What was your favorite optical illusion as a child? Some of us loved mood rings and kaleidoscopes, while others favor how the ocean can change color depending on the sky. No matter what you find interesting, the complexities of human vision are just as intriguing as adults, but you need to know where to look.
One of the easiest places to find fascinating optical illusions is in gemstones. They are abundant in unique pleochroism, inclusions, and other tricks to the eye. One of the most famous visual feats in the world of fine jewelry comes from alexandrite, the color-changing gemstone.
Alexandrite is well known for its two-toned hues, switching from emerald green in the daylight to ruby red when placed under artificial light. This means that the gem has the ability to appear as two entirely different stones, with all of the shine and glamor of both.
Even more importantly, this transition has its own label: the Alexandrite Effect. It is so rare and so popular with beloved gemologists that it has been studied for over a century in depth and detail.
Allow us to explain the science behind the Alexandrite Effect and its impact on descriptions of other color-changing gemstones.
The History of Alexandrite: Where Was It Found?
Before explaining the various properties of alexandrite that contribute to its color transition, it is essential to unpack where this stone comes from. It aids in the explanation of what minerals are necessary for the gem’s brilliant hues.
Alexandrite was first discovered in the Ural Mountains of Russia in the 1830s by a team run by mineralogist Nils Gustaf Nordenskiöld. The Mountains had been famed for emerald production due to rare but incredible amounts of co-existing beryllium and chromium in their rock formations. When alexandrite was found, it was initially believed to simply be a piece of beautiful emerald (as it was only viewed in daylight).
As time transpired, the ruby redness became evident. Coincidentally, green and red were the colors of the Russian Imperial Flag, and the stone became a magnificent symbol of its rulers.
It is even named after Russian Czar Alexander II. The royal family had a hand in promoting the popularity of the gemstone throughout their reign. It spread to other nations as a symbol of Imperial Russian wealth and power.
Alexandrite has been found everywhere from Myanmar to Brazil. It is also mined in Sri Lanka and Zimbabwe, but nothing quite matches the now-defunct supplies of Russia. Brazilian gems are very clear and have a strongly saturated color change, making them the current market darling.
How Does the Alexandrite Effect Work?
Alexandrite consists of beryllium and chromium. With just the right amount of chromium impurities, the gem glints red in the right light.
We’ll explain the reason why our eyes perceive two colors shortly, but the coexistence of beryllium and chromium is less responsible for the transition than the chromium’s impurities alone (just having beryllium and chromium together creates emerald, but not ruby).
The chromium impurities are focused mainly on the yellow light wavelength, making for the perfect storm of color change. There is a 0.64-mole percent concentration of the element in stones with this effect. In those without, there is only a 0.18-mole percent concentration.
Alexandrite is also known to be blue-green and has some violet-purple reds. The color change depends on where the stone is mined from, how pure it is, and the amounts of beryllium and chromium.
How Durable Is Alexandrite?
Alexandrite is an incredibly valuable gemstone not just for its color change but also for its amazing durability. It is documented as an 8.5 on the Mohs scale of hardness, up there only with diamonds and other very sturdy fine gems.
It holds its weight against the other stones more figuratively than literally (alexandrite is rarely ever mined or available for affordable sale, over one carat). Nonetheless, it is highly wearable and versatile in jewelry pieces, beloved by many.
The gem is a part of the chrysoberyl family, known for its alluring chatoyancy effect — the “cat-eye effect.” This makes alexandrite even more special. This effect is not included in most alexandrite pieces, but it can make the stone even more valuable when present.
Other features of alexandrite include:
- Opaqueness to 100% transparency
- A total absorption that does not exceed 4700
- Three types of luminescence
- A vitreous luster
- A refractive index that ranges between 1.745 and 1.759
It is vital to keep the RI in mind because it can help determine what pieces of alexandrite are synthetic and which are genuine when it comes to picking jewelry.
Perception is Key
Beauty truly is in the eye of the beholder;
Our vision can only account for any changes in color that are a 20-degree angle or less. Otherwise, our eyes get confused and perceive the angle difference under various light sources to be a new color entirely.
The alexandrite angle change between daylight and artificial light is over 20 degrees, making it impossible for human eyes to correct what they are seeing properly and account for the transition. Therefore, we view the stone as two separate colors entirely when seen under daylight and incandescent light.
The reason why lighting matters and the gem appears differently under daylight or incandescent light sources is down to stimuli. When you look at the gem under fluorescent light as compared to artificial light, there is a different number of red stimuli and green stimuli. This causes fluctuation in our visual perception, something that we have no cognitive control over.
What Other Gemstones Look Like Alexandrite?
While the Alexandrite Effect is mostly attributed to its namesake, you can experience a similar color shift in a few other gemstones.
For example, spinel mined from Sri Lanka can transition from blue-violet under natural light to red-violet in artificial light. This is a popular dupe for alexandrite and is a common feature of fraudulent gem sales posing as alexandrite.
Pyrope garnets have the Alexandrite Effect once again because of chromium impurities. They, too, appear blue-green during the day and transition to a dark red when the sun sets.
Corundum with an element other than A13 can produce the effect as well due to chromium oxide crystals that give off red and green hues depending on the light source they are placed underneath.
Some Thai sapphires have a color transition that is at a smaller percentage compared to natural Alexandrite. This is due to a smaller amount of chromium present, once again affirming that it is the most important element at play in the significance of the stones’ color change.
Other examples of color-changing stones include Umba Valley blue sapphires and Kyanite. Izaynite has an Alexandrite Effect as well, thanks to iron and chromium levels.
If you’re looking for some color change in the United States, turn your attention to Montgomery County, North Carolina. This region is home to monazite crystals that appear light green under daylight and red-orange under artificial light. However, chromium, for the first time, is not at play here. The major component for the color change is actually neodymium.
Stunning Alexandrite Jewelry Options
If you’re curious as to what alexandrite looks like in person, we don’t blame you! Our mission at Mark Henry Jewelry is to get this precious gem in the hands of as many consumers as possible. It has largely been inaccessible to private collectors for centuries, but this is no longer the case.
Now is the best time to share it with the world and appreciate its remarkable color change and the beauty it adds to our days (and nights).
This is why we have poured so many of our resources into mining only the best quality alexandrite gems for our jewelry. Our pieces are sourced from Brazil, showcasing the highest saturation, color change percentage, and clarity on the market.
The Alexandrite Pendant
For starters to this gem, we recommend our Squarestack Alexandrite Pendant. With cable link chain options in 18kt yellow gold, rose gold, and white gold, this necklace pays attention to detail.
Five individual pieces of alexandrite, totaling 0.40 ct of the gem, evoke a floral-like shape. Petite diamonds pepper the corners of the gem and transition on the pendant above into larger stones, totaling 0.45 ct. The emphasis on alexandrite and the simplicity of the piece make it a necklace to go with any outfit or event.
The Alexandrite Ring
Our Estelle Alexandrite Ring is the perfect gift for lifelong fans of alexandrite. Yet, truly anyone can appreciate the stunning 0.50 ct center stone alexandrite and 0.36 ct pavé alexandrite featured in this piece. It dazzles with interspersed baguette and round diamonds, making for a sparkle nobody can forget.
More Than Meets the Eye
Precious gemstones are an investment. With alexandrite, you can access one stone that serves double duty and shifts to greet the light.
It is perfect to wear with day-to-night ensembles, without the pressure of purchasing two separate pieces or having to change — just think of all the fashionable possibilities.
Alexandrite Value, Price, and Jewelry Information | International Gem Society
Explanation of the Color Change in Alexandrites | Scientific Reports
Gemstones with Alexandrite Effect | GIA