10 Color Changing Gemstones That Will Simply Amaze You
Gemstones have fascinated people for millennia, but recent discoveries in the past century have revealed properties in their structure that cause fascinating optical effects. There are numerous optical effects present in different gemstones, but one of the most popular in recent years is the phenomenon called "color change."
Color-changing gemstones appear as different colors under different kinds of ambient lighting. It's also called Alexandrite Effect, due to its discovery in the gemstone alexandrite. Let's look at some of the different kinds of gemstone color changes, and what causes this stunning effect.
Gem enthusiasts sometimes refer to alexandrite by the catchphrase "Emerald by Day and Ruby by Night," in reference to its changing colors in light. Mineralogists at first believed the gem to be an emerald, until it surprised them by appearing purple-red under lamplight.
Discovered in 1830, Finnish mineralogist Nils Gustaf Nordenskiöld originally named it diaphanite (from the Greek word meaning "two appearances"), but Count Perovskii named it "Alexandrite" after Tsar Alexander II Romanov, whose military colors were green and red.
What Causes Its Color Change?
Alexandrite is the color-change variety of the mineral chrysoberyl. At an 8.5 on Moh's scale, it's one of the harder gemstones.
The change in color occurs in specimens of chrysoberyl where chromium substitutes for aluminum in the mineral's atomic structure.
Chrysoberyl's formation requires beryllium, yet beryllium and chromium rarely occur in the same types of rocks. This makes alexandrite very rare because there is only one specific situation where it can form. Because of this, there are only a few small deposits of it in the world.
Human eyes can pick up green light more easily than red light. Alexandrite appears greenish in daylight because the daytime sun provides a full spectrum of visible light. Incandescent lighting (such as from a lamp, fire, candle, coals, etc) emits less green and blue light, causing alexandrite to appear more reddish.
Some alexandrite gems also exhibit pleochroism. Gemstones that exhibit this phenomenon show different hues when observed at different angles, especially under polarized light.
Some varieties of chrysoberyl and alexandrite show pleochroism, but it's not apparent in all specimens. This effect is less distinctive than the color-change effect. Alexandrite is a trichroic stone, meaning it can show three different hues (green, red, and yellow-orange) depending on the angle you look at it.
Rarity and Value
Because alexandrite can only form in specific conditions, it's a rare and special gemstone that is prized for its color-change properties. Specimens with strong, distinct colors command the highest prices. Stones over five carats are exceedingly rare.
Sapphire comes in many different colors of varying degrees of rarity. Traditionally, the most prized sapphire color is a deep, royal blue that's richly saturated yet still transparent.
Many gemstone jewelry enthusiasts have a fair bit of knowledge of sapphires since they're one of the most prized gems amongst royalty and historical figures. People with September birthdays may also have a special fondness for it as well. Surprisingly, not many people, including those born in September, know about color-change sapphires.
In daylight (or fluorescent light), a color-change sapphire will appear a vivid blue to blue-violet. If you bring it inside under a lamp, it appears a strong purple to reddish-purple.
Some varieties of sapphire appear grey-green in sunlight and pink to reddish-violet in incandescent lighting.
What Causes Its Color Change?
Traces of metal in the sapphire cause the shift we see in its color. In the blue color-change sapphire, it's the combination of iron and titanium and chromium that give it its separate hues. Iron and titanium are responsible for the blue color in sapphires, whilst chromium is the metal that gives rubies their red color.
In the grey-green color-change sapphires, vanadium, another trace metal, is responsible for the color shift. The interaction of minerals like these with the light spectrum is how gemstones change color.
Color-change in sapphires is the same effect as that in alexandrite. Under fluorescent lighting, it's exposed to a much greater spectrum of color wavelengths. Incandescent lighting produces less blue light, allowing you to see the red hues in the sapphire that get overwhelmed in the sun.
Rarity and Value
Gem and jewelry collectors prize color-change sapphires. The most prized specimens are the ones that exhibit strong color change and have good cut and clarity.
Color-change sapphires that also exhibit bi-coloration (you can see two different color hues, no matter the lighting) can sell for even more.
Similar to sapphires, garnet comes in a vast array of colors. These colors have different mineral compositions and may contain different subtypes. One of the rarest forms of garnet is color-change garnet.
Color-change garnets exhibit one of the widest varieties of color shifts. Some change from bronze to purplish pink, others from teal to rose pink, others from grey to a pinkish purple.
The most famous color change garnet, pyrope–spessartine garnet, was discovered in the 1990s. It changes color from blue-green to purple depending on the coolness or warmth of the lighting. Similar to the grey-green color-change sapphires, this is a result of relatively high amounts of the metallic element vanadium.
Rarity and Value
Garnet itself is a popular gem for jewelry, due to its hardness, clarity, and range of colors. Many garnets are red, which causes people to confuse them with rubies.
Color-change garnet is the rarest form of garnet. Its value depends on its color and other qualities; there are many variables that can play a factor. Blue to purple color-change garnets are particularly rare. In 2003, a 4.2-ct blue color-change garnet sold for $6.8 million.
Another rare and valuable type of garnet is Tsavorite, which only recently became popular in jewelry (1976, 16 years after its discovery). It's is known for its unique vivid green appearance.
In the 1970s, miners discovered large, transparent, gem-quality diaspore crystals in Turkey. They noticed that it appeared as different colors under different lighting. Diaspore comes from the Greek word "diaspora" which means "to scatter," which describes the color effect in this mineral.
Diaspore was originally discovered in 1801 in Russia and remained under the radar outside of mineralogy. The more recent discovery of the Turkish mine led to its popularity in the jewelry market. One individual privately owns this mine.
You can identify diaspore gemstones from this mine by their trade names, "Zultanite" and "Csarite." Only diaspore specimens from this one location can be sold under these trademarked names. Specimens from other locations still go by its mineral name, "diaspore."
Diaspore is naturally found as a yellow, green, or brown earthy color. It changes from a brownish green in sunlight to a champagne color in incandescent lighting. This color change is more noticeable in larger gems (over five carats).
Its hardness ranges from 6.5–7 on Mohs scale, making it pretty durable. It also has perfect cleavage, which means that it can split more easily than other gemstones, so you have to be more careful if you wear it as jewelry. Look for diaspore that is cut properly and graded to reduce the risk of splitting.
Diaspore can exhibit chatoyancy, or cat's eye effect. This reflective effect appears as a single band of light across the surface of the gemstone. Like alexandrite, it can also exhibit pleochroism.
Rarity and Value
Diaspore not an uncommon mineral, and you can find it all over the world. Gem-quality diaspore that's high in carats is rare, however, as it is only found in abundance in the one mine in the Anatolian Mountains in Turkey.
High-carat Zultanite is valuable and in-demand. The larger stones display exceptional color play.
It's important to look out for fakes since some vendors sell different minerals under this name. Synthetic diaspore displays neon colors rather than earthy tones. Alexite is the trade name for a synthetic glass version sold in India.
Real Zultanite will come with a certificate of authenticity. Synthetic Zultanite is often very colorful but doesn't display a true Alexandrite Effect. It's hard to synthesize the natural effect of gemstones that change color.
Fluorite is known for its beautiful optical effects. It's one of the most fluorescent gemstones although it isn't popular in jewelry due to its softness (4). It glows bright blue-violet under UV light.
Its fluorescence is so strong that it's one of the few gems that exhibit fluorescence in natural sunlight. Rubies are one of the few other gems with this effect.
It wasn't until recently that color-change fluorite appeared on the market. It's more popular with mineral collectors than jewelry fanatics.
The prices and values of fluorite vary quite a bit. It depends on the size and quality of the stone, as well as its other optical qualities.
Other Optical Color Effects
These first five gemstones all make up the category of Alexandrite Effect color-change. There are other minerals that produce this effect, including andesine and spinels.
Other gemstones have equally intriguing optical effects, but due to different phenomena. Let's look at some other gemstones with forms of color play.
Tourmaline is a popular gem in jewelry due to its relative hardness (7–7.5) and its color effects. Like alexandrite, it can exhibit color change. It can also produce a cat's eye effect.
In addition to these two effects, a geologist recently discovered that a Tourmaline from Tanzania displayed another remarkable color effect. This phenomenon, called the Usambara Effect, causes the tourmaline to shift from green to red dramatically when it reaches a certain thickness.
You can see both the green and red color at once in tourmaline gems that have this effect.
Large tourmaline or rare colored tourmaline (such as emerald green chrome, raspberry red and neon blue) can demand high prices. Color-change tourmalines are especially prized.
An opal's unique formation causes it to contain water within its structure. This gives it a rainbow of iridescent colors. This effect is called opalescence, or adularescence.
Opals also display another optical effect. If you examine a precious opal (gemstone quality), you'll notice that the colors seem to flicker in the light. This is called the Schiller Effect.
Opals can be extremely valuable. Their price is determined by the variety of opal and its colors. Black opal is the most valuable type of opal and can cost over $10,000 per carat.
Labradorite is the most popular form of feldspar as a faceted gem. Inclusions of minerals such as hematite and copper create a wide range of different gemstone color varieties. Labradorite is becoming more and more popular due to its special effect called labradorescence.
This effect causes the labradorite to display dark, metallic-like shimmering, usually in shades of blue and green. Labradorite from Oregon can also have pleochroism.
Labradorite isn't the most prized gemstone, but certain colors can be highly collectible and rare. Natural red, green, and watermelon (both green and red) specimens from Oregon are the most valuable. Red and green sunstone labradorite is the most desirable.
The reason why the cut of diamonds is so important is that an optimal cut can produce a fire effect. The dispersion of light produces a vast array of shining colors. This effect is similar to the rainbows produced by a prism.
Only diamond and zircon have strong enough refractive properties to produce a distinct fire effect.
Diamonds with excellent cut and clarity produce a fire effect, and these qualities are key determiner's in a diamond's value.
Moonstone is another member of the feldspar group. During formation, the minerals orthoclase and albite separate into alternating layers. When sunlight falls between these tiny layers, it produces a scattering of colors.
The Romans admired moonstone, as they believed it consisted of solidified rays from the moon. This gemstone was also prized in jewelry during the Art Nouveau movement.
The most valuable moonstone is colorless and transparent. These gems came from Myanmar, but their popularity left the mine empty. To get your hands on one of these, you have to get them from another collector, which escalates the price.
Earth's Hidden Rainbow
It's mind-blowing to think of how many different dazzling gemstones could be hiding under the earth or tucked away in mines. Fortunately, there are plenty of gemstones available to choose from if you want to wear jewelry that's extra special.
It's no wonder why colored gemstones for engagement rings are becoming more popular than diamonds in recent years. There's nothing like a color-change gemstone to start a conversation; most people don't even know about them. If you're a gem aficionado and want to discover more colored gemstones, check out our rings.