Gemstones are one of those creations of nature that never fail to amaze us with their mesmerizing looks and unique properties. However, recent discoveries have revealed some powerful features in their structure that result in fascinating effects. Different stones exhibit different optical effects one of which is the phenomenon of color change.
There are many gems that, when exposed to different lighting conditions, appear different in colors. Color changing gemstones have acquired a lot of interest from gem lovers and collectors across the world. In this guide, let us try to know some of these color-changing stones better and understand the reason behind this effect in different gemstones.
What is Color Change in Gemstones?
Collectors often have a special fascination for gemstones that exhibit unique optical properties and effects. Some gems possess specific structures or traits that result in a color change under different conditions. Some of these can appear vivid in color when seen from one angle while appearing pale from another. Many gemstones tend to change color in response to the source of light under which they are observed.
Color changing gemstones are some of the most unique and rare stones existing on the planet. They are highly appreciated for their varying nature characterized by different colors when interacting with different types of lighting conditions. Such a phenomenon is unusual and can range from a subtle change in hue to an extremely dramatic effect.
It is, however, important to differentiate color change from a color shift. Many gemstones display some level of shift in color under varying lighting conditions. For example, blue sapphire appears to be stronger blue under natural lighting as compared to artificial light sources because natural sunlight has more blue wavelengths. On the other hand, ruby gets an enhanced color under incandescent light as it is richer in frequencies corresponding to yellow and red components of the light spectrum.
Color change in gemstones should also be distinguished from stones that exhibit varying colors from different angles under the same source of light. Tourmaline and other gemstones are pleochroic and display such a property. However, the color change feature in gems is a more pronounced change as compared to color shift as they only show a change when there is a change in the quality of lighting.
What Causes Color Change in Gemstones?
The phenomenon of color change observed in some gemstones attributes to the properties of the crystal lattice of the gem. A stone looks blue because it absorbs all color frequencies and reflects back the blue color. When a gem has low absorption in certain parts of the spectrum, it is known as the transmission window.
Some gemstones have multiple similar-sized transmission windows so they show a color change when there is a change in lighting. This means a stone that can absorb the frequencies except red and green appears red when the light is rich in red wavelengths and green when it is rich in green wavelengths.
For color changing gemstones, a change in light settings changes the colors we can see. Natural sunlight is rich in green and blue wavelengths and has less red light whereas incandescent light has a redder wavelength and lesser green and blue. This is why a blue sapphire, when observed in sunlight, looks blue but looks different when seen under incandescent lighting. It appears deep violet or red depending on the wavelength of the light used for viewing the gem.
Top Color Changing Gemstones You Should Know
Let us try and learn more about some of the most popular families of gemstones that exhibit the stunning color change effect.
Alexandrite
The gemstone after which the color changing effect in gems is named, Alexandrite is known to be the most expensive in the world. It can exhibit a color change ranging from bluish mossy green in natural light to a prominent shade of red with a raspberry hint. It also changes from an emerald green hue in light to complete red in the dark. This is why gemstone enthusiasts refer to this stone as ‘Emerald by Day and Ruby by Night’.
A few of the rarest of these are even seen showing a blue hue in natural light which changes to purple indoors. The gem was discovered back in 1830 and was originally named ‘diaphanite’ meaning ‘two appearances’ which later came to be known as Alexandrite after the Czar of Russia. Mineralogists believed it to be emerald until it stunned them by looking purple-red under an incandescent lamp.
Alexandrite belongs to the Chrysoberyl family of minerals and gets its color changing property from the unique chemical composition. The effect is seen in specimens where aluminum is replaced with chromium in the atomic structure. The formation of this stone also requires beryllium but it is quite rare to find beryllium and chromium in the same rock together. This is why Alexandrite is so rare and there are only a handful of deposits in the world.
Some varieties of Alexandrite exhibit the effect called pleochroism whereby you can see different hues from different angles, particularly under polarized light. Such an effect is not so distinctive as the color change effect. This gemstone is trichroic which means it can exhibit three colors (red, green, yellow-orange) based on the angle you are viewing it from.
As this color changing gemstone can form only in a specific situation, it is quite rare, special, and highly valued. Large stones with strong color change and high clarity are priced higher because they are the rarest and highly sought-after. Stones over five carats are extremely rare. Some of the popular sources of Alexandrite include Brazil, Sri Lanka, and the Ural Mountains of Russia.
Sapphire
Sapphires are some of the most appreciated gemstones that come in different colors with varying rarity and value. However, the most valuable is the deep, royal blue-colored gem that is saturated yet transparent. Gemstone and jewelry fascinates are knowledgeable about sapphires as they hold great significance among historical and royal figures. People born in September are specifically fond of wearing this gem.
Color changing sapphires are one of the rarest varieties of this gemstone. The color change is generally seen from blue in natural light to purple shades under a lamp. Some varieties of this stone look grey-green in natural light and turn pink to reddish-violet when viewed under incandescent light. The optical property can be seen in sapphires sourced from around the world though the most recent specimens come from Tanzania and Madagascar.
The color change in this gem is attributed to traces of metal present in it. For the blue color changing sapphire, a mix of titanium, iron, and chromium create distinct hues under different lighting conditions. While titanium and iron give the stone its blue color, chromium is the metal responsible for the red color of rubies and gives sapphire the ability to showcase a shift in color. It is the way these minerals interact with the light spectrum that enables the gemstone to display different colors.
The optical effect in sapphires is the same as that seen in alexandrite. When seen under fluorescent lighting, it gets exposed to a bigger spectrum of wavelengths. Incandescent lighting is not so rich in blue wavelengths so you can see hues of red when seen under such a light. The rare color changing sapphires are prized by gem and jewelry collectors; the ones exhibiting strong color change and having a nice clarity and cut are prized the most. Sapphires displaying bi-coloration sell for even more.
Garnet
The garnet gemstone is known for its alluring appearance throughout the world. However, it has an interesting green kiwi-like color and a color changing property that set it apart. Garnets can change their color based on the lighting used to view them. The change in color can range from vibrant greens and deep red hues of orange and brown to subtle tones of purple and pink.
This color changing gem is believed to have this characteristic to protect its owner in the darkness of night and is one reason why travelers wear it. The most famous of this variety was discovered in the 1990s, the pyrope-spessartine which changed its tone from blueish green to purple based on the warmth or coolness of the lighting. The color change is associated with high proportions of the metallic element vanadium.
The gem’s hardness, color variety, and clarity make it a popular choice for jewelry. Garnets can be found in red color which is likely to get confused with rubies. Color changing variety is the rarest of this stone and the value depends on its qualities and color among other factors. The change of color from blue to purple is quite rare. A 4.2-carat blue color changing garnet fetched about $7 million in 2003.
Tsavorite is another valuable garnet that became recently popular in jewelry. It is famous for its vivid green appearance. Garnets are found in several areas around the world, the biggest sources being Sri Lanka, Africa, and Russia.
Diaspore
A very rare variety of gemstones, Diaspore has an outstanding color changing feature as it can display up to three distinct colors under different lighting. The optical effect it shows is known to emit various bands of colors, particularly when viewed from different angles. The gem was discovered in Turkey in the 1970s and was given the name after the Greek word ‘diaspora’ meaning ‘to scatter’ describing its unique color effect.
‘Zultanite’ and ‘Csarite’ are the trade names given to the color changing variety found in a privately-owned mine in Turkey known for its finest quality mineral. This gem naturally occurs as a yellow, green, or brown-colored mineral that changes from brownish green in natural light to champagne or even pink under incandescent lighting. The optical effect is more noticeable in gems larger than five carats.
The hardness of diaspore gemstone is around 6.5-7 on the Mohs scale which makes it quite durable. Moreover, it can split quite easily, meaning you need to wear it with caution as a piece of jewelry. Go with a gem that is properly cut and graded to lower the risk of splitting. This stone can even show a cat’s eye effect or chatoyancy which is seen as a single light band across the surface.
Talking about its value and rarity, high-carat Zultanite has a lot of demand and value. Diaspore is not so uncommon and can be found across the world though high-carat ones are rare and found abundantly only in Turkey. The bigger of these stones exhibit an exceptional color effect. However, it is important to identify the real stone as many fakes are sold under the name. A real Zultanite comes with a certificate of authenticity. Its artificial counterpart is colorful in appearance but doesn’t show the genuine color change effect.
Fluorite
This gemstone is popular for its alluring optical properties. It is known to be one of the most fluorescent stones though it is not commonly used in jewelry because of its inappropriate hardness. It shows a fascinating glow in bright violet-blue under ultraviolet light.
The gem has such a strong fluorescence that it is one of the few to display the effect in natural sunlight. Ruby is another stone exhibiting this effect. Color changing fluorite did not appear in the market until recently. It remains more popular with collectors than jewelry enthusiasts. The value and price of this gem vary depending on the quality and size as well as other optical properties.
Andesine
Another rare color changing gemstone from Tibet and Mongolia, Andesine exists in shades of yellow, green, and red and belongs to the feldspar family of minerals. The gem exhibits different hues under different lighting conditions and can be seen in deep green, vivid violet, or other colors.
Final Thoughts
Color changing gemstones are rare, valuable stones considered to be an asset for the jewelry industry across the globe because of their outstanding beauty and optical effect. While there are several varieties of gems exhibiting beautiful color change, Alexandrite and Sapphires remain the most valuable and rare and fetch a higher price as compared to their normal counterparts.
Alexandrite is, in fact, considered to be the rarest and the most significant of all color changing gemstones to an extent that any stone displaying this characteristic is labeled to have the ‘Alexandrite’ effect, making it a measure of strength and quality of the phenomenon exhibited by these precious, beautiful gemstones.