Haim Medine: Inside the Perspective of a Graduate Gemologist
The natural alexandrite is recognized as an extremely rare and hard to find gemstone. Its distinguishing characteristic is the color change phenomenon, varying from a greenish blue in daylight to a reddish purple in incandescent light. The stone was discovered in the 1800's near the Ural Mountains of Russia and was considered a symbol of aristocracy, named after Tsar Alexander. Since discovery two centuries ago, alexandrite has long been coveted as one of the rarest and most cherished gemstones of all. As a result of scarce supply and limited commercial viability, the stories, impressions and symbolic desire for the stone has outstripped its actual presence in the marketplace. Today we sit down with Graduate Gemologist and Designer, Haim Medine, who has been working with alexandrite for over a decade.
Mark Henry: We always hear the words 'scarcity,' and 'rare,' when contemplating alexandrite, but what actually makes the gem so rare?
Its limited supply is probably the single most responsible factor for which the alexandrite is considered a true rarity. This is because the geographic conditions that produce alexandrite are so unusual. Today, fine specimens of alexandrite are so rare that it has essentially disappeared from the gem marketplace except as an expensive collector's gem. Combine that with the fact that experts generally agree that future discoveries are unlikely.
Mark Henry: Can you talk a little bit more about those geographic conditions? How is alexandrite formed? What minerals is it made out of?
In order for an alexandrite to be considered an alexandrite, chromium must be present in the rocks formation before the natural heat and pressure process occurs. Alexandrite is a variety of the mineral chrysoberyl that is formed through heat and pressure. Without the presence of chromium, chrysoberyl crystals can still form but they will not be classified as alexandrite and they most certainly will not have the color-changing properties that make the gem so unique and beautiful.
As with most gem formations, these processes occur deep within the Earth's crust over the course of thousands, and in some cases, even millions of years. As pressure builds deep within the Earth, magma is pushed up towards the surface penetrating several layers. These layers usually contain both stone formations with chromium and water. As the water evaporates and converts into steam, the heat from the magma reaches the water and stone formations. The steam is then trapped inside the rock formation and cannot escape and return to the Earth as water, this is when the cooling process begins in combination with the magma.
During the cooling process, minerals and elements contained in both the water and the magma combine and crystallize as water expels these impurities. When there's high traces of beryllium present in the magma, a chemical reaction occurs that causes it to combine with traces of chromium present in the rocks during crystallization. This creates a particular form of chrysoberyl known as alexandrite. This is also what determines the color and clarity of each alexandrite gem since foreign minerals present in the water, magma or surrounding rocks may also be incorporated into the final alexandrite crystal.
Mark Henry: Can you speak about the color change? What is happening to the gemstone when the color change occurs? Is it actually changing colors?
As I mentioned above in the alexandrite formation process, traces of chromium are responsible for giving the gem its ability to change color. Color change occurs within an alexandrite because the gem allows almost equal amounts of red and green light to pass through it while absorbing light most strongly in the middle of the spectrum. Hence, when you look at an alexandrite under a light that's rich in red, such as an incandescent light source, the gem looks red. Alternatively, when you look at an alexandrite under a light that's rich in blue and green, like a daylight equivalent or fluorescent light, the gem looks green. This color-change phenomenon is known as "the alexandrite effect" and it is important to keep in mind that only the hue changes, tone and saturation usually remain the same.
Mark Henry: When you are inspecting an alexandrite, what are the main characteristics you look for to determine whether it is high quality or not?
My purchasing decision is usually driven by two factors: color-change and clarity. The most important characteristic to keep in mind when I'm purchasing an alexandrite is its ability to change color. The finest stones usually have a very pronounced shift in color from bluish-green in daylight to purplish-red under incandescent light.
I also look for a medium to medium-dark tone with strong saturation.
The next factor I weigh when considering my purchase is the clarity of the gem at hand. It's extremely difficult to come across completely "eye-clean" gems although I have seen a few over the years. I do give a slight tolerance and expect to see slight internal quality characteristics within the gem I am considering. Fingerprints, included crystals, negative crystals, liquid inclusions, needles and dense clouds of needle-like inclusions, known as "silk" are all characteristics I have become familiar with seeing within the gem over the years. So long as these things do not pose any durability issues, I am okay with them if the stone has strong color-change, hue and saturation.
Mark Henry: Where are alexandrites found today and does the origin make any difference?
Alexandrites were originally found in the Ural Mountains in Russia back in 1830 and this set the standard for alexandrite quality. Today, however, the historic Russian mines yield little to no gems and stones come from other continents. Sri Lanka is a major source however their colors tend to be less desirable as they appear to be yellowish compared to the bluish-green and brownish rather than purplish-red. Brazil is another major source, and this is the source from which we get all of the stones seen in Mark Henry's designs. It is said that Brazilian stones are even more superior to the original Russian quality because of its colors. Other sources of alexandrite include India, Myanmar and Africa. When you get your alexandrite jewelry, make sure it is accompanied with certificate of authenticity and gem origin report. Alexandrite from Brazil generally tend to hold much better as a long term store of value.
Mark Henry: We understand how rare it is, but can you talk about its wearability? Should collector who own jewelry with natural alexandrite be afraid to wear on a daily basis?
It is an 8.5 out of 10 on the Mohs Scale making it a hard gem that has excellent toughness and no cleavage. This makes it an ideal gemstone for mounting in jewelry that can be worn every day. That is not to say you should be reckless and because of its value, it should be diligently cared for. To clean your alexandrite jewelry at home, use a soft brush and a solution of warm and gentle dish detergent. You can clean the gemstone thoroughly to remove any dirt or oils that can affect the gemstones brilliance.
Mark Henry: Before we finish up, can you tell us what personally fascinates you, a gemologist, about this particular gemstone?
Without a doubt it has got to be the ability to change color. I've always found it incredible that such beautiful things occur over hundreds of thousands of years by natural processes. Every gem has its own unique beauty and qualities but alexandrites stand out the most because they possess that unique ability to shift hues based on the type of light that they are exposed to. To me, that is incomparable to any other gem and that's why the alexandrite is considered by many to be the rarest of all gems.