Why have just one ordinary, faceted gemstone when you can one extraordinary and rare gemstone that looks like two unique gems when viewed in different light? A beautiful gemstone that appears blue-green when outdoors in natural light, and purplish-red when indoors under incandescent light, for example, is a surprising and remarkable sight to behold. Also, it is extremely rare. And, because such a sensational stone is both scarce and curious, often, it is quite pricey.
However, there is good news for gem and jewelry collectors: relatively recent discoveries of gem material displaying the color-change phenomena make these special gems more attainable than ever. And, for now at least - although not cheap - many of these extraordinary gems are still quite affordable. Better still, each of the chameleon-gem varieties, pricey or not, make extraordinary, durable, heirloom-quality gemstones for jewelry.
GIA Says Phenomenal Gems Defy Description
Natural, color-change gemstones are "phenomenal gems" which display a distinct change in perceived gem body color when viewed under different types of lighting. According to the Gemological Institute of America (GIA), these rare, "phenomenal gems" display special effects that defy simple description. Color change occurs due to the unique crystal structures of a gemstone, the process of selective absorption of light rays (how a material absorbs some components of visible light and returns others), and how humans perceive color and light.
Color-change is just one of several "phenomenal" characteristics that gems may have. Other types of phenenomena include: play-of-color; adularescence; cat's-eye; chatoyancy; asterism; labradorescence; and aventurescence. All of these special-effects in gems are considered highly desirable and collectible.
Lesser-known phenomenal gems that display color-change include color-change sapphire, color-change spinel and color-change garnet. However, according to the GIA, the unusual and highly-desirable color-change effect is most well-known in a variety of the gem chrysoberyl, called alexandrite.
Alexandrite is Most Famous and Coveted Color-Change Gem
Alexandrite always shows color-change effects, according to Antoinette Matlins and A.C. Bonanno, in the book, Jewelry & Gems The Buying Guide (Gemstone Press). This simple fact distinguishes alexandrite from all other gems, which may show color-change. Alexandrite's value, the duo writes, "is based largely on the degree of change."
Rare and highly treasured alexandrite, named after Czar Alexander II, was discovered during the 1830s in the Ural mountains of Russia. For a long time, alexandrite was considered a single-source gem, which only added to its desirability and value. Today, although the sources in the Urals are said to be near-depleted, new sources of the gem are located in Sri Lanka, Zimbabwe, Brazil, Myanmar, Madagascar and Tanzania.
Color Change Alexandrite is a Most Expensive Gemstone
In Gemstones of the World, Newly Revised & Expanded Fourth Edition (Sterling), Walter Schumann explains that even though the stone is no longer considered single-source, "High-quality alexandrite is one of the most expensive of all gemstones." For many people, fine alexandrite is considered the "Holy Grail" of gemstones. After all, how often does on see a gem that completely changes hue, from one side of the color wheel to the opposite side?
According to GIA experts, the value of each finished alexandrite gem depends on the hue, tone and saturation of the two colors it shows. But equally important is the the degree and distinctness of its color change. "Fine alexandrite looks purplish red in incandescent candle or a standard light bulb. Moved to sunlight or fluorescent light, it turns green or bluish green," according to information provided in the GIA's Colored Stone Essentials class.
Saturated Colors and Dramatic Change Add Value to Alexandrite
The more pure and intense the colors, and the more distinct and dramatic the change from one color to another, the more valuable the stone (coupled, of course, with all the "regular" colored stone value parameters such as source, size, shape, cut, clarity, brilliance and finish). For example, all other characteristics being equal, a color-change alexandrite that appears brownish, grayish or with muddied colors will be worth far less than one displaying bright, purplish-red and traffic-light-green colors. Also, it is most desired that there be a crisp distinction between the two colors, and that they not be visible at the same time.
In her book, Exotic Gems, Volume 2 (International Jewelry Publications), Graduate Gemologist Renée Newman writes, "Few gems show as complete of a color change as alexandrite, and consequently the phenomenon itself is called the alexandrite effect."
In addition to its eye-appeal, alexandrite makes a fine, durable jewelry gem. The gem is quite hard, rated at 8.5 on the Mohs hardness scale.
'Alexandrite Effect' Present in Color-Change Garnet
In addition to extraordinary alexandrite, some garnet (namely pyrope-spessartine) can have superb color-change characteristics. Durable, color-change garnet is often from Tanzania and Madagascar, and the raspberry red to teal blue colors in fine garnet gems can be quite deep and intense with impressive color change.
In The Gem Trade Articles, Graduate Gemologist Richard Wise writes online that the first color-change garnet from East Africa he saw looked "exactly like an alexandrite from the Hematita strike in Brazil." He continues, "Others have compared the Madagascar color-change to Russian Uralian alexandrite as well." Moreover, Wise writes that the color change of the Madagascar garnet is "truly remarkable" and rates the stone as "extraordinarily rare." Garnet is an excellent, durable jewelry gem.
Color Change Occurs in Rare Sapphire and Spinel
Color change is present in some sapphire as well. Generally, color-change sapphire shifts from green to red, like a fine alexandrite, or from blue to purple. Green-to-red color-change sapphire (as well as the blue-to-purple), often hail from Tanzania; other changers are sourced from Madagascar, Sri Lanka, Myanmar, and East Africa. Sapphire is an exceptional jewelry stone, extremely durable, with a superb luster.
Also, according to the GIA, rare spinel may show color-change characteristics. GIA's online Featured Gemstone article titled, Spinel, reads "Some spinels show color-change, usually turning from grayish blue in daylight or fluorescent light to purple under incandescent light."
The article goes on to say that spinel, found in Sri Lanka, Tanzania, Myanmar, Thailand and Cambodia, "...is a hard, though stone that's suitable for daily wear in any type of jewelry. It will always be popular with customers who like beautiful and unusual gems." Not as well known as sapphire and garnet, spinel is nonetheless, another excellent and durable gemstone for jewelry.
Examine Gems in Different Types of Light
As a general rule, when evaluating any gem, especially a color-change stone, be sure to examine the gem in different lighting situations. A gem may appear bright and colorful in one type of light, and then go dark or muddy in the second type of light. A fine gem will display lovely color in incandescent, fluorescent and sunlight. Also, with new, energy-saving light sources on the market, and the phasing-out of traditional incandescent lights, it is wise to view a potential purchase in as many light sources as possible.
Sapphire, Garnet and Spinel Offer Excellent Value for Extraordinary Color-Change Gems
Finally, in the finest color-change specimens, most-likely, none of these alexandrite-alternative gemstones would be considered "cheap." However, fine color-change garnet, sapphire and spinel can be had for a fraction of the cost of the finest alexandrite. These unusual garnet, sapphire and spinel gemstones represent an excellent value for collectors and jewelry aficionados. Certainly, they are no less dazzling than their alexandrite counterparts. Most should be considered extremely collectible and worthy as special, heirloom jewelry gems.
Claire Eddins - Writer/editor, award-winning photographer Claire Eddins collects gems, horses, and obsesses over home, art, and design.
