Alexandrite is one of the most fascinating and rare gemstones in the world, known primarily for its unique color-changing ability. Often referred to as an “emerald by day, ruby by night,” Alexandrite is a member of the chrysoberyl mineral family, prized for its rarity, beauty, and optical phenomena.
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Discovery of Alexandrite
Alexandrite was first discovered in the Ural Mountains of Russia in the early 19th century, during a period when Russia was emerging as a major producer of gemstones. The story of its discovery is often tied to the mineralogist Nils Gustaf Nordenskiöld, a Finnish scientist working in the area. While Nordenskiöld is credited with identifying the stone, its discovery date is disputed. Some reports say it was discovered in 1830, while others suggest 1834.
The gem was found near the Tokovaya River in the Ural Mountains, a region rich in mineral deposits, including emeralds. Initially mistaken for emerald, Alexandrite quickly gained attention for its striking ability to change color in different lighting conditions. By the light of day, it exhibited a green to bluish-green hue, but under candlelight or incandescent light, it appeared red or purplish-red.
The stone was named in honor of Tsar Alexander II of Russia, as it was said to have been discovered on the future tsar’s birthday. Alexandrite’s red and green colors also mirrored the national military colors of Imperial Russia, making it an especially patriotic symbol during that era.
Properties of Alexandrite
Alexandrite is prized for its rarity, beauty, and its unusual optical properties. Below are the key properties that define this gemstone:
1. Color Change
The most remarkable and defining property of Alexandrite is its ability to change color depending on the type of light it is exposed to. This phenomenon is known as pleochroism. In daylight or fluorescent light, Alexandrite typically appears green, bluish-green, or sometimes even yellow-green. However, under incandescent light, such as candlelight or a tungsten bulb, it shifts dramatically to red, purplish-red, or raspberry hues.
This color change is caused by the gem’s unique way of absorbing light, specifically due to the presence of trace amounts of chromium in its structure. The level of chromium, along with how the stone has crystallized, affects the intensity of the color change.
2. Chemical Composition
Alexandrite belongs to the chrysoberyl family, whose primary chemical composition is BeAl₂O₄ (beryllium aluminum oxide). What distinguishes Alexandrite from other types of chrysoberyl is the presence of chromium (Cr³⁺) ions, which are responsible for its color-changing property.
3. Hardness and Durability
On the Mohs hardness scale, Alexandrite measures 8.5, making it a relatively hard and durable gemstone. It is surpassed only by diamonds, sapphires, and rubies, which means Alexandrite is suitable for various types of jewelry, including rings, earrings, and necklaces. Its toughness, combined with its resistance to scratching and breaking, makes it a prized gemstone for fine jewelry.
4. Refractive Index and Luster
The refractive index of Alexandrite ranges between 1.746 and 1.755, giving it a high brilliance and sparkle when cut properly. Its luster is described as vitreous, meaning it has a glass-like sheen that enhances its aesthetic appeal.
5. Transparency
Most Alexandrite stones are transparent to translucent, and the highest quality stones exhibit perfect transparency with no visible inclusions. However, due to its rarity, some stones with slight inclusions are still highly valued if they show a strong color change.
6. Crystal Structure
Alexandrite crystallizes in the orthorhombic system, which means its crystal structure is based on three mutually perpendicular axes of unequal lengths. This structure contributes to its pleochroic properties, allowing the stone to display different colors from different angles.
Origins of Alexandrite
The original and most famous source of Alexandrite is the Ural Mountains in Russia, but over time, additional deposits have been found in various parts of the world. However, none of these sources have produced stones with the same quality, intensity of color change, or historical significance as the Russian gems.
1. Russia
The Ural Mountains remain the most legendary and significant source of Alexandrite. The stones found in Russia during the 19th century are renowned for their vivid color change, shifting from a deep green to a rich red. Russian Alexandrite from this period is exceedingly rare today and highly sought after by collectors. The mines in the Ural Mountains were largely depleted by the late 19th and early 20th centuries.
2. Sri Lanka
After the depletion of the Russian mines, Sri Lanka (Ceylon) became an important source of Alexandrite. The stones found here are generally lighter in color than their Russian counterparts, often appearing in shades of greenish-yellow or olive green in daylight and brownish-red or purplish-red under incandescent light. Despite these differences, Sri Lankan Alexandrite still exhibits the characteristic color change and is valued in the gem market.
3. Brazil
In the 1980s, significant deposits of Alexandrite were discovered in the state of Minas Gerais, Brazil. Brazilian Alexandrite tends to have a bluish-green color in daylight and a purplish-red hue under artificial light. Some Brazilian stones show a remarkable color change, comparable to Russian Alexandrite, making them a valuable alternative.
4. Other Locations
In addition to Russia, Sri Lanka, and Brazil, smaller deposits of Alexandrite have been found in India, Tanzania, Madagascar, and Myanmar. However, these stones are generally considered of lower quality due to less pronounced color changes and the presence of more inclusions.
Modern Applications and Value
Alexandrite is one of the birthstones for the month of June, sharing this designation with pearls and moonstones. It has become a symbol of luck, prosperity, and intellect in modern gemology, often linked to the wearer’s ability to adapt to change due to its color-changing properties.
Because of its rarity, Alexandrite is extremely valuable. High-quality Alexandrite, especially stones over one carat that exhibit a sharp and vivid color change, can fetch tens of thousands of dollars per carat. The Russian variety, in particular, commands a premium due to its historical significance and the depletion of its original mines. However, Alexandrite from Brazil or Sri Lanka can still be a more affordable option for those seeking this rare gem.
Synthetics and Imitations
Due to the rarity and high value of natural Alexandrite, synthetic versions have been produced in laboratories since the 1960s. These lab-created stones are made using the Czochralski or flux growth methods and have the same chemical and physical properties as natural Alexandrite. They exhibit the same color-changing ability and can be visually indistinguishable from their natural counterparts.
There are also imitations of Alexandrite, often made from color-change corundum or color-change garnet, which can mimic the stone’s color change but lack its other physical properties. These imitations are more affordable but do not carry the same value or rarity as true Alexandrite.
Conclusion
Alexandrite is a gemstone that continues to captivate gem enthusiasts, collectors, and jewelers alike. Its unique ability to change color under different lighting conditions, combined with its historical significance and rarity, makes it one of the most sought-after gems in the world. Whether it’s a stunning piece of Russian Alexandrite or a fine Brazilian stone, owning an Alexandrite is like possessing a piece of geological history that sparkles with both beauty and mystery.
