Turquoise is a popular gemstone known for its striking blue-green color. But there has long been debate over whether turquoise should be considered blue or green. The answer lies in turquoise’s unique chemical composition and how the human eye perceives color. This article will examine the evidence to determine whether real turquoise is scientifically green or blue.
The Composition and Cause of Turquoise’s Color
Turquoise gets its characteristic color from its chemical makeup. Turquoise consists of hydrated copper aluminum phosphate, commonly called CuAl6(PO4)4(OH)8·4H2O. The copper provides the blue color, while the aluminum and phosphorus provide the green. The exact hue of a turquoise specimen depends on the relative amounts of these elements. More copper leads to a deeper blue, while more aluminum and phosphorus result in a greener tone.
This combination of blue and green elements is why turquoise can appear to shift between blue and green depending on the light conditions. This property is known as metamerism. The perception of color is subjective and can vary based on the type of light source. Under natural daylight conditions, which have a higher color temperature, turquoise generally looks greener. Under incandescent bulbs, which have a lower color temperature, turquoise tends to appear more blue.
How the Human Eye Perceives Color
The debate over turquoise’s color also comes down to the biology of human color vision. Human eyes have special receptor cells called cone cells that detect different wavelengths of light. There are three types of cone cells, each responsive to different colors:
| Cone cell type | Color detected |
|---|---|
| S cones (short wavelength) | Blue light |
| M cones (medium wavelength) | Green light |
| L cones (long wavelength) | Red light |
The brain processes the relative stimulation of these cone cells to produce our perception of color. Turquoise stimulates both the blue-detecting S cones and the green-detecting M cones fairly equally. Since there is no dominant cone signal, the brain has difficulty classifying turquoise neatly into either the blue or green color categories. This gives turquoise its subjective, changeable appearance.
Color Science Classifications
Color scientists who study human vision have classified turquoise as green based on precise measurements of its light spectrum. While turquoise stimulates both S and M cones, spectral analysis shows that it tends to stimulate M cones slightly more than S cones. Green has a wavelength of about 500-565 nm, while blue wavelengths are around 435-500 nm. Natural turquoise’s wavelengths usually fall right in the middle of the green range.
This lines up with analytical color models used in printing and design, like the CMYK and RGB models. In these models, turquoise is reproduced by combining larger amounts of the green pigments/light rather than the blue:
| Color Model | Turquoise mixture |
|---|---|
| CMYK (cyan, magenta, yellow, black) | Mainly cyan + smaller amounts of magenta and yellow |
| RGB (red, green, blue) | More green value than blue value |
These technical definitions place turquoise firmly on the green side of the color spectrum.
Common Language Classifications
Everyday usage of color terms, however, relies more on mental perception rather than technical specifications. And the mental perception of turquoise differs greatly between individuals. Some common ways turquoise is described:
| Description | Classification |
|---|---|
| Blue-green | Turquoise is neither pure blue nor pure green |
| Greenish blue | Closer to green but still has blue tones |
| Bluish green | Closer to blue but still has green tones |
Regional and cultural differences also affect how turquoise is categorized. For example, in Persian culture, turquoise has traditionally been classified as blue. In Chinese culture, it is considered a shade of green.
The vagueness and subjectivity of human color perception is why turquoise has no universal classification in everyday language. Its color can only be described relative to the perceiver using terms like “greenish” or “bluish.”
Turquoise Gemstones – Natural vs. Treated
When discussing the color of turquoise, it is also important to distinguish between natural untreated turquoise and treated turquoise. Most turquoise used in jewelry today has been artificially enhanced to improve the color.
Natural turquoise rarely occurs in the uniform vibrant blue-green shades that are desirable in jewelry. Natural turquoise untouched by treatments usually looks more pale green to dark green:
| Natural Turquoise Color Range |
|---|
|
Treatments like dyeing and impregnation can shift the color closer to an ideal uniform greenish blue:
| Treated Turquoise Color Range |
|---|
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So while scientifically turquoise is considered a shade of green, commercially enhanced turquoise is often made to look more blue. This means most turquoise jewelry is marketed as “blue turquoise” even though unmodified turquoise is greener.
Conclusion
While there is no unanimous agreement, turquoise is considered green according to color science and spectral analysis. This classification is based on precise measurement of light wavelengths and wavelengths are predominantly what visual systems respond to. However, common perception is more complex, subjective and culturally defined. The balance between blue and green cone cell stimulation makes turquoise appear changeable between greenish blue and bluish green. So turquoise is best described as a color “in between” blue and green rather than definitively one or the other. When shopping for untreated natural turquoise, expect to see more greenish hues. For commercial quality turquoise that appears vivid blue-green, it has likely been treated to enhance the blue tones. So in summary, real turquoise is technically green, but can appear somewhat blue or green depending on the specimen and the beholder’s visual system.
