Opal, the luminous and iridescent gemstone of October, captivates with its unique play-of-color—a kaleidoscopic display that seems to capture the very essence of light and fire. As one of the two official birthstones for the tenth month (alongside tourmaline), opal has a history as deep and varied as the colors that dance within its body. This article delves into the rich tapestry of opal, exploring its historical significance, geological origins, distinctive gemological properties, and the metaphysical beliefs that have surrounded it for millennia. From ancient Egyptian tombs to modern jewelry boxes, opal’s journey through human culture is a testament to its enduring allure and enigmatic beauty.
History and Lore
The history of opal is intertwined with the very concept of birthstones, which itself dates back to ancient civilizations. The belief that specific gemstones hold power and meaning associated with the month of one's birth can be traced to cultures such as the Egyptians, Greeks, and Romans. These societies believed each gemstone possessed special properties linked to the month of a person's birth. A pivotal moment in the history of birthstones is found in the Book of Exodus, which describes a breastplate worn by Aaron, the first high priest of the Israelites. This breastplate was adorned with 12 different stones, each representing one of the 12 tribes of Israel. These stones were believed to possess great powers and had the ability to reveal people’s destinies. The exact gems used in Aaron’s breastplate are somewhat uncertain due to the naming conventions of the time, which were based on color rather than chemical composition.
Approximately 500 years after Aaron's breastplate, the historian Josephus believed there was a connection between the 12 stones in the breastplate, the 12 months of the year, and the 12 zodiac signs. This idea was further developed in the 5th century by St. Jerome, who suggested a link between the stones and the months. However, the systematic assignment of a single birthstone to each month is a more modern convention. The list was standardized in 1912 by the American National Retail Jewelers Association (now known as Jewelers of America). This list assigns a specific gemstone to each month of the year, with each stone believed to bring luck, protection, and other benefits to those born in that month. For October, opal was officially designated as the primary birthstone.
Throughout history, birthstones have been used for various purposes, including jewelry adornment, healing practices, and astrological significance. Opal, in particular, has a storied past. In ancient Rome, it was considered the most powerful and precious gem, symbolizing hope and purity. The Romans believed opal contained the powers of all colored gemstones, making it the "Queen of Gems." During the Middle Ages, opal was thought to be a talisman for the eyes, protecting against poor vision and evil spirits. Its reputation shifted dramatically in the late 19th century, largely due to a fictional work. Sir Walter Scott's novel Anne of Geierstein (1829) featured a cursed opal, which led to a significant decline in opal's popularity across Europe. This superstition, though based on a work of fiction, persisted for decades.
Despite this setback, opal's allure never fully waned. It experienced a revival in the 20th century, especially with the discovery of vast opal deposits in Australia. Today, opal continues to hold cultural significance and is cherished as a meaningful gift for birthdays and other special occasions. Its status as a birthstone allows individuals to connect with the gem's rich history and the personal significance of their birth month.
Geological Formation and Sources
Opal is not a crystal like many other gemstones; it is a mineraloid, meaning it lacks a crystalline structure. It is composed of hydrated silica (SiO₂·nH₂O), with water content typically ranging from 3% to 21%. The formation of opal is a geological process that occurs in areas where silica-rich water seeps into cracks and voids in the earth. Over millions of years, as the water evaporates, the silica is deposited in the form of microscopic spheres. The size and arrangement of these spheres are critical to opal's appearance. In precious opal, the spheres are uniform in size and packed in a regular, three-dimensional pattern, which diffracts light to produce the characteristic play-of-color. Common opal, which lacks this structure, displays a single, uniform color.
Opal is found in several locations worldwide, but Australia is the undisputed leader in production and quality. Australian opal is renowned for its vivid play-of-color and is often considered the benchmark for the gem. Major Australian opal fields include Lightning Ridge in New South Wales, known for its black opal (the most valuable type, with a dark body tone), and Coober Pedy in South Australia, famous for its crystal and white opals. The Andamooka field in South Australia also produces significant quantities of opal.
Other notable sources of opal include Ethiopia, which has emerged as a major producer in recent years, particularly of hydrophane opal—a variety that can absorb water and temporarily lose its play-of-color. Mexico is known for its fire opal, which is typically transparent to translucent and exhibits a warm body color of orange, red, or yellow, sometimes with play-of-color. Brazil, Peru, and the United States (notably Nevada) also contribute to the global opal supply, though in smaller quantities.
The mining of opal is a challenging and often unpredictable endeavor. It typically involves excavating in arid or semi-arid regions, where opal-bearing strata are located. Miners must carefully extract the rough material, which is often fragile, and then assess its potential for cutting. The yield of gem-quality opal from rough material is often low, contributing to its value.
Gemological Properties
Opal possesses a unique set of properties that distinguish it from other gemstones. Its most celebrated characteristic is play-of-color, a phenomenon where flashes of spectral color appear and change as the viewing angle changes. This is caused by the diffraction of light by the silica spheres within the gem. The most prized play-of-color displays the full spectrum of the rainbow, including red, orange, yellow, green, blue, indigo, and violet. The body color of opal (the background color) can range from colorless (white) to black, with various shades of gray, brown, orange, and red in between.
Other key gemological properties of opal include:
- Hardness: Opal has a hardness of 5.5 to 6.5 on the Mohs scale, making it relatively soft compared to many other gemstones. This means it is susceptible to scratching and abrasion and should be handled with care.
- Luster: Opal exhibits a vitreous (glass-like) to resinous luster, which contributes to its captivating appearance.
- Refractive Index: The refractive index of opal typically ranges from 1.37 to 1.45.
- Specific Gravity: The specific gravity of opal varies between 1.98 and 2.20.
- Transparency: Opal can be transparent, translucent, or opaque, depending on the variety.
- Crystal System: Opal is amorphous, meaning it does not have a regular crystalline structure.
The following table summarizes the key gemological properties of opal:
| Property | Value / Description |
|---|---|
| Chemical Formula | SiO₂·nH₂O (Hydrated Silica) |
| Hardness (Mohs) | 5.5 - 6.5 |
| Refractive Index | 1.37 - 1.45 |
| Specific Gravity | 1.98 - 2.20 |
| Luster | Vitreous to Resinous |
| Crystal System | Amorphous |
| Transparency | Transparent to Opaque |
Different varieties of opal are classified based on their body color and play-of-color. White opal has a light body color and displays play-of-color. Black opal has a dark body tone (gray to black), which makes the play-of-color appear more vibrant. Crystal opal is transparent to translucent with a clear body, allowing light to pass through and enhancing the play-of-color. Fire opal is prized for its warm body color, often orange or red, and may or may not exhibit play-of-color. Boulder opal is a thin layer of opal attached to its ironstone host rock, which is often part of the final gem. Matrix opal is a type where the opal fills the pores or cracks in a host rock.
Symbolism and Metaphysical Beliefs
Opal has been surrounded by a rich tapestry of symbolism and metaphysical beliefs throughout history. Its iridescent nature has led it to be associated with transformation, creativity, and emotional expression. In ancient times, it was often linked to the powers of prophecy and was believed to reveal the wearer's future. The Romans considered it the symbol of hope and love, and it was thought to grant the wearer the ability to see the future and protect them from disease.
In the Middle Ages, opal was called the "Eye Stone" and was believed to improve eyesight and protect against evil spirits. It was also associated with the concept of purity and was often used in religious jewelry. The gem's play-of-color, which seems to capture the essence of all other gemstones, led to the belief that it contained the powers of each stone in the birthstone chart.
In modern metaphysical circles, opal is often associated with emotional balance and creativity. It is believed to stimulate inspiration, enhance creativity, and help the wearer express their true self. Some believe that opal can help release past traumas and promote emotional healing. It is also associated with the concept of "light," both literal and metaphorical, and is thought to bring joy and optimism to the wearer.
It is important to note that many of these beliefs are rooted in tradition and folklore rather than scientific evidence. However, they add a layer of cultural and personal significance to the gemstone, making it a meaningful choice for jewelry and gifts. For those born in October, wearing opal is seen as a way to tap into these symbolic meanings and connect with the unique energy of their birth month.
Care and Cleaning
Given opal's relative softness and sensitivity to changes in moisture, proper care is essential to maintain its beauty and integrity. With a hardness of 5.5 to 6.5, opal can be easily scratched by harder materials, including other gemstones, dust, and even sand. Therefore, it should be stored separately from other jewelry, preferably in a soft cloth pouch or a lined jewelry box.
Cleaning opal requires gentle methods. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals, as these can damage the stone or cause it to crack due to thermal shock or exposure to solvents. The best way to clean opal is with a soft, lint-free cloth slightly dampened with lukewarm water. Gently wipe the surface to remove dirt and oils. After cleaning, dry the gemstone thoroughly with a soft, dry cloth.
For opals that are set in jewelry, especially rings, extra caution is advised. Due to the softness and potential for chipping, it is not recommended to wear opal rings during activities that could subject them to impact or abrasion, such as gardening, sports, or heavy manual work. It is also important to be mindful of the environment. Extreme temperature changes and prolonged exposure to direct sunlight can cause opal to lose water and develop cracks, a phenomenon known as "crazing." While this is more common in untreated opals, it is still a risk to be aware of.
Hydrophane opal, which is porous and can absorb water, requires special attention. When it absorbs water, it may temporarily become cloudy or lose its play-of-color. This effect is usually reversible, and the opal will return to its original state as it dries out. However, it is advisable to avoid exposing hydrophane opal to excessive moisture or chemicals that could be absorbed into its structure.
By following these simple care guidelines, the beauty and vibrancy of an opal can be preserved for generations, allowing it to continue its role as a cherished gemstone and a symbol of October.
Conclusion
Opal stands as a gemstone of remarkable complexity and beauty, bridging the gap between ancient lore and modern science. Its designation as a birthstone for October is rooted in a tradition that spans millennia, from the breastplate of Aaron to the standardized charts of the 20th century. The gem's geological formation as a hydrated silica mineraloid, resulting in the mesmerizing play-of-color, makes it unique among precious stones. While its relatively soft nature requires careful handling, the proper care ensures that its iridescent display can be enjoyed for a lifetime. Whether appreciated for its scientific wonder, historical significance, or metaphysical symbolism, opal continues to captivate gemstone enthusiasts, jewelry buyers, and students of gemology alike. It remains a timeless emblem of creativity, hope, and the luminous beauty found within the earth.