What Is Gemstone Symmetry and Why Does It Matter When Buying a Diamond (or Gemstone)?

When you’re shopping for a diamond or another gemstone, you’ll probably hear a lot about the 4Cs: cut, color, clarity, and carat weight. Those four characteristics are important, but there are also smaller details that can have a surprisingly big impact on how a stone looks once it’s set in a piece of jewelry. One of those details is symmetry.

Symmetry might not sound exciting, but it plays a major role in how a gemstone interacts with light. A stone can have excellent color and clarity and still have poor light performance if the facets aren’t aligned properly. You might not immediately notice symmetry when it’s right, but when it’s off, you definitely will.

What Does Symmetry Mean in a Gemstone?

Symmetry refers to how well the different parts of a gemstone line up with one another. When a stone is cut, its facets need to be positioned at specific angles. The closer those facets are to their intended positions, the more symmetrical the finished stone tends to be. When the facets are properly aligned, the stone looks balanced, which can contribute to the flashes of light we associate with a well cut gemstone.

Symmetry applies to more than just whether the left and right sides look identical. Gemologists can also evaluate things like facet alignment, the shape of the outline, the position of the culet, and whether the various parts of the stone are properly centered.

Symmetry and the Way a Stone Sparkles

One of the biggest reasons symmetry matters is its relationship to light performance. A gemstone sparkles because light enters the stone, interacts with its facets, and is reflected back toward your eye. If those facets are positioned correctly and the stone has good proportions, it can sparkle well, but when symmetry is poor, the facet pattern may not interact with light as effectively. That can cause uneven reflections or areas that look dull.

But it’s important to understand that symmetry isn't the same thing as overall cut quality. A stone can have excellent symmetry but still have proportions that aren't ideal. A stone can have less than ideal symmetry and still be beautiful because it’s just one part of a larger picture.

Why Symmetry Is Important in Diamonds

Symmetry gets a lot of attention when you're looking at diamonds, particularly round brilliant cut diamonds. That's because they are built around a very specific facet arrangement and are expected to have an ideal visual balance. When the facets are properly aligned, the stone can produce the organized pattern of light and dark areas that contribute to the sparkle of a round brilliant cut diamond.

Although a diamond doesn't have to be perfectly symmetrical under a microscope to look beautiful to the person wearing it, it matters if any symmetry issues are significant enough to affect the stone's appearance without magnification.

Symmetry Matters in Fancy Shaped Stones, Too

Round diamonds aren't the only gemstones where symmetry matters. It can be very noticeable in fancy shapes such as oval, pear, marquise, emerald, radiant, and princess cuts. With these shapes, the overall outline of the stone becomes a major part of its appearance, so an uneven shape can be much easier to notice.

You generally want the outline to look balanced rather than having one side appear significantly wider or flatter than the other. Since fancy shapes don't follow the same symmetrical design as a round brilliant cut diamond, there is some room for individual character, but obvious unevenness can distract from the beauty of the stone.

Symmetry vs. Proportion

It's easy to lump symmetry and proportion together because they're both related to how a gemstone is cut, but they aren't the same thing. Proportion refers to the measurements of the stone, such as its depth, table, length, and width, whereas symmetry is more about how accurately those parts are aligned. A well-proportioned stone with poor symmetry may not perform the way you'd expect. This is why you should evaluate all grading characteristics instead of just focusing on a single one.

How Symmetry Is Graded

If you're looking at a diamond grading report, you may see symmetry listed as Excellent, Very Good, Good, Fair, or Poor, depending on the grading laboratory. These grades give you an idea of how closely the facets and other elements of the gemstone are aligned.

For many diamonds, especially well cut round brilliants, an Excellent or Very Good symmetry grade is generally desired. But that doesn't mean you should automatically reject a stone because it doesn't have the highest possible symmetry grade. A grading report is useful, but should never replace actually looking at the stone. That's particularly important because symmetry grades aren't necessarily a direct measurement of how beautiful a gemstone looks. A small symmetry concern might be visible under magnification but not when you're looking at the finished jewelry piece.

Can You See Poor Symmetry With the Naked Eye?

Sometimes you can, and sometimes you can't. It really depends on how significant the issue is, what shape the gemstone is, and where the asymmetry occurs. A minor symmetry issue may be nearly impossible to see without magnification, which means you certainly wouldn’t notice it when looking at a finished piece of jewelry.

More significant symmetry problems are another story. An uneven outline, an off-center culet, or misaligned facets that create noticeable dark areas change the entire personality of the stone. This is one reason it's worth looking at the gemstone in different angles and lighting conditions. If something about the shape or facet pattern looks strange to you, pay attention.

What About Symmetry in Colored Gemstones?

The conversation around symmetry isn't limited to diamonds. Colored gemstones can also benefit from good symmetry, although, depending on the opacity of the stone, it can be less important. Some colored gemstones are valued more for their color than their facet pattern, so that should be taken into consideration. A gemstone might have slightly unusual proportions and still be beautiful (and expensive) because of its exceptional color.

This is where personal preference becomes important. With a sapphire, ruby, emerald, or other colored gemstone, you may care more about color, transparency, or the uniqueness of the stone instead of whether every facet lines up perfectly.

Does Better Symmetry Mean a More Expensive Stone?

Not necessarily. A higher symmetry grade can sometimes contribute to the value of a diamond, but it isn't a simple case of better symmetry always meaning a higher price. Diamond pricing is based on a combination of factors including carat weight, color, clarity, cut quality, shape, fluorescence, proportions, and overall visual performance. Symmetry is just one piece of that puzzle.

You don't necessarily need to pay for the absolute highest symmetry grade to get a beautiful gemstone. If a stone with Very Good symmetry looks fantastic to your eye and offers a better price, it may be a much smarter purchase than spending extra money on a higher technical grade that you can't see.

Final Thoughts

Symmetry is one of those details that can be easy to overlook when you're shopping for a gemstone, but it can have a meaningful impact on the finished piece. It helps determine how balanced a stone looks and, when combined with good proportions and a quality cut, can contribute to the way it reflects and returns light.

That doesn't mean you need to obsess over finding a gemstone with a perfect symmetry grade. A technically flawless stone isn't automatically more beautiful, and a small symmetry imperfection may be completely invisible once the stone is set in a ring, pendant, or pair of earrings. When you're comparing gemstones, use symmetry as one part of the bigger picture. Look at the stone, consider its cut and proportions, pay attention to how it handles light, and decide whether you actually like what you see. After all, you're buying a gemstone to enjoy in your jewelry, not to win a grading report competition.