So, did you guess right? It turns out that these two stones are in fact one and the same gemstone: Alexandrite!
|Alexandrite, Chrysoberyl. Photo Courtesy of www.dorondiamonds.com|
Is this witchcraft, you ask? Sorry to disappoint you, but there's no funny business going on here; Alexandrite's most coveted and desired property is the color-change effect! As the name suggests, this property is the ability for certain gemstones to display different body colors when viewed in certain light sources.
In order to properly explain how this works, we must first explain a few things about light and color.
|The electromagnetic spectrum (top); a close up of the visible light spectrum (bottom). Photo courtesy www.artinaid.com|
For the purpose of this entry, we will go on the generally accepted assumption that energy travels in wavelengths. The higher the frequency, the greater the amount of energy that is being transmitted. This is how we can begin to understand the differences between energies such as the x-rays we use at the dentist to the micro-waves in our microwave. One can penetrate bone, while the other can heat up your dinner. Light is also an energy; the energy that can be seen by the human eye is called the visible light spectrum and spans a range between approximately 400-700 nm. In this range, we can see all of the colors of the rainbow classified in their respective wavelengths. The various types of lighting that are available to us will be dependent on the wavelengths that are being utilized. In other words, incandescent light (which traditionally has warmer tones) will emit light energy from different wavelengths than fluorescent light or even daylight (which will have colder tones).
|A rough crystal of Alexandrite, Chrysoberyl. Photo courtesy of www.gia.edu|
In certain gemstones, including Alexandrite, the chemical composition and structure of the gem are such that a simple change in the light source will impact the way that the stone will absorb the energy; in turn it can drastically change the body color of the stone. Alexandrite of the finest quality, can range from a pleasing blueish green in daylight to raspberry red in incandescent light. Of course, the locality of the deposit will effect the colors variously, but the lasting point is that the change is quite dramatic.
|Alexandrite with the cat's eye effect, viewed in different lighting. Photo courtesy of www.gemologyonline.com|
Apart from its ability to change color, Alexandrite can also display chatoyancy or a cat's eye effect, (something we'll cover in a later post). As a member of the Chrysoberyl family, Alexandrite is a rather hard stone (8 on the Mohs scale) and has quite a high lustre; making it an interesting choice. Not to mention it's one of June's birthstones! It also happens to be one of Bergamot Gems' co-owners' favorite stones :)
Just in case you're curious, other stones can also display the color change effect. Examples include: synthetic color-change Sapphire, synthetic Spinel and even certain Garnet.