October boasts the unique distinction of having two recognized birthstones: opal and tourmaline. Both gems offer a dazzling spectrum of colors and a rich history, making them popular choices for jewelry and collectors alike. While opal holds the position as the traditional October birthstone, tourmaline has gained prominence as a modern alternative, offering a wider range of hues and a fascinating geological story. This article will delve into the history, geological origins, gemological properties, symbolism, and care of these captivating gemstones.
History and Lore
The story of opal begins in India, where the earliest opals were sourced and prized. The Sanskrit word upala, meaning “precious stone,” is believed to be the origin of the gem’s name. This evolved into opalus in ancient Rome. Throughout history, opal has been associated with various beliefs. Ancient Greeks believed the stone bestowed the gift of prophecy and offered protection from disease. In Europe, opal was long considered a symbol of purity, hope, and truth, and was once thought to embody the virtues of all colored stones. It is also the traditional gem given to celebrate a 14th wedding anniversary.
Tourmaline’s history is somewhat different. Its name originates from the Sinhalese word toramalli, meaning “stone with mixed colors,” a fitting description given the gem’s remarkable pleochroism and variety of shades. For centuries, tourmaline was often mistaken for other gemstones, including ruby and emerald. A notable example is the “Caesar’s Ruby” in the Russian crown jewels, which is, in fact, a red tourmaline (rubellite). It wasn’t until the 19th century that scientists recognized tourmaline as a distinct mineral species. Ancient mystics believed tourmaline could inspire artistic expression, owing to its diverse color palette. It is traditionally given to celebrate an 8th wedding anniversary.
The association of specific gemstones with birth months is a practice that evolved over time. Initially, the twelve gemstones in the breastplate of Aaron in biblical times were linked to the twelve tribes of Israel. Later, connections were made between these gems and the signs of the zodiac. The modern practice of assigning one gem to each month emerged between the 16th and 18th centuries, with the National Association of Jewelers releasing a standardized list of “modern birthstones” in 1912.
Geological Formation and Sources
Opal is unique in its formation. Unlike many gemstones that crystallize, opal is a hydrated amorphous form of silica. It forms in cracks and voids in the earth, typically in sedimentary environments. Hot silica-rich solutions seep into these spaces, and as the water evaporates, it leaves behind deposits of silica spheres. The arrangement of these spheres determines the “play-of-color” that makes opal so prized.
Australia is the world’s leading source of opal, particularly the rare black opal found in Lightning Ridge, New South Wales. White opal is found in areas like White Cliffs in New South Wales, and Mintabie and Coober Pedy in South Australia. Boulder opal is exclusively mined in Queensland, forming within ironstone boulders. Beyond Australia, significant opal deposits are found in Ethiopia, specifically near Wegel Tena in Wollo Province, and in Querétaro, Mexico, which is known for its fire opal.
Tourmaline forms in igneous and metamorphic rocks, often in pegmatites – coarse-grained igneous rocks. Its chemical composition is complex, involving boron, silicon, aluminum, and various other elements, which contribute to its wide range of colors. Tourmaline is found in numerous locations worldwide, though specific color varieties are associated with particular regions.
Gemological Properties
Opal: Opal’s defining characteristic is its play-of-color, a shimmering display of rainbow hues caused by the diffraction of light through microscopic silica spheres. It has a hardness of 5.5-6.5 on the Mohs scale, making it relatively soft and susceptible to scratching. Its specific gravity ranges from 1.98 to 2.15. Opal contains approximately 3-21% water, which can affect its stability.
Tourmaline: Tourmaline is a complex borosilicate mineral with a hardness of 7-7.5 on the Mohs scale, making it more durable than opal. Its specific gravity ranges from 3.02 to 3.34. Tourmaline exhibits strong pleochroism, meaning it displays different colors when viewed from different angles. The gem’s color is determined by its chemical composition, with various elements contributing to the wide range of hues. Common varieties include:
- Rubellite: Red to pink tourmaline
- Chrome Tourmaline: Emerald green tourmaline
- Paraíba Tourmaline: Neon green to blue-to-violet tourmaline, highly valued for its vivid color.
Here's a table summarizing the key gemological properties:
| Property | Opal | Tourmaline |
|---|---|---|
| Hardness (Mohs) | 5.5-6.5 | 7-7.5 |
| Specific Gravity | 1.98-2.15 | 3.02-3.34 |
| Chemical Formula | SiO₂·nH₂O | Complex Borosilicate |
| Play-of-Color | Present | Absent |
| Pleochroism | Weak | Strong |
Symbolism and Metaphysical Beliefs
Throughout history, both opal and tourmaline have been attributed with various symbolic meanings and metaphysical properties. Opal has been associated with hope, purity, and truth, and was believed to bestow prophetic abilities and protection from disease.
Tourmaline’s symbolism varies depending on its color. Black tourmaline is believed to offer protection and promote self-confidence. Pink tourmaline is associated with love, compassion, and gentleness. Green tourmaline is thought to encourage courage, strength, and stamina. The diverse colors of tourmaline contribute to its reputation as a stone that can inspire artistic expression and balance emotions.
Care and Cleaning
Due to its relatively low hardness, opal requires careful handling. It is susceptible to scratching and can be damaged by sudden temperature changes or prolonged exposure to dry heat, which can cause it to crack. Opal should be cleaned with a soft cloth and mild soapy water. Avoid ultrasonic cleaners and harsh chemicals.
Tourmaline is more durable than opal and can withstand more rigorous cleaning. It can be cleaned with warm soapy water, a soft brush, and a polishing cloth. Ultrasonic cleaners are generally safe for tourmaline, but avoid using them for stones that have been fracture-filled.
Conclusion
Opal and tourmaline, the captivating birthstones of October, offer a vibrant array of colors, rich histories, and fascinating geological origins. Opal, with its ethereal play-of-color, has been cherished for centuries as a symbol of hope and inspiration. Tourmaline, with its diverse hues and complex composition, represents artistic expression and emotional balance. Both gemstones continue to captivate jewelry lovers and gem enthusiasts alike, solidifying their place as treasured symbols of the October birth month.