Why settle for one color when you can have ALL the colors?
Gemstones that display unique colors or optical effects have always held a special fascination for collectors and consumers. Called “phenomenal gems” by gemologists, they all feature an exceptional optical effect that sets them apart from their more traditional counterparts. Sapphire, spinel, garnet, tourmaline and Turkish diaspore gems all feature varying degrees of optical or color-based phenomena, but the more famous (and valuable) include star rubies and sapphires and the chrysoberyl alexandrite and cat’s eye gems.
This unique gem – discovered in Russia’s Ural Mountains in 1830 – was named for Czar Alexander II. It’s the rarest form of chrysoberyl gemstone, highly prized for its ability to exhibit a distinctive color change when viewed under sunlight or incandescent light sources. This phenomenon, often called the “alexandrite effect,” makes it one of the most valuable of all color change gems. While good quality alexandrite has few inclusions, gems with rare, needle-like inclusions show both color change and a cat’s-eye: two phenomena in one gem.
Strict standards of color change must be met and observed before a chrysoberyl is graded as alexandrite. Color ranges are graded according to which color is dominant. For example, those beginning with a higher case letter, such as Red purple, indicates red as being the dominant color, while purple is secondary. Here are examples of color ranges found in genuine alexandrite gemstones:
- blue Green
- Very pale blue Green
- Pale Green
- yellow Green
- orange Red
- Slightly purple Red
- Purple Red
- Red purple or Purple red
You shouldn’t have to guess about these color changes, nor should the color change be feeble; it should be dramatic and unquestionable. Any of the color combinations listed above can and should be identified as alexandrite and graded as such. All other color combinations, especially those with a brownish color cast, are merely “color change chrysoberyl”.
Today, there is almost no production of Russian alexandrite and almost all of the original Russian gems are in museums or private collections. This is no surprise, because stones from the original mines commonly command $10,000 to $40,000 per carat. However, fine stones are found in Sri Lanka, Brazil, Myanmar, Tanzania, Madagascar, Zimbabwe and India.
Color change garnet is an especially rare and valuable gemstone. Like alexandrite, it’s highly valued for its distinct ability to change color depending on the type of light source under which it’s viewed. Although the color change phenomenon is often mistaken for pleochroism – the ability to exhibit different colors depending on the viewing angle – this is not the case in high-grade garnets.
There many color change combinations possible, so specimens should be observed under a variety of lighting conditions, including early morning and late afternoon daylight, fluorescent light, incandescent light and candlelight. The most common shift is from red to green, although in daylight, colors vary from green to gray and rarely, blue. Under direct incandescent light, colors can appear violet to purple. Under candlelight, a garnet can exhibit a deep, almost blood-like color. Other combinations include reddish-orange to red, greenish-yellow to pink-red, light red to purplish-red and bluish-green to light violet-purple.
Today, the leading supplier of color change garnet is East Africa, particularly the Umba Valley in Tanzania. Other sources include Sri Lanka, Madagascar, Norway and the United States.
In addition to being the national gemstone of the United States, tourmaline is the most colorful of all gemstones. According to an ancient Egyptian legend, it passed through a rainbow on its journey to Earth, bringing all of the colors with it.
Despite its amazing range in colors, not all tourmaline gems have the same value. Some varieties are especially rare and desirable, while others are almost as inexpensive as quartz. The rarest and most expensive type of tourmaline is the Paraiba tourmaline, a glowing, electric blue-green variety first discovered in the Brazilian state of Paraiba in 1989. Analysis showed that this unique phenomenon was due to the presence of copper and manganese.
Tourmaline gems often feature two or more colors, change color when viewed under various lighting situations or display the cat’s eye phenomenon. No two tourmalines are exactly alike. While there are numerous deposits around the world, high-quality stones featuring bi- or multi-colored stones are rarely found. For this reason, the price spectrum is almost as broad as that of its unbelievable color range.
This gem’s name comes from the Greek word diaspora, meaning, “to scatter”. Another rare gem first discovered in the Ural Mountains of Russia (1801), it’s found in numerous locations around the globe. Some of the finest examples of diaspore are from Turkey’s Anatolian Mountains.
One of the lesser-known color change gemstones, diaspore is both prized and criticized for its properties. Because most diaspora gems are colorless to very pale, the beauty shines when there is enough color saturation to display the color change phenomenon.
Daylight and most fluorescent lighting will show green hues, while candlelight and incandescent light brings out pink tones. Unlike color change garnets, diaspore does possess the property of pleochroism. It’s imperative that each stone’s cut doesn’t mask or compete with the stone’s color change capabilities.
On the minus side, while diaspore does resist scratching, it is brittle and splits if hit with sufficient force in the right spot. The value of each gem depends on color saturation, the degree of color change and the lack of modifying colors, such as brown. Clean stones are rare, so minor inclusions are common. Cats eye varieties show prominent inclusions, but this is also to be expected.
Because color-change gems are so rare, prices tend to be higher than for non-color-change specimens of the same variety. Whether you’re a collector or just want to own a unique and beautiful rarity of nature, color-change stones make wonderful jewelry.