Gemstones that display more than one color are highly desirable in jewelry for their striking visual effects. The play of color in these gemstones arises from optical phenomena that separate white light into its spectral components. One of the most famous and coveted examples is the gemstone known as alexandrite. Alexandrite has the special ability to change color depending on the type of lighting. In daylight, alexandrite appears green, but under incandescent light, it turns reddish-purple. This dual color change makes alexandrite a very rare and valuable gem.
What causes the color change in alexandrite?
Alexandrite belongs to the mineral class known as chrysoberyl. Its chemical composition includes beryllium, aluminum, and chromium. The chromium impurities in the crystal structure are what give alexandrite its distinctive colors. The specific wavelengths of light absorbed by the chromium ions make the gemstone appear greenish in daylight but purplish-red under incandescent light.
When alexandrite is exposed to natural light, the spectrum absorbed by the chromium produces a predominant green color. However, under incandescent sources rich in red wavelengths, the gem takes on a red hue. This phenomenon of appearing different colors under different light sources is called the alexandrite effect.
Where does natural alexandrite come from?
Natural alexandrite is very scarce. The premier source of alexandrite is Russia’s Ural Mountains, where it was first discovered in the 1830s. Other deposits have been found in Sri Lanka, East Africa, and Brazil, but Russian alexandrite is the most highly valued. Good quality natural alexandrite over one carat in size is considered extremely rare and can fetch very high prices at market.
Most of the alexandrite in jewelry sold today is synthetic. Developed processes allow gem labs to grow lab-created alexandrite that exhibits the same light-dependent color change. While synthetic stones do not have the cachet or value of natural alexandrite, they provide an affordable alternative for jewelry.
What are the three colors of alexandrite?
The three colors exhibited by alexandrite gemstones are:
| Green | Alexandrite appears green in daylight. |
| Red | Alexandrite appears purplish-red under incandescent light. |
| Blue | Some rare alexandrites show a greenish-blue tone in fluorescent light. |
The most distinctive and desirable color change in alexandrite is green in daylight to red under incandescent light. This dramatic shift between complementary colors is part of what makes the gemstone so appealing.
In rare specimens, a third color change can be observed under fluorescent lighting, where alexandrite may take on a greenish-blue tone. Most alexandrites will not show this third color effect, but three-color alexandrites are considered exceptionally fine.
How can you identify alexandrite?
There are a few simple tests that can help determine if a gemstone is genuine alexandrite:
- Observe color change: Place the stone under daylight, then incandescent light to look for green to red color shift.
- Check for fluorescence: Alexandrite often shows a red glow under UV light.
- Examine with a loupe: Look for inclusions typical of natural alexandrite from Russian sources.
- Conduct hardness test: Alexandrite has a hardness of 8.5 on the Mohs scale.
- Consider optical effects: Alexandrite exhibits a strong pleochroism and good refractive index.
These tests, along with an examination by a skilled gemologist, can verify whether an alexandrite is real. Natural alexandrites will have distinct chemical properties and crystal structures.
How should alexandrite be cut to maximize color effects?
Master gem-cutters orient and facet alexandrite in ways that optimize its color-change properties. The table facet should be wide to allow a large window for light to enter the stone. Shallow crown angles and open pavilion facets are also cut to maximize light passing through the gem.
Alexandrites are often cut into elongated oval, pear, or triangular shapes. These long cuts allow easier viewing of the color zoning within the gemstones. The way the crystal is oriented during cutting also impacts the visibility of the color change.
Proper orientation and faceting take skill to maximize the face-up appearance of alexandrite. Cutting should enhance the red and green hues seen at different angles as the gem or light source is moved.
How should you care for and store alexandrite jewelry?
Alexandrite rates 8.5 on the Mohs hardness scale, making it a durable gemstone for jewelry. However, care should be taken to avoid hard knocks or excessive heat.
Cleaning alexandrite requires only mild soap, water, and a soft brush. Ultrasonic and steam cleaners should not be used as they may fracture the stones. Household chemicals can also damage or erode alexandrite.
For storage, alexandrite jewelry is best kept in a fabric-lined box or wrapped in soft cloth. Pieces should be kept separate to prevent scratches from contact. Proper care will help preserve alexandrite for many years.
Conclusion
Alexandrite is a rare and fascinating gemstone that changes color based on lighting conditions. Mined mainly in Russia, natural alexandrite displays a shift from green in daylight to purplish-red under incandescent light, and occasionally a third blue-green color under fluorescent light. Alexandrite’s dramatic color change, hardness, and durability make it a prized gem. Careful cutting and orientation is required to showcase its unique properties. With proper care, precious alexandrite jewelry can be treasured as an heirloom passed down for generations.
