Opal, celebrated for its captivating “play-of-color,” holds a unique position among gemstones. Designated as the primary birthstone for October, alongside pink tourmaline, it is often referred to as the “Queen of Gemstones” due to its unparalleled beauty and kaleidoscopic display of light. This article delves into the history, geological origins, gemological properties, symbolism, and care of this fascinating gem, drawing exclusively from available sources.
History and Lore
Opal’s history is interwoven with tales of beauty, superstition, and shifting perceptions. While ancient mystics believed tourmaline could inspire artistic expression, opal has long been associated with hope, purity, and love. However, a superstition arose in the 19th century, popularized by Sir Walter Scott in his novel Anne of Geierstein, suggesting that wearing an opal brought bad luck unless it was one’s birthstone. This notion, not deeply rooted in earlier history, stemmed from a plot device within the novel where an opal’s color faded with the death of its wearer.
Prior to this, opals were highly prized. The gem’s inherent instability – its tendency to change from a vibrant, glassy stone to a chalky mass of silicon dioxide – was observed, and understood to be a result of its composition as a hydrated amorphous form of silica. This understanding, however, did not diminish its allure. The gem’s ability to reflect moods, as depicted in Scott’s novel, was likely based on this observed phenomenon.
In 1952, the Jewelry Industry Council suggested pink tourmaline as an alternate birthstone for October, a change accepted by both the American Gem Society and the National Retail Jewelers Council, offering wearers a choice.
Geological Formation and Sources
Opals form in relatively low-temperature environments, typically in the cavities of volcanic rocks. They are composed of hydrated amorphous silica (SiO2·nH2O), meaning they contain water within their structure – sometimes up to 30% – which contributes to their unique properties and susceptibility to damage. The “play-of-color” is created by the diffraction of light passing through microscopic spheres of silica within the opal.
Australia is the world’s primary source of opal, producing a variety of types. White opal is found in the White Cliffs area of New South Wales, while Mintabie, Andamooka, and Coober Pedy in South Australia also yield significant quantities. Boulder opal, unique to Queensland, forms within ironstone concretions.
Ethiopia has emerged as a notable opal source, with mines near Wegel Tena in Wollo Province producing opals ranging in body color from white and yellow to orange, brown, and even black opal. Another Ethiopian mine, in Shewa Province, yields the coveted black opal.
Mexico, specifically the Querétero state, is known for its fire opal, which displays yellow, orange, and reddish-orange to red hues, sometimes with play-of-color. The mines in this region are a popular tourist destination.
Gemological Properties
Opal’s properties distinguish it from many other gemstones. It typically ranges from 5 to 6.5 on the Mohs scale of hardness, making it relatively soft and prone to scratching. This necessitates careful handling and storage to avoid damage from harder gems like diamonds, rubies, sapphires, and emeralds.
The gem is translucent or opaque, and its defining characteristic is its play-of-color – the iridescent flashes of red, orange, yellow, green, blue, and violet that appear to dance within the stone. This phenomenon is caused by the diffraction of light as it passes through microscopic silica spheres.
Opal is categorized into several types based on its body color and the presence or absence of a backing material. “Natural” opal consists entirely of precious opal. However, opals that are too thin to be cut as a natural stone are often used to create composite gems.
- Opal Doublets: These consist of a thin layer of precious opal glued to a backing of dark-colored material, such as ironstone, dark or black common opal (potch), onyx, or obsidian. The dark backing enhances the play-of-color.
- Opal Triplets: Similar to doublets, triplets add a domed cap of clear quartz or plastic on top of the opal layer. This cap protects the opal and acts as a magnifier, further emphasizing the play-of-color. Triplet opals generally have a more artificial appearance and are classified as composite gemstones rather than precious gemstones.
Lab-created opals also exist, differing significantly from resin-based imitations. Synthetic opals aim to be chemically and structurally indistinguishable from natural opals, lacking the resins or polymers found in cheaper imitations. Modern lab-created opals exhibit improved patterns, though they can still be distinguished from natural opals by their lack of inclusions and the absence of surrounding non-opal matrix.
The following table summarizes key gemological properties:
| Property | Description |
|---|---|
| Hardness (Mohs) | 5 - 6.5 |
| Chemical Formula | SiO2·nH2O (Hydrated Amorphous Silica) |
| Transparency | Translucent to Opaque |
| Play-of-Color | Present in Precious Opal |
| Specific Gravity | Typically between 1.98 and 2.20 |
| Refractive Index | 1.45 |
Symbolism and Metaphysical Beliefs
While sources primarily focus on opal’s aesthetic qualities and geological origins, it is traditionally considered a symbol of hope and purity. Astrological beliefs attribute magical properties to the gemstone, suggesting it brings happiness and love to the wearer and strengthens relationships. However, these metaphysical claims are not substantiated by gemological science.
Care and Cleaning
Due to its relatively high water content, opal is susceptible to damage from heat and sudden temperature changes. Exposure to high heat can cause cracking and scratching, potentially ruining the play-of-color. Maintaining a slightly humid environment is also recommended to prevent drying and cracking.
Cleaning opal requires gentle care. Harsh detergents or jewelry cleaners should be avoided, as they contain acids and chemicals that can damage the stone. Instead, a mixture of warm water and mild soap is recommended, used sparingly and quickly.
Special care should be taken with opal doublets and triplets, as prolonged exposure to water can weaken the adhesive binding the layers together. Opal should be stored separately from harder gemstones to prevent scratching.
Conclusion
Opal, the captivating birthstone of October, remains a gemstone of enduring allure. Its unique play-of-color, diverse geological origins, and rich history contribute to its status as the “Queen of Gemstones.” While its relative softness and sensitivity to environmental factors require careful handling, the beauty and symbolism of opal continue to captivate gemstone enthusiasts and jewelry lovers alike. Its formation in volcanic cavities, its varied sources across Australia, Ethiopia, and Mexico, and its distinctive optical properties make it a truly remarkable gem.