October boasts not one, but two captivating birthstones: opal and tourmaline. While both offer stunning beauty, opal holds a unique place in history and gemology, celebrated for its iridescent play-of-color. This article delves into the fascinating world of opal, exploring its origins, geological formation, varieties, historical significance, and enduring appeal as a cherished October birthstone.
History and Lore
The story of opal stretches back millennia, with its name potentially originating from the Sanskrit word upala, meaning “precious stone,” which transitioned into the Roman opalus. Ancient Greeks believed opals bestowed the gift of prophecy and protection from disease, while Europeans once considered it a symbol of purity, hope, and truth. For centuries, opal was thought to embody the virtues of all colored stones. Even earlier, Bedouins believed opal held lightning and fell from the sky during thunderstorms.
Long before its official designation as an October birthstone by the American National Retail Jeweler’s Association in 1912, opal was highly valued. The first opals to reach the Western world came from India, and the gem’s dramatic play-of-color captivated observers for centuries. Pliny the Elder, in the first century C.E., famously described its dazzling colors in his Natural History.
Geological Formation and Sources
Opal is unique among gemstones in that it lacks a regularly ordered crystal lattice. Instead, it is a mineraloid – a substance with a similar chemical composition to a mineral but lacking a defined crystalline structure – comprised of millions of tiny silicon orbs stacked upon each other. This structure, discovered by Australian scientists in the 1960s through examination under high magnification, is responsible for its signature play-of-color. Opal is formed by the gradual natural heating of silica gel found in the cracks in rocks.
Historically, opal was mined in Ethiopia and Australia, with each location contributing to the gem’s distinctive character and hues. However, Australia became the dominant source following the discovery of rich mines there. Significant sources of fire opal, a specific variety, emerged in Mexico in the mid-nineteenth century, though availability remains limited.
Gemological Properties
Opals are categorized based on their transparency: transparent, translucent, or fully opaque. The most prized characteristic of opal is its “play-of-color,” the shifting colors in rainbow hues that appear as the stone is viewed from different angles. This phenomenon is what sets opal apart from most other gemstones.
Several distinct opal varieties are recognized, each with unique characteristics:
- Black Opal: Considered the most valuable, black opal exhibits a dark base color – ranging from black to very dark grey, brown, blue, or green – which enhances the brilliance of the play-of-color.
- White Opal: Featuring a light background color, from pure white to medium grey, white opal is more common and constitutes a large portion of the opal market. It must display some degree of play-of-color.
- Fire Opal: Originating primarily from Mexico, fire opal is characterized by its vibrant red, orange, or yellow background. Notably, fire opal is often exempt from the traditional classification of “precious” versus “potch” (common opal) as its value is derived from the intensity of its base color, and may not always exhibit play-of-color.
- Crystal Opal: Known for its transparency and superior play-of-color effects, crystal opal can display a light background hue.
- Water Opal: Similar to crystal opal, water opal may be colorless or have light base colors. It can be transparent, but the play-of-color, when present, is often more subtle.
- Boulder Opal: This unique variety combines precious opal with portions of the host rock in which it formed, creating distinctive patterns and enhancing durability.
Another type, Assembled Opal, is a human-created alternative. Opal doublets consist of a genuine opal layer attached to a backing, while opal triplets add a domed top layer of material like quartz or glass. These assembled opals offer a more affordable option while still providing a beautiful appearance.
Symbolism and Metaphysical Beliefs
Throughout history, opal has been imbued with symbolic meaning. Beyond the ancient beliefs in prophecy and protection, opal was once believed to embody the virtues and powers of all colored stones. Modern interpretations suggest that opal brings confidence and hope to the wearer. It is also the traditional stone given to celebrate the 14th wedding anniversary.
Care and Cleaning
While beautiful and captivating, opal is relatively soft. Boulder opals, due to the inclusion of host rock, are more durable. Care should be taken to protect opal from scratches and impacts. Specific cleaning recommendations are not detailed in the provided sources, but given its composition, gentle cleaning with a soft cloth and mild soapy water is generally advisable.
Conclusion
Opal, with its mesmerizing play-of-color and rich history, remains a highly prized and cherished gemstone. From its ancient origins in India to its modern-day status as a celebrated October birthstone, opal continues to captivate and inspire. Its unique geological formation, diverse varieties, and enduring symbolism ensure its place as a treasured gem for generations to come.