Alexandrite is a rare and valuable gemstone that is known for its remarkable color-changing properties. It belongs to the chrysoberyl mineral family and is named after Russian Tsar Alexander II, as it was first discovered in the Ural Mountains of Russia in the 1830s.
The defining characteristic of alexandrite is its ability to change color depending on the type of light. In natural daylight, alexandrite typically appears green or bluish-green, while under incandescent light, it shifts to a red or purplish-red hue. This optical phenomenon is called “pleochroism,” which makes alexandrite highly sought after for jewelry.
In addition to Russia, alexandrite can also be found in countries such as Sri Lanka, Brazil, and Tanzania, though high-quality alexandrite remains quite rare. Its rarity and unique properties make it one of the most expensive gemstones.
Discovery
Alexandrite was first discovered in 1830 in the Ural Mountains of Russia, specifically in an emerald mine near the Tokovaya River. The gemstone was named after the future Russian Tsar Alexander II, as the discovery coincided with his coming of age. The stone’s green and red color-changing properties aligned with the colors of Imperial Russia, further increasing its national significance at the time.
The discovery was made by the Finnish mineralogist Nils Gustaf Nordenskiöld, though at first, it was thought to be an emerald. Upon closer examination, the unique color-changing feature was identified, distinguishing it as a new variety of chrysoberyl.
Since then, alexandrite has become renowned for its rarity and optical properties, with Russian deposits producing some of the finest examples. However, significant quantities of alexandrite have also been found in Brazil, Sri Lanka, and more recently, in East Africa. Despite these newer sources, fine-quality alexandrite remains rare and highly prized.
Properties
Alexandrite has a combination of physical and optical properties that make it unique and valuable.
1. Color-Changing Ability
- Color in Daylight: Green to bluish-green.
- Color in Incandescent Light: Red to purplish-red.
- This dramatic color change is the most distinguishing characteristic of alexandrite and is due to its complex absorption of light. This optical effect is known as the “alexandrite effect” and results from pleochroism, where the gemstone displays different colors depending on the angle and type of light.
2. Hardness
- Mohs Hardness Scale: 8.5
- Alexandrite is a relatively hard and durable gemstone, making it suitable for everyday jewelry like rings and bracelets.
3. Crystal Structure
- Crystal System: Orthorhombic
- Alexandrite belongs to the chrysoberyl family, and its crystals form in the orthorhombic system. It typically forms in tabular or prismatic crystals.
4. Chemical Composition
- Chemical Formula: BeAl₂O₄ (Beryllium Aluminum Oxide)
- Alexandrite is a variety of chrysoberyl, with trace amounts of chromium (Cr³⁺) responsible for its color-changing properties.
5. Refractive Index
- Refractive Index: 1.746–1.755
- This high refractive index gives alexandrite excellent brilliance when properly cut.
6. Specific Gravity
- Density: 3.70–3.78
- Alexandrite is a relatively dense gemstone due to its chrysoberyl structure.
7. Transparency
- Alexandrite can range from transparent to translucent. High-quality alexandrite is typically very clear and free of inclusions, though some inclusions can appear in lower-quality stones.
8. Pleochroism
- Alexandrite exhibits strong pleochroism, meaning it can show different colors when viewed from different angles. This optical effect is related to the gemstone’s color-changing ability but varies with the angle of light.
9. Rarity and Value
- Due to its rarity, especially in fine quality and large sizes, alexandrite is one of the most valuable gemstones. Russian alexandrites from the Ural Mountains are particularly prized.
10. Symbolism
- Alexandrite is sometimes associated with good fortune, balance, and transformation, likely because of its ability to change color in different lighting. It is also the birthstone for June (along with pearl and moonstone).
These properties combine to make alexandrite a gemstone of rare beauty and exceptional value.
Origins
Alexandrite’s origins are rooted in its initial discovery and subsequent sources around the world. Here’s an overview of the gemstone’s key origins:
1. Russia (Ural Mountains)
- First Discovery: Alexandrite was first discovered in 1830 in the Ural Mountains of Russia. These early deposits, located in emerald mines near the Tokovaya River, are renowned for producing some of the finest and most valuable alexandrite ever found.
- Historical Significance: Named after the future Russian Tsar Alexander II, alexandrite became a symbol of Russian national pride due to its red and green colors, which matched the colors of the Imperial Russian military.
- Declining Production: Over time, the deposits in the Ural Mountains have been largely depleted, making Russian alexandrites exceptionally rare and valuable.
2. Sri Lanka (Ceylon)
- Discovery: In the late 19th and early 20th centuries, alexandrite deposits were found in Sri Lanka.
- Characteristics: Sri Lankan alexandrite is known for having slightly different color transitions compared to Russian stones, often showing shades of yellow-green or brownish-green in daylight, and purplish-red to reddish-brown under incandescent light. The stones from Sri Lanka tend to have a more muted color change, but large specimens are more common.
3. Brazil
- Discovery: Alexandrite was discovered in Brazil in the 1980s, specifically in the state of Minas Gerais.
- Characteristics: Brazilian alexandrite typically exhibits a vivid color change from greenish-blue to purplish-red. Some Brazilian stones show a more intense and dramatic color change, which is comparable to the highly prized Russian stones.
- Production: Brazil remains a major source of alexandrite today, though fine-quality stones remain rare even in this region.
4. Tanzania
- Discovery: In the 1990s, alexandrite was discovered in the Lake Manyara region of Tanzania.
- Characteristics: Tanzanian alexandrite often exhibits a strong and pronounced color change, sometimes even more intense than Brazilian or Sri Lankan varieties. It has become an important source in recent years due to its quality and availability.
5. Other Origins
- Alexandrite has also been found in a few other locations, including:
- Madagascar
- Myanmar (Burma)
- Zimbabwe
- While these sources contribute to the global supply, they produce much smaller quantities compared to the major deposits in Russia, Sri Lanka, Brazil, and Tanzania.
6. Synthetic Alexandrite
- Due to the rarity and high value of natural alexandrite, synthetic alexandrite has been produced in laboratories since the mid-20th century. It is created through a process called Czochralski pulling or flux-growth methods.
- Synthetic vs. Natural: While synthetic alexandrite can mimic the color-changing properties of natural stones, it typically lacks the same level of rarity and value, and experts can often distinguish between the two through detailed analysis.
Summary of Origins:
- Russia: Original and rarest source, prized for its intense color change.
- Sri Lanka: More common but with slightly different color transitions.
- Brazil: Produces high-quality stones with dramatic color changes.
- Tanzania: Important modern source with vivid color-changing stones.
These origins have shaped alexandrite’s rarity, value, and global market appeal.
