The October birthstone, Opal, is a gemstone of extraordinary beauty and a rich tapestry of historical and cultural significance. Unlike many gemstones that derive their allure from a single dominant color, opal is renowned for its play-of-color—a phenomenon in which the stone displays a shifting spectrum of colors, often described as a "rainbow in the stone." This unique optical property has made opal a gemstone of fascination for millennia, and its journey from ancient lore to modern symbolism as the October birthstone is a compelling one.
This article explores the geological origins and properties of opal, its historical and cultural significance, and its contemporary role as the October birthstone. We will also examine how opal has been perceived across different eras—both as a symbol of hope and a harbinger of misfortune—and what these beliefs reveal about the enduring human fascination with this enigmatic gemstone.
History and Lore
Ancient Beliefs and Cultural Significance
The history of opal is intertwined with the myths and legends of ancient civilizations. The name "opal" is derived from the Greek word "opalinus," meaning "to see a changing color," a reference to the gemstone’s iridescent properties. The Roman poet Pliny the Elder (23–79 CE) famously described opal as the "queen of gems," praising its ability to display all the colors of the rainbow.
In ancient Rome, opal was believed to bring good fortune and protection. Roman soldiers would carry opal into battle to ensure victory and safe return. Roman women, particularly those of noble birth, often wore opal in jewelry, believing it would enhance their beauty and allure. Pliny also noted that opal was considered a versatile gem, combining the virtues of all other gemstones.
In Persian and Indian cultures, opal was regarded with a mix of awe and reverence. Persian mystics believed opal held divine power, and it was often used in talismans and amulets to ward off evil spirits. In India, opal was considered a stone of prophecy, used by astrologers to interpret the future.
Opal in the Middle Ages and Renaissance
During the Middle Ages, the perception of opal began to shift. In some parts of Europe, particularly in England, opal was regarded with suspicion. Superstitions arose that linked opal to bad luck, especially if the stone lost its color or cracked. This negative perception was partly fueled by Shakespeare, who in his play Hamlet (1600) wrote:
"There's something in it that is not natural, if this were play'd upon a stage now, I could condemn it as an improbable fiction."
Although the reference is often misinterpreted, it contributed to the idea that opal was an unnatural or uncanny gem. The English author Sir Walter Scott further cemented this belief by calling opal the "stone of hope" and "the most precious of gems," but only if it was found in the right place and under the right conditions.
Despite this, opal remained popular in France and Italy, where it was used in fine jewelry and religious artifacts. In the Renaissance, opal was often included in engagement rings and mystical amulets, symbolizing love, passion, and the mysteries of the universe.
The 19th and 20th Centuries
The 19th century marked a resurgence of interest in opal, particularly in Australia, which became the world’s largest producer. The discovery of light opal in New South Wales (1872) and boulder opal in Queensland (1880) brought opal into the global spotlight. Australian opal quickly became the most sought-after variety, known for its vibrant colors and exceptional clarity.
During the Victorian era, opal was used in fashionable jewelry, particularly in lockets, brooches, and pendants. The British royal family was known to wear opal jewelry, and the Queen Victoria herself owned several opal pieces, including a famous opal brooch gifted by her husband, Prince Albert.
By the early 20th century, opal had gained a new kind of cultural significance. It was associated with mysticism and spirituality, and in New Age movements, it was considered a stone of transformation, creativity, and emotional healing. These beliefs helped to shift the perception of opal from a symbol of bad luck to one of positive energy and renewal.
Geological Formation and Sources
How Opal is Formed
Opal is a hydrous amorphous form of silica, meaning it is composed primarily of silicon dioxide (SiO₂) and contains a significant amount of water—typically between 6% and 20% by weight. Unlike crystalline gemstones such as diamonds or rubies, opal does not have a defined crystal structure. Instead, it is composed of microscopic spheres of silica that are arranged in a three-dimensional lattice. These spheres are typically 100–300 nanometers in diameter and are spaced in a way that allows light to diffract, producing the play-of-color effect.
The formation of opal occurs over millions of years through a process known as diagenesis. This process begins when silica-rich water seeps through the pores of sedimentary rocks. As the water evaporates, it leaves behind silica deposits, which gradually accumulate and solidify into opal. The presence of iron and other minerals can influence the color and opacity of the final gemstone.
There are two main types of opal:
- Common Opal: Lacks the play-of-color and is usually opaque or translucent. It is less valuable than precious opal.
- Precious Opal: Displays the play-of-color effect and is the most prized variety.
Major Sources of Opal
The most important source of opal is Australia, which produces approximately 90% of the world’s opal. The major opal fields in Australia include:
- Light Opal (White Opal): Found in New South Wales, particularly in Andamooka, Coober Pedy, and Koroit. This variety has a white or light background and displays vivid colors.
- Black Opal: Found in New South Wales, especially in Lightning Ridge. This opal has a dark body tone, which enhances the vibrancy of the play-of-color.
- Boulder Opal: Found in Queensland, especially in Yowah, Blackstone, and Gawler Ranges. This opal forms within ironstone boulders and is often more durable than other types.
- Doublets and Triplets: These are man-made composite stones that combine a thin slice of opal with a base of onyx or black glass (doublet) or a resin top layer (triplet). They are used to create more affordable opal jewelry.
Other notable opal sources include:
- Mexico: Known for fire opal, which is usually translucent yellow or orange and lacks the play-of-color.
- Ethiopia: Discovered in the late 20th century, Ethiopian opal is known for its high water content and vibrant colors.
- Brazil: Produces hyalite opal, which is colorless and translucent.
- United States: Opal is found in Idaho, Nevada, and Oregon, but in much smaller quantities.
Gemological Properties
Physical and Optical Characteristics
Opal is a soft gemstone, ranking between 5 and 6.5 on the Mohs scale of hardness. This relatively low hardness means that opal is susceptible to scratches and abrasions, especially if it is porous or contains inclusions. Because of this, opal is best suited for pendants, earrings, and brooches, rather than rings and bracelets, where it is more likely to be subjected to friction and impact.
The refractive index of opal is 1.37 to 1.50, and its specific gravity (density) ranges from 1.9 to 2.3, depending on the water content. Opal is also thermally sensitive, meaning it can crack or lose luster if exposed to high heat or rapid temperature changes. This is why it is important to avoid exposing opal to direct sunlight or heat sources for extended periods.
Color and Play-of-Color
One of the most distinctive features of opal is its play-of-color, a phenomenon caused by the diffraction of light through the silica spheres in the stone. The colors seen in opal are not surface reflections, as in a mirror, but rather internal interference patterns, similar to those seen in oil slicks or soap bubbles.
The colors in opal are typically green, blue, violet, orange, and red, and they can shift depending on the angle of light and the viewer's perspective. This effect is most prominent in precious opal, especially in black opal, where the dark background enhances the vividness of the colors.
Treatments and Enhancements
Because of its softness and porosity, opal is often treated or enhanced to improve its durability and appearance. Common treatments include:
- Impregnation with resins or oils: This fills the pores in the opal, making it less brittle and more stable.
- Heating: Used to enhance the color of certain opals, though it can also alter the play-of-color.
- Doublets and triplets: As mentioned earlier, these are composite stones that combine thin slices of opal with other materials to create a more durable and affordable product.
It is important to note that all treatments should be disclosed by the seller or jeweler, as they can significantly affect the value and appearance of the gemstone.
Symbolism and Metaphysical Beliefs
Historical and Cultural Symbolism
Throughout history, opal has been associated with a wide range of symbolic meanings, often reflecting the values and beliefs of the cultures that valued it. In ancient Rome, opal was considered a stone of good fortune and was believed to combine the virtues of all other gemstones. Roman soldiers would carry opal into battle to ensure victory and protection, and Roman women believed it enhanced beauty and allure.
In Persian and Indian cultures, opal was seen as a stone of prophecy and divine power. Persian mystics used opal in talismans and amulets, believing it could ward off evil spirits and bring wisdom. In India, opal was considered a stone of transformation, used by astrologers and mystics to interpret the future.
During the Middle Ages, opal’s reputation in Europe became more complex. While it was still used in fine jewelry and religious artifacts, it was also associated with superstition. Some believed that losing the play-of-color in an opal was a sign of bad luck, and others thought that cracking or breaking the stone could bring misfortune. This belief was reinforced by Shakespeare and Sir Walter Scott, both of whom wrote about opal in a way that suggested it was unpredictable and mysterious.
Modern Metaphysical and Spiritual Beliefs
In modern times, opal has regained its status as a stone of positive energy and transformation. It is often associated with emotional healing, creativity, and spiritual growth. In New Age and crystal healing communities, opal is believed to:
- Enhance creativity and imagination
- Promote emotional balance and stability
- Stimulate spiritual insight and intuition
- Protect against negative energies
- Support the healing of emotional wounds
Opal is also considered a stone of change, making it a popular choice for those undergoing personal transformation or major life transitions. It is believed to help individuals navigate uncertainty and find clarity and direction in times of change.
In jewelry design, opal is often used in engagement rings and wedding bands, symbolizing love, passion, and the unpredictable nature of relationships. It is also used in fashion and statement jewelry, where its iridescent beauty makes a bold and eye-catching statement.
Care and Cleaning
Cleaning and Maintenance
Due to its softness and porosity, opal requires special care to maintain its beauty and durability. Here are some best practices for cleaning and caring for opal:
- Avoid exposure to heat and direct sunlight: Opal contains a significant amount of water, and prolonged exposure to high heat or sunlight can cause it to dry out, crack, or lose luster.
- Avoid harsh chemicals: Opal is sensitive to acids, alkalis, and solvents, which can damage the surface or alter the play-of-color. This includes household cleaners, perfumes, and lotions.
- Clean with care: Use a soft cloth or a mild soap and water solution to clean opal. Avoid ultrasonic or steam cleaners, as they can damage the stone.
- Store properly: Store opal in a soft pouch or a separate compartment to prevent scratches from harder gemstones. It is also a good idea to store opal in a cool, dry place to prevent it from drying out.
- Avoid abrasive materials: Opal can be easily scratched, so avoid using abrasive cloths, brushes, or polishing agents.
Repair and Reconditioning
If opal becomes cracked, chipped, or discolored, it may be possible to repair or recondition it, depending on the extent of the damage. Minor cracks can be filled with a clear resin to prevent further damage and restore the appearance. However, this is a delicate process that should be done by a qualified gemologist or jeweler.
In cases where the play-of-color has faded, it may be possible to rehydrate the stone by placing it in a sealed container with a damp cloth or silica gel. This process should be done with care and patience, as over-saturation can damage the stone.
Conclusion
Opal, the October birthstone, is a gemstone of extraordinary beauty and historical significance. Its play-of-color effect has fascinated people for centuries, and its symbolism as a stone of transformation, creativity, and emotional healing has made it a valuable gemstone in both historical and modern contexts.
From its geological origins in sedimentary rock to its cultural significance in ancient Rome and Persia, opal has played a unique role in human history. While it has faced periods of superstition and fear, especially in medieval Europe, it has also been celebrated as a symbol of hope, beauty, and spiritual insight.
Today, opal continues to be highly valued in the gem and jewelry trade, particularly in Australia, where it is the most abundant and beautiful variety in the world. Whether worn as a jewelry piece, a spiritual tool, or a symbol of personal transformation, opal remains a gemstone of enduring fascination and significance.