October Birthstones

Opal’s kaleidoscopic play-of-color can suit many changing moods and tastes, making this gemstone appropriate for anyone. It is also the traditional gift to celebrate 14th wedding anniversaries. 

Like diamonds, opals can be evaluated by color, clarity, cut, and carat weight. But these unique gemstones also have several additional conditions to consider.

Opal gems and jewelry should be stored in a place where they aren’t exposed to high temperatures or low humidity in order to avoid dehydration and crazing. Be sure they are in a padded cloth bag to avoid being scratched by other jewelry. For longer storage periods, place your opal in cotton wool with a few drops of water.

Color
Color is the key factor of opal quality: both the background “body color” and the flashing “play-of-color.” Dark backgrounds provide more contrast against vivid play-of-color, making black opal more highly valued than milky white varieties.

Warm colors like red and orange are generally rarer and more valuable than common blues and greens, although color range and coverage also play a role.

Pattern
Pattern is another factor unique to opal. Descriptive names like “stained glass,” “peacock,” “rolling fire,” and “Chinese writing” distinguish opal patterns. Gemologists typically prefer large, concentrated patches over small specks.

Clarity
Different opal varieties have varying clarity standards. Crystal opals should be transparent, while opacity makes black opals more valuable. A cloudy, milky haze lowers any opal’s value, and may indicate instability.

Due to high water content, opal can easily crack or “craze” under extreme temperatures, dehydration, or direct light. Crazed opal sells at much lower prices, and is more susceptible to fracture. Even high-quality opal demands delicate care to preserve its unique beauty.

Cut
Fine opals are often cut into irregular shapes to emphasize play-of-color. When possible, opals should be cut cabochon with rounded domes. But most opal comes in thin layers, which are commonly mounted on another dark stone like onyx or obsidian (as a doublet) and sometimes capped with clear glass or plastic (as a triplet) to make this fragile gemstone more wearable.

Opal gems and jewelry should be stored in a place where they aren’t exposed to high temperatures or low humidity in order to avoid dehydration and crazing. Place them in a padded cloth bag to avoid being scratched by other jewelry. For longer storage periods, place your opal in cotton wool with a few drops of water.

Opal gemstones may be treated with wax, oil, smoke, plastic, or other additives to enhance luster. Identifying enhancements or synthetic materials may require specialized lab equipment, so it’s best to work with an American Gem Society jeweler who understands the criteria that determine opal’s value.

Find a jeweler near you to help pick out the right opal for your preferences.