Opals—The October birthstone with flashes of fireworks

Forget the 4^th of July—in the world of gemstones, the opal brings fireworks to your jewelry. It’s the stone known for its “play of color,” the unique ability to flash all colors of the rainbow. Centuries ago it was believed that opals held the virtues and powers of all colored gems.

What gives opals their brilliance?

The gems are formed when water from rain seeps down into a rock’s crevasses. Once the water evaporates, the silica that’s left behind dries and hardens.

• The play of color is due to millions of microscopic spheres of different sizes, stacked in a grid pattern (the GIA compares them to “layers of ping-pong balls in a box.”)
• The spheres cause light waves to bend (refract) and they break into all the colors of the rainbow. 

Types of opals

Opals come in five different types. Here’s how the GIA describes them:

• White or light: Translucent to semi-translucent, with play-of-color against a white or light gray background color.
• Black: Translucent to opaque, with play-of-color against a black or other dark background.
• Fire: Transparent to translucent, with brown, yellow, orange, or red body color. This material—which often doesn’t show play-of-color—is also known as “Mexican opal.”
• Boulder: Translucent to opaque, with play-of-color against a light to dark background. Fragments of the surrounding rock, called matrix, become part of the finished gem.
• Crystal or water: Transparent to semitransparent, with a clear background. This type shows exceptional play-of-color.

Are opals unlucky?

No! Their bad rep started with a hit 1829 novel, “Anne of Geierstein,” in which an enchanted princess, wearing an opal, is dissolved by water. Don’t believe this—you’re lucky to have beautiful opal jewelry.

Caring for your opal jewelry

Opals, which rate from 5-6.5 on the Mohs hardness scale, aren’t very durable, especially vs other gemstones, like diamonds and sapphires. Store your opals separately, away from other pieces. And be careful of banging opal jewelry (like rings) against hard surfaces.

• The safest way to clean this October birthstone is with warm, soapy water. Other cleaning methods might damage the opal or filler material.
• Prolonged exposure to water may weaken the adhesive in opal doublets and triplets. Even natural opal can fracture if exposed to high heat or sudden temperature changes.

Buying opal jewelry

• There are three categories: Brilliant, bright, and subdued. Brilliant is the brightest and most expensive, bright is the middle, and subdued is the least bright.
• Stones may be treated by adding oil, wax or plastic. Make sure you ask the jeweler what treatments the opal may have undergone.
• Be aware of doublet or triplet stones: These aren’t solid opals; rather, they’re extremely thin slices of opal glued to a base material and covered with a thin dome of clear quartz. They’re less expensive and fine to buy, but you should know that you’re not getting a full stone.

Opals look beautiful against all skin types and add a luminous glow to any outfit. As with any gemstone, make sure your new, old, or heirloom opals have an up-to-date appraisal. I can help—contact me with questions or to set up an appointment at 617-304-0174 or by email at aimee@ambappraisal.com.

Brilliantly yours, Aimee