October is uniquely blessed with not one, but two recognized birthstones: opal and tourmaline. Both gemstones offer a stunning array of colors and captivating optical phenomena, making them popular choices for jewelry and collectors alike. While opal historically held the sole designation as October’s birthstone, tourmaline was added in 1912, offering a wider range of options and reflecting evolving tastes in gemology. This article will explore the history, geological origins, gemological properties, symbolism, and care of these two remarkable gemstones.
History and Lore
The story of opal dates back to ancient times. Its origins are believed to lie in India, where it was known as Upala, meaning “precious stone.” The Romans referred to it as opalus, and it was highly prized for its unique play-of-color. Ancient Greeks believed opal bestowed the power of prophecy and protected its wearer from disease. In Europe, opal became associated with purity, hope, and truth, and was considered to embody the virtues of all colored stones. Bedouins even believed opals contained lightning and fell from the sky during thunderstorms.
Tourmaline’s history is somewhat more complex, as its diverse colors often led to misidentification with other gemstones. Green tourmaline crystals discovered in Brazil by Spanish conquistadors in the 1500s were initially mistaken for emeralds. It wasn’t until the 19th century that tourmaline was formally recognized as a distinct mineral species. A notable example of this historical confusion is the “Caesar’s Ruby” in the Russian crown jewels, which is, in fact, a red tourmaline (rubellite).
The standardization of birthstone lists began in 1912 with the National Association of Jewellers, which designated opal as the primary October birthstone and tourmaline as an alternative. This decision was partly influenced by a desire to offer more options, as some considered opal too feminine or questioned its durability. The National Association of Jewellers further standardized the list in 1952, modifying it as styles and availability of stones changed over time.
Geological Formation and Sources
Opals are formed from silica-rich water that seeps into cracks and voids in the earth. As the water evaporates, it leaves behind microscopic spheres of silica. The size and arrangement of these spheres determine the type of opal and the play-of-color it exhibits. Precious opals, known for their vibrant displays of color, are relatively rare and are primarily found in Australia, which accounts for the vast majority of the world’s supply. Other sources include Ethiopia, Mexico, and the United States.
Tourmaline, on the other hand, forms in igneous and metamorphic rocks, often in pegmatites – coarse-grained igneous rocks. Its chemical composition is complex, involving boron, aluminum, and various other elements, which contribute to its wide range of colors. Tourmaline is found in numerous locations worldwide, including Brazil, Africa, Afghanistan, Pakistan, and the United States. Pink and red tourmalines (rubellites) are particularly sought after, as are the vibrant green and blue “paraiba” tourmalines, discovered in Brazil and later in Mozambique and Nigeria.
Gemological Properties
Opal is an amorphous mineral, meaning it lacks a defined crystalline structure. Its hardness ranges from 5.5 to 6.5 on the Mohs scale, making it relatively soft and susceptible to scratching. The defining characteristic of opal is its “play-of-color,” a mesmerizing display of iridescent hues caused by the diffraction of light through the silica spheres.
Tourmaline, in contrast, is a crystalline mineral with a hardness of 7 to 7.5 on the Mohs scale, making it more durable than opal. Its chemical formula is complex, varying depending on the specific type of tourmaline. The different chemical compositions result in a wide spectrum of colors, including pink, red, green, blue, and even colorless. Tourmaline exhibits strong pleochroism, meaning it displays different colors when viewed from different angles.
Here's a comparative table summarizing key gemological properties:
| Property | Opal | Tourmaline |
|---|---|---|
| Chemical Formula | SiO₂·nH₂O | (Na,Ca)(Al,Li,Mg)₃(Al,Fe,Mn)₆(BO₃)₃(Si₆O₁₈)(OH)₄ |
| Hardness (Mohs) | 5.5 - 6.5 | 7 - 7.5 |
| Crystal System | Amorphous | Trigonal |
| Specific Gravity | 1.98 - 2.15 | 3.06 - 3.10 |
| Luster | Vitreous | Vitreous |
| Key Characteristic | Play-of-Color | Pleochroism |
Symbolism and Metaphysical Beliefs
Throughout history, both opal and tourmaline have been attributed with various symbolic meanings and metaphysical properties. Opal has long been associated with hope, purity, and truth. Ancient Greeks believed it could bestow prophetic powers, while Bedouins linked it to lightning and divine intervention.
Tourmaline’s symbolism varies depending on its color. Black tourmaline is believed to protect against negativity and enhance self-confidence. Pink tourmaline is associated with compassion, love, and emotional healing. Green tourmaline is thought to promote courage, strength, and stamina. The eighth wedding anniversary is traditionally celebrated with a gift of tourmaline.
Care and Cleaning
Due to its relatively low hardness, opal requires careful handling and cleaning. It is susceptible to scratching and should be protected from impacts. Opal should be cleaned with a soft cloth and mild soapy water. Avoid harsh chemicals, ultrasonic cleaners, and prolonged exposure to heat or sunlight, as these can cause cracking or fading.
Tourmaline is more durable than opal and can withstand more rigorous cleaning. It can be cleaned with warm soapy water and a soft brush. Ultrasonic cleaners are generally safe for tourmaline, but caution should be exercised with stones that have been fracture-filled.
Conclusion
Opal and tourmaline, the captivating birthstones of October, offer a diverse range of colors, histories, and symbolic meanings. From the ancient lore surrounding opal’s play-of-color to the complex geological origins of tourmaline’s vibrant hues, these gemstones continue to fascinate and inspire. Whether chosen for their beauty, their metaphysical properties, or their historical significance, opal and tourmaline are truly exceptional gems.