Six Displays of Optical Phenomena in Gemstones

By Robin Skibicki

There are several varieties of gemstones that display optical phenomena, which describes the many ways light interacts with the structural features or inclusions (internal characteristics) in the gemstone. Often these gemstones will be fashioned in a particular way that best displays these effects.

The science of optical phenomena can be fascinating, although the mystery and allure of these effects are what initially attract us! In this article, we’ll discuss six of the most familiar (and magical) displays of optical phenomena in gemstones.

Adularescence

Adularescence is the phenomena typically seen in moonstone, which is a member of the feldspar family. It produces a billowy soft blue to milky white light that appears to move across the gemstone. This occurs when light hits the alternating layers of albite and orthoclase, which are two differing forms of feldspar within the gem.

The layers of feldspar interfere with the light rays causing them to scatter and the eye to observe adularescence. The effect is best seen when the gemstone is cut en cabochon [en CAB-ah-shawn]—that is, with a polished, domed top and a flat or slightly rounded base.

 

Asterism

Asterism, or stars, relates to the four- or six-rayed star pattern of light produced by the fibrous inclusions, elongated needles, or growth tubes in a gemstone. This singular, celestial-like phenomenon is best seen in a gemstone cut en cabochon.

 

Chatoyancy

Chatoyancy [sha-TOY-an-cee] is also known as “cat’s eye.” Fine needle-like or fibrous inclusions within the gemstone are what causes this effect. Again, stones fashioned as cabochons display this effect the best.

 

Color Change

A small number of gemstones display the color change optical phenomena. Depending on the lighting environment, the color change appearance can vary due to the shifting wavelengths. The technical term for this is photochromism or photochroism; “color-change” is a lot easier to say!

The best-known color changing gemstone is alexandrite. When viewed in sunlight, it appears greenish. When placed under incandescent light, it appears reddish. Other varieties of color-changing gemstones include sapphire, garnet, spinel, diaspore, and tourmaline.

 

Labradorescence

Labradorscence [lab-ra-dor-es-cence] is an optical characteristic often seen in labradorite. The effect is a spectacular play-of-color that is metallic or iridescent, displaying blue, green, red, orange, and yellow. This is an interference effect within the gemstone caused by internal structures that selectively reflect only certain colors.

 

Play-of-Color

Play-of-color is created by a combination of diffraction and interference and is the result of the microstructure of opal: the chameleon of a thousand colors!

Opals are made up of many layers of small, stacked spheres of silica. These spheres diffract light, splitting it into a spectrum of colors. The layers of these spheres create interference allowing certain colors to dominate, depending on the angle the opal is viewed.

 

Are you ready to see some of these displays in person? Visit a credentialed AGS jeweler near you and ask to see some gemstones that exhibit optical phenomena!

The AGS Suppliers’ Reception and Showcase

Each year during the American Gem Society’s (AGS) annual conference, Conclave, we feature an exclusive event called the AGS Suppliers’ Reception and Showcase. This special evening gives our supplier members the opportunity to showcase their incredible jewelry to their fellow AGS members, the AGS retailers.

What makes this event so special is when we do a showcase…we do it up right! This year, with the generous sponsorship of the bridal magazine, The Knot, our showcase featured 23 AGS members whose most gorgeous and luxurious jewelry was worn by models in wedding gowns.

This showcase is not open to the public, but we’d like to give you a special peek into the fashions and festivities that took place this year!

This showcase is not open to the public, but we’d like to give you a special peek into the fashions and festivities that took place this year!

Stay tuned for more images featuring our AGS members.

Visit an AGS-certified jeweler near you and ask them to show you some of their favorite designs. And if you have a special design in mind, do not hesitate to ask—they’ll be happy to find it for you or bring your idea to life!

October’s Birthstones are Bursting with Color

octoberbirthstonesOctober features two incredible birthstones: opal and tourmaline. They each display an exciting and intense array of colors, making them popular choices for jewelry designers and collectors.

Opal

The name “opal” derives from the Greek Opallos, meaning “to see a change (of color).” They range in color from milky white to black with flashes of yellow, orange, green, red, and blue. An opal’s beauty is the product of contrast between its color play and its background.

Opal is a formation of non-crystalline silica gel that seeped into crevices in the sedimentary strata. Through time and nature’s heating and molding processes, the gel hardened into the form of opals. The opal is composed of particles closely packed in spherical arrangements. When packed together in a regular pattern, a three-dimensional array of spaces is created that gives opal its radiance.

Approximately 90 percent of the world’s precious opal comes from Australia. The following are other countries that produce precious or fancy varieties: Brazil, Mexico, United States, Hungary, Peru, Indonesia, Honduras, Guatemala, Nicaragua, Slovakia, Czech Republic, and Ethiopia.

Like fingerprints, each opal is totally unique! To get a really good look at the opals in these designs, click on the images below for a larger view.

Lightning Ridge Collection

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Blue-green black opal accented by fine white princess cut diamonds and round brilliant cut diamonds.

 

Lika Behar Collection

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Sterling silver and 24k gold “Ocean” necklace, featuring a one-of-a-kind boulder opal framed by diamonds.

 

Parlé

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Australian black opal and diamond earrings set in 18k yellow gold.

 

Yael Designs

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An 18k rose gold bracelet featuring rose cut fire opals and brilliant cut white round diamonds.

 

Tourmaline

Since tourmaline is available in a wide variety of colors, it is ideally suited to almost anyone’s taste. It is known for displaying several colors in the same gemstone. These bi-color or tri-color gems are formed in many combinations; the gemstones with clear color distinctions are highly prized.

One multi-color variety is known as watermelon tourmaline and features green, pink, and white colors bands. To resemble its namesake, the gemstone is cut into thin slices having a pink center, white ring, and green edge.

Tourmaline is found in many localities including Brazil, Afghanistan, East Africa, and the USA.

The following designs feature the varying hues of tourmaline. Click on the images to see a larger view.

 

Erica Courtney

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“Rain Drop” 18k yellow gold studs featuring
Paraíba tourmaline accented with diamonds.

 

Supreme Jewelry

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This unique ring displays a butterfly fluttering around petals of  sliced tourmaline, framed by diamonds.

 

Omi Privé

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A cushion cut pink tourmaline and diamonds are set in platinum and 18k rose gold.

 

Crevoshay

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“California Dreaming” is an 18k gold pendant artfully displaying the many colors and varieties of tourmaline.

On behalf of everyone at AGS, we send our best wishes to those celebrating a birthday or anniversary in the month of October!

If you are shopping for opal or tourmaline jewelry, search for an AGS credentialed jeweler near you: www.americangemsociety.org/en/find-a-jeweler.