Opal, the captivating birthstone of October, is a gemstone celebrated for its unique “play-of-color”—a mesmerizing display of iridescent hues. While traditionally recognized as the sole October birthstone, it now shares this honor with tourmaline. Revered throughout history for its beauty and believed to bring luck and hope to its wearer, opal presents a fascinating study in geological formation, cultural significance, and gemological properties. This article will delve into the history, origins, varieties, and symbolism of this remarkable gemstone, drawing solely from available sources.
History and Lore
The origins of the name “opal” are somewhat debated, with most tracing it back to the Latin opalus. Some believe the term derives from the Ancient Greek opallios, meaning “to see a change in color,” aptly describing the gem’s defining characteristic. Others suggest a Sanskrit origin, upala, meaning “precious stone.” Regardless of its etymological roots, opal has been prized for millennia. In antiquity, it was considered a rare and valuable gem, favored by European royalty. Historically, the primary source of opal was Červenica, located beyond the Roman frontier in present-day Slovakia.
The gem’s association with luck dates back centuries, and it was long believed to bring good fortune to those who wore it. While its listing as a birthstone by the American National Retail Jeweler’s Association occurred in 1912, its historical significance predates this designation by thousands of years. Today, it is considered a stone of hope, achievement, and self-expression.
Geological Formation and Sources
Opal’s formation is a unique geological process. It arises from a combination of silica and water that flows into cracks and spaces within the earth. Over time, this silica-rich solution gradually hardens and solidifies, resulting in the formation of opal.
Australia currently dominates the global opal supply, accounting for over 95% of the world’s production. Several unique varieties originate from this country, including white opal found in Coober Pedy and White Cliffs, and boulder opal, characterized by its reddish hue due to the presence of ironstone, found in Queensland. Lightning Ridge is particularly renowned for its black opal, a highly prized variety.
However, Australia is not the sole source. Significant deposits are also found in Ethiopia, Brazil, and the United States, with notable occurrences in Peru, Mexico (specifically the state of Querétaro), Oregon, Idaho, and Nevada. Peruvian opal, often referred to as blue opal, is a semi-opaque to opaque blue-green stone. Mexican fire opal, typically translucent with a yellow to red base color, is another notable variety.
Gemological Properties
Opal is classified as a mineraloid, rather than a true mineral, due to its amorphous structure – lacking a defined crystalline lattice. Its defining characteristic is the “play-of-color,” a phenomenon caused by the diffraction of light through microscopic silica spheres within the stone. This creates the vibrant flashes of color that make opal so desirable.
Several varieties of opal exist, categorized by their body color and the presence or absence of play-of-color. These include:
- Precious Opal: Exhibits play-of-color. Colors range from clear, white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Red against black is considered the rarest and most valuable.
- Common Opal: Lacks play-of-color.
- Blue Opal: Can be either precious or common, displaying blue body tones ranging from bluish-black to sky blue. Precious blue opal may exhibit flashes of green, blue, and purple.
- Orange Opal: Often referred to as fire opal, it can be translucent or transparent with orange body color, sometimes accented with red and yellow. Precious orange opal displays a range of play-of-color.
- Yellow Opal: Also part of the fire opal family, exhibiting shades from pale canary yellow to dark mustard. Precious yellow opal can show green, blue, red, and orange play-of-color.
- Black Opal: Characterized by a dark background (black to dark blue or gray) that accentuates the play-of-color.
- Boulder Opal: Contains ironstone, giving it a reddish hue.
- Triplet Opal: A composite stone consisting of three layers: a backing material, a slice of natural opal, and a domed cap of clear quartz or plastic. This is one of the more affordable types of opal.
- Doublet Opal: Another composite stone, combining a layer of precious opal with a strong backing or black material to simulate black opal. Doublet opals are thinner than natural opals and more expensive than triplet opals.
- Peruvian Opal: A semi-opaque to opaque blue-green stone that does not exhibit play-of-color.
Diatom opal is a less common form, created by the skeletal remains of diatoms (a type of algae). These microscopic structures, composed of hydrated silicon dioxide, exhibit structural coloration and appear as tiny opals under a microscope. Diatomite, the sedimentary rock formed from diatom remains, has industrial applications due to its porous nature.
Symbolism and Metaphysical Beliefs
Opal is associated with several symbolic meanings and metaphysical properties. It is believed to strengthen memory, foster originality, and increase energy levels. The stone is also thought to aid in self-expression and help individuals understand their full potential.
Beyond these general benefits, specific colors of opal are believed to possess unique properties. Blue opal, for example, is said to symbolize serenity, balance, and self-confidence. Yellow opal is thought to exude a joyful, optimistic, and confident energy.
Care and Cleaning
Due to its relatively delicate nature, opal requires careful handling and cleaning. While the sources do not provide specific hardness data, it is understood that opal is susceptible to scratching and damage. It is advisable to avoid harsh chemicals, ultrasonic cleaners, and extreme temperature changes. Cleaning can be performed with a soft cloth and lukewarm soapy water.
Conclusion
Opal remains a captivating gemstone, cherished for its unique play-of-color, rich history, and symbolic significance. From its ancient origins to its modern status as a beloved birthstone, opal continues to inspire awe and wonder. Its diverse varieties, geological formations, and metaphysical properties contribute to its enduring appeal, making it a prized possession for gemstone enthusiasts and a meaningful gift for those born in October.