Certain gemstones exhibit a fascinating optical phenomenon where their color transforms dramatically depending on the light source. This unique characteristic makes these gems highly prized. This article explores a specific gemstone renowned for its remarkable transition from blue to purple, delving into the science behind this change and factors influencing its appearance and value.
Identifying the Color-Changing Gemstone
The gemstone known for changing color from a greenish-blue in daylight to a purplish-red under incandescent light is Alexandrite. This remarkable variety of the mineral chrysoberyl was discovered in the Ural Mountains of Russia in the 1830s. Its discovery in an emerald mine led to its mistaken identity due to its green appearance in natural light. It was named in honor of the future Tsar Alexander II.
Alexandrite’s striking color shift earned it the popular description “emerald by day, ruby by night.” Fine specimens display a distinct blue-green in natural light and a rich purplish-red or raspberry red under warm artificial light. Its rarity and distinct color change contribute to its high demand and value in the gem market.
The Science Behind the Color Shift
The color change in Alexandrite, known as the “Alexandrite effect,” arises from its unique chemical composition and interaction with light. This phenomenon is not due to pleochroism, but rather to how the stone absorbs and reflects light. Alexandrite’s color change is due to chromium impurities within its crystal lattice.
These chromium ions selectively absorb specific wavelengths of visible light. They strongly absorb light in the dark blue and yellow regions of the spectrum. Under natural daylight, the chromium ions absorb yellow and blue, allowing green and some blue wavelengths to be transmitted or reflected, resulting in a blue-green appearance.
Conversely, under incandescent light, the chromium ions absorb the limited blue and green wavelengths. Since red light is not significantly absorbed, it is predominantly transmitted and reflected, causing the gemstone to appear purplish-red. This selective absorption and varying spectral composition of light sources create the color transformation.
Factors Influencing Appearance and Value
Several factors influence Alexandrite’s observed color and its market value, with the intensity and clarity of the color change being paramount. A dramatic and distinct shift from a strong blue-green to a vibrant purplish-red significantly increases the gemstone’s desirability and price. Specimens with weak or muddy color changes are considerably less valuable.
Geographical origin also plays a significant role in value, with Alexandrite from certain regions commanding higher prices. Historically, Russian Alexandrite from the Ural Mountains was highly prized for its vivid color change, though large, high-quality stones from this source are now rare. Brazilian Alexandrite is currently highly valued, often exhibiting a bluish-green to deep purple transformation. Other sources include Sri Lanka, Tanzania, and India, each potentially offering variations in color and quality.
Distinguishing natural Alexandrite from synthetic or simulant materials is crucial for buyers. Natural stones often contain unique inclusions visible under magnification, while synthetics, though chemically similar, might lack these natural characteristics or have different types of inclusions like gas bubbles or curved striations. Lab-grown Alexandrite replicates the natural growth process and possesses the same chemical and physical properties, including the color change, but does not carry the same rarity or market value as natural stones.
Care and Considerations for Ownership
Alexandrite is a relatively durable gemstone, rating 8.5 on the Mohs hardness scale, making it suitable for everyday wear in jewelry. Despite its hardness, proper care is necessary to maintain its beauty and integrity over time. Regular cleaning can be done using a mild soap and lukewarm water solution. A soft brush, such as a soft toothbrush, can gently remove accumulated dirt and oils from the gemstone and its setting.
After cleaning, the gemstone should be thoroughly rinsed with lukewarm water to remove any soap residue and then patted dry with a soft, lint-free cloth. It is advisable to avoid harsh chemicals, abrasive cleaners, and extreme temperatures, as these can potentially damage the stone’s color or structure. While some Alexandrite can tolerate ultrasonic and steam cleaners, caution is advised, especially if the stone is set in certain metals like tungsten.
For storage, keeping Alexandrite jewelry separate from other pieces in a soft pouch or a compartment within a jewelry box helps prevent scratches. Protecting the gemstone from impacts and removing it during activities that might subject it to physical stress, such as sports or heavy cleaning, also helps preserve its condition. Applying perfumes and lotions before wearing Alexandrite jewelry is also recommended to avoid exposure to chemicals that could dull its luster.