Alexandrite is one of the most fascinating and coveted gemstones in the world, renowned for its mesmerizing ability to change color under different lighting conditions. This magical characteristic, combined with its extreme rarity, makes it a prized treasure among collectors and connoisseurs.

The Phenomenon of Color Change

Alexandrite’s defining feature is its dramatic color shift:

• In daylight (or fluorescent light): It appears as a fresh green or bluish-green.
• Under incandescent light (like a lamp): It transforms to a reddish-purple or raspberry red.

This remarkable phenomenon is why it is often described as “emerald by day, ruby by night.” It was first discovered in the 1830s in the emerald mines near the Tokovaya River in Russia’s Ural Mountains and was named after the young Tsar Alexander II.

A Rare Geological Marvel

Alexandrite’s existence is a minor miracle of nature. It is a variety of the mineral chrysoberyl (BeAl₂O₄). Its formation requires very specific and rare geological conditions where rock types rich in beryllium (a common element in emeralds) and chromium (the coloring agent in rubies)—elements that are geologically unlikely to interact—come together. This unique combination is what creates its color-changing property and its exceptional scarcity.

Global Sources and a Legendary Stone

While Russia was the original source, today alexandrite is also found in Sri Lanka, Brazil, Madagascar, Tanzania, and India. Among these, Sri Lanka is known for producing some of the finest specimens.

A legendary example of this is the Naleem Alexandrite. At a staggering 112 carats, it is one of the largest alexandrites in the world. It was sold by the famous Sri Lankan gem merchant Naleem from Beruwala and is valued at an astonishing over $100 million, a testament to the stone’s immense rarity and value.

The Science Behind the Magic

The color change is a complex optical effect caused by how the chromium impurities within the crystal absorb and reflect light.

• Absorption Band: Alexandrite has a specific light absorption band centered at 580 nanometers, which is precisely between the absorption bands of ruby (600 nm) and emerald (550 nm).
• Human Perception: Daylight is rich in blue and green wavelengths, so our eyes, which are more sensitive to green, perceive the stone as green. Incandescent light is richer in red wavelengths, causing the stone to appear red.
• Fluorescence: Another key identifier is that alexandrite often exhibits red fluorescence under a Chelsea filter, a trait not seen in ordinary chrysoberyl, which is typically colored by iron and appears greenish-yellow.

Alexandrite Attributes at a Glance

A true alexandrite is exceptionally rare, especially in sizes over one carat with a strong color change. Its combination of beauty, mystery, and scientific intrigue secures its place as one of the most extraordinary and magical gems on Earth.