through cutting.

Technically, two diamonds may have the same or similar shapes, but their cuts will be considered different if their facets are arranged or shaped differently.

Ideal Cut 

Although there are a number of diamond cuts available in the market, here are the ones you are most likely to see when shopping for jewelry:

Round Cut

The round cut is perhaps the most popular diamond cut sold today. This is the cut that is specifically designed to maximize brilliance, and for this reason, flaws and yellow tints in round-cut diamonds are less visible than in stones of other cuts. Many consumers consider the round cut the classic diamond cut.

Princess Cut 

The princess cut is similar to the round cut in that both are brilliant cuts, but the princess cut has a rectangular outline instead of a round one. Although not as brilliant as the round cut, the princess cut is a good alternative to it if you are looking for a diamond that has a square or rectangular shape while exhibiting a good amount of sparkle.

Emerald and Asscher Cuts

The emerald cut is a rectangular step cut with trimmed corners, and its square variation is called “Asscher cut.”The emerald and Asscher cuts differ only in outline, but the shape and arrangement of their facets are the same. These cuts do not have as much brilliance as the round or princess cuts, and thus any imperfections or color tints in the emerald and Asscher cuts are more visible.

Cushion Cut

Cushion-cut diamonds look rectangular or square, but their corners are rounded, making the stone’s shape look like a pillow. The cushion cut belongs to the group of brilliant cuts.

Radiant Cut

The radiant cut has a rectangular or square shape with truncated corners. This is yet another brilliant cut, and it is often compared to the cushion cut. The radiant cut has some features that are characteristic of the emerald cut, and this commonality leads some people to classify the radiant cut as a mixed cut.

Oval Cut

The oval cut is another brilliant diamond cut and can be viewed as a modified version of the round cut. An oval-cut diamond is a good choice if you want your piece of jewelry to create the impression of length, especially if the stone is mounted in a ring.

Marquise Cut

Marquise-cut diamonds have an oval-looking outline, but they have two pointed ends.These sharp points are especially vulnerable to chipping and should be protected properly by the setting when the diamond is mounted in a piece of jewelry.

Pear Cut

The pear cut has an oval-looking shape, and one of its ends is pointed, making this cut’s outline look like a drop or a pear. Pear cuts combine features of the marquise cut and the oval cut. If you have a pear-shaped diamond, make sure its sharp end is protected when set in a piece of jewelry.

Heart Cut

The heart cut looks very similar to the pear cut, but the rounded end of a heart-shaped diamond has a cleft. If you are buying a heart-cut diamond, make sure its left and right parts are symmetrical.

Trilliant Cut (Trillion Cut)

The trilliant (or trillion) cut has a triangular outline. Its ends can be pointed or rounded, and if they are sharp, they will be vulnerable to chipping, so they should be protected accordingly when worn. Trilliant-cut diamonds are often used as side stones, but they can also be worn as center diamonds.