Alexandrite is a rare variety of the mineral chrysoberyl, highly prized for its unique optical properties. It is one of the world’s most valuable gemstones, distinguished by its remarkable ability to change color depending on the light source. This characteristic contributes to its high market value.
The Unique Color Change
Alexandrite’s most captivating feature is its dramatic color-change phenomenon, often described as “emerald by day, ruby by night.” In natural daylight, it appears green to bluish-green. Under incandescent light, such as from a lamp or candle, it transforms to a purplish-red or ruby-red hue. This striking shift is known as the “alexandrite effect.”
The color change occurs due to the presence of chromium ions within the gemstone’s crystal structure. These chromium impurities absorb specific wavelengths of light, particularly in the yellow and dark blue regions of the visible spectrum. In daylight, which has a balanced spectrum, the stone reflects green and blue light, making it appear green. Incandescent light, with its richer red spectrum, causes the stone to reflect red and purplish light, resulting in its red appearance.
Extreme Rarity and Limited Supply
Alexandrite’s extreme rarity is a significant factor in its high cost, stemming from the specific geological conditions required for its formation. The gemstone forms when beryllium, a rare element, combines with chromium impurities. These two elements rarely occur together in nature, as they are typically found in contrasting rock types. For alexandrite to crystallize, beryllium-rich material must contact chromium-bearing rocks, a geological scenario that has occurred infrequently.
Historically, the Ural Mountains in Russia were the primary source, discovered in the 1830s. These deposits yielded fine-quality stones but were largely depleted within decades. While new sources have emerged since the 1980s in countries like Brazil, Sri Lanka, Tanzania, and Madagascar, high-quality material remains scarce. Limited availability, coupled with ongoing mining challenges and diminishing yields, contributes to its elevated price.
Key Quality Factors
Beyond its inherent rarity and color-change ability, specific attributes of an individual alexandrite stone influence its price. Gemologists evaluate alexandrite using criteria similar to the “4 Cs” applied to other gemstones: Carat weight, Clarity, Cut, and Color. For alexandrite, the quality of the color change itself is often considered a fifth, and most important, “C.”
A strong, vibrant color change, where the stone transitions clearly from a desirable green or bluish-green in daylight to a distinct red or purplish-red under incandescent light, commands the highest prices. Larger stones are rarer and more expensive, with prices increasing significantly for alexandrites over one carat. Clarity refers to the absence of inclusions or internal imperfections; stones with fewer visible inclusions are more valuable. A well-executed cut maximizes both the color change and the stone’s brilliance, enhancing its appeal and value.
High Demand and Collector Interest
The unique beauty and scarcity of alexandrite create sustained high demand. Its captivating color-changing property makes it highly sought after by collectors, investors, and jewelry enthusiasts. The allure of a gemstone that visibly transforms under different lighting conditions adds to its desirability.
Alexandrite also possesses historical significance. It was named after Tsar Alexander II of Russia, discovered on his birthday in 1834, and its red and green hues mirrored the colors of Imperial Russia. This historical association with royalty and prestige elevates its status. Consistent market interest, combined with limited high-quality material, pushes prices upwards, making alexandrite one of the most coveted gemstones globally.