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What Determines the Value of a Colored Gemstone?

Posted by Catherine Claus on


The true worth of a gemstone can only be measured by its owner. Even a humble stone can hold priceless value when it carries memories and meaning. And when you think of gems as snapshots of ancient geological history, each and every one is precious.

But alas, appraisers must assign a value, or price per carat, to each gemstone. To determine the monetary worth of an emerald, ruby, or sapphire, multiple factors are considered.

The Four C’s of Colored Gemstones

Affectionately known as the Four C's to us gem nerds, Carat, Clarity, Color, and Cut are the four yardsticks used to measure gemstone value. Whether you plan to buy one gem or begin a collection, it is worth your while to understand how each of these factors affect your investment.

While the Four C's are well established when it comes to grading precious stones such as diamonds, their application to fine colored gems is a little more complex. For example, color, just one of the four factors, has four elements of its own: hue, saturation, tone, and coverage.

Let’s take a closer look at how the Four C’s are applied to colored gemstones. 

Carat

The size of a gemstone is generally measured by weight in metric carats (one carat is equal to 1/5th of a gram). While gems of a higher carat are often more highly valued, the other three Cs each have a significant role to play. For example, if a gem displays excellent clarity and color, the value does not simply increase linearly with the carat, but instead rises exponentially.

Clarity

Clarity refers to a gem’s degree of transparency. Precious rocks that contain cloudiness or other visible markings within are said to have inclusions, while stones with markings on their surfaces are described as blemished. Inclusions and blemishes can often add character to a gem, giving it a unique fingerprint.

These interruptions in clarity can affect the visual appeal of a gemstone, as well as its durability. That’s why, in most cases, gems are valued higher when they are glassy and utterly transparent. But it’s not always that simple.

Cosmetic inclusions do not always mean lower quality. Some precious stones actually increase in value due to their inclusions. Star sapphire, for example, derives both its value and its name from its needle-like inclusions.

Color

Color is, by most accounts, the most important factor in determining the value of colored stones. It’s also the most complex. As I mentioned earlier, the color of a gemstone is composed of four elements:
  1. Hue: The name of the color, like red or pink.
  2. Saturation: The color’s vividness or brightness.
  3. Tone: The depth of color (or lack thereof)
  4. Coverage: The color’s consistency

The interplay between hue, saturation, and tone produces the color, and coverage refers to the evenness of that color throughout the gemstone.

Almost all colored stones are assessed principally by their color. In fact, certain colors determine the actual classification of a gem! For instance, rubies and sapphires have similar chemical compositions, but we distinguish them due to their difference in color.

Cut

A high quality cut takes the other three C’s into account and enhances a gemstone’s best features. The best stone cutters bring an artful eye and practiced attention to detail to their craft. 


Balancing carat, clarity, and color when cutting a gem is known as the "cutter's tradeoff" because it often means preserving one quality at the expense of another. For instance, cutting an alexandrite to display the best color means sacrificing carat, and conversely, preserving carat instead of removing an inclusion may result in less clarity.

Conscience: The 5th C at Thesis Gems

In addition to the Four Cs, there are other factors that can affect the value of a gem, including country of origin and whether the gem has been artificially enhanced. Knowing the provenance of a gem inherently increases its value, and will help understand how it was mined and if it was done so ethically.

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At Thesis Gems, it is a part of our core mission to support people, their workmanship, and natural resources. Knowing where our precious gems and metals have originated, and knowing that they have been sourced responsibly is essential to understanding the true value of any gem.

If you're curious about collecting with a conscience, please don't hesitate to contact me today.