Understanding Color Phenomena in Colored Gemstones

5 minute read

Prized for centuries for their rarity and revered for their rainbow of hues, colored gemstones have long rivalled diamonds as the world’s greatest natural treasures. From their color, symmetry, and surface appearance, every gemstone is unique with its own aesthetic appeal. The greatest source of a gem’s beauty and allure, however, has always been its color. Luckily, the natural variety and uniqueness of precious gemstones ensures a color can be found to fit any taste and setting.

Pink Sapphire drop earrings that display a vivid, highly saturated color Pink Sapphire drop earrings that display a vivid, highly saturated color

Tanzanite, Tourmaline, Ruby, Sapphire, Emerald – the list is endless. Colored gemstones have long enjoyed a vast history that illuminates their importance and wide variety of uses. Historically, colored stones have been a staple fixture in jewelry across cultures and continents. Poets and artists alike have used images of the colored stones as vehicles to express love, passion, and power. In certain cultures, colored gemstones such as sapphires were worn as protection. In others, rubies acted as commanding symbols of wisdom and beauty. With legendary histories, it’s no surprise that colored gemstones have reached legendary heights in recent years in both value and reputation.

How exactly did the captivating colors of gemstones come to be? What is the best way to explain these fascinating and wide-ranging colors? Read more to learn how.

Distinguishing Different Gemstones

2,000 years ago, students classified gems based on color appearance alone. Using this method, students concluded that ruby and red spinel were in fact the same gemstone. Today, however, we know these crimson stones belong to entirely different families. Prompted by advances in technology, gemologists began to understand the different mineral make-ups of colored gemstones, and thus began to classify gemstones in an entirely new way. Realizing that each colored gemstone contained a different chemical formula, gemologists separated gemstones into different species and, within each species, different varieties.

30-5688_1 When the trace element chromium is present in the corundum species, the gemstone is considered a ruby

It’s important to note that for colored gemstones no chemical composition is absolutely pure, and every gem contains at least a few atoms that aren’t part of the normal chemical formula. These atoms are called trace elements, and they are responsible for giving variety to the gem’s color. For instance, Corundum, the gemstone species of both sapphires and rubies, is comprised of two atoms of aluminum and three atoms of oxygen. However, when the trace element of chromium is present, the ruby acquires its red color and becomes vastly different from the sapphire. It’s these natural variations that contribute to the plethora of colored gemstones known today.

How Color Occurs

The color that an observer sees in a gemstone is born from an interaction between light, the gemstone, and the observer. Light, although seemingly white, is a combination of all the colors of the spectrum, and each color represents different energies. Because of these different energies, some light waves are absorbed more fully by the gemstone through a process called selective absorption. Importantly, it’s the light waves that aren’t absorbed - in other words returned - that determine the color the observer sees.

It is the gem’s chemical composition and crystal structure that ultimately affects the way it absorbs and returns light. Because each species and variety contains a different mix of chemicals (such as the chromium presence in the ruby gemstone) each crystal structure is unique.

Describing Color

Three key terms are most commonly used when identifying and describing colored gemstones: hue, tone, and saturation.

While discussing color, start with describing your first impression of the gemstone’s basic body color—the hue of the gemstone. Next, delve into the specifics of that basic color, including its relative degree or darkness or lightness. This is known as the stone’s tone, which helps specify the specific stone in question. Finally, note how strong or light the stone’s color appears. This is its saturation. Highly saturated colored gemstones, such as Bubblegum Pink Sapphires, will often appear vivid and intense.

A 4.10-carat purple sapphire that displays a remarkably deep tone and vivid saturation A 4.10-carat purple sapphire that displays a remarkably deep tone and vivid saturation

Other Important Color Aspects

In each gemstone variety there exists a color range, and certain colors within that range are more desirable than others. Emeralds, for example, constitute green hues anywhere from light to dark and vivid. The fine color of a color range, however, is typically the color most preferred out of the color range by the jewelry industry and consumers. Generally speaking, the fine color is often the darkest tone with the highest level of saturation.

A gemstone’s growth is never completely even and smooth. During the development of a gem, its often inevitable that certain parts of a stone receive greater or lesser amounts of color-causing nutrients. In turn, this causes the gemstone to display bands of slightly different colors - an effect called color zoning. Like most aspects in the colored gemstone industry, this can enhance or spoil a gemstone’s appearance and overall stability.

Interestingly, certain gemstones display pleochroism, or the ability to display different colors from various viewing angles. Stemming from the Greek word, “having many colors,” different varieties of gemstones can display perchloric capabilities. Tanzanites, for example, are most noted for this characteristics and can be easily observed by the naked eye. From some angles, a tanzanite’s basic body color can appear deep violet, while from others it can appear to be a deeper purple. Other gem varieties that possess this capability are tourmalines and kunzite.

Tanzanites can often display pleochroism, or the ability to show different body colors from various viewing angles Tanzanites can often display pleochroism, or the ability to show different body colors from various viewing angles

In the end, choosing a colored stone is a matter of personal preference. Throughout the ages, fades and fashions have risen and fallen, but the beauty of these stones still endures. With an endless variety of hues to choose from, anyone can find the perfect gemstone for their collection.

Click here to view our current selection of colored gemstones.

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