The month of December is uniquely associated with three distinct gemstones: the ancient sky-blue turquoise, the vivid violet-blue tanzanite, and the multifaceted zircon. Each carries its own history, geological story, and symbolic weight, offering December-born individuals a spectrum of choices. This article delves into the characteristics, origins, and significance of these three December birthstones, providing a comprehensive guide for gemstone enthusiasts and jewelry buyers.
Introduction
December is one of the few months with multiple official birthstones, a designation that reflects both historical tradition and modern gemological discovery. The traditional birthstone for December is turquoise, a gem revered for millennia for its distinctive robin's egg blue hue. In 1912, the National Association of Jewellers in the United States standardized the list of birthstones, establishing turquoise as the official December stone. However, the list was updated in 2002 by the American Gem Trade Association (AGTA) to include tanzanite, and again in 2016 to include zircon, giving December-born individuals a broader palette of colors and properties to celebrate their birth month.
This article explores the rich tapestry of these three stones. We will examine the deep history and lore of turquoise, the modern geological marvel of tanzanite, and the often-misunderstood brilliance of zircon. From ancient Egyptian tombs to contemporary jewelry settings, these gemstones represent a fascinating convergence of geology, history, and human culture.
History and Lore: From Ancient Amulets to Modern Gems
Turquoise: The Stone of the Sky
Turquoise is among the earliest gemstones mined and used by humans. Its history spans continents and civilizations, consistently associated with protection, wisdom, and good fortune. Ancient Egyptians mined turquoise in the Sinai Peninsula as early as 6000 BCE, using it to create intricate jewelry, amulets, and inlays for objects of power. The famous burial mask of Tutankhamun is adorned with turquoise, symbolizing the pharaoh's connection to the divine and the afterlife.
In the American Southwest, Native American tribes such as the Navajo, Zuni, and Pueblo peoples have a profound spiritual connection to turquoise. For centuries, they have mined the stone from regions like Arizona and New Mexico, crafting it into jewelry that is both decorative and ceremonial. To these cultures, turquoise represents the sky, water, and earth, and is believed to offer protection and healing.
Across the globe, Persian turquoise was highly prized for its intense sky-blue color, often free of matrix (the host rock). In the Middle East and Central Asia, turquoise was worn as a talisman to ward off the "evil eye" and bring safety during travel. The stone's name itself derives from the French "pierre tourques," meaning "Turkish stone," as it was brought to Europe from Turkey via Persian trade routes.
Tanzanite: The Gem of a Single Source
In stark contrast to turquoise's ancient pedigree, tanzanite is a newcomer to the gemological world. Its discovery is a modern geological tale. In 1967, a prospector named Manuel de Souza discovered a cluster of transparent blue crystals near the base of Mount Kilimanjaro in Tanzania. Initially thought to be an unusual variety of sapphire, further analysis by the Gemological Institute of America (GIA) in 1967 identified it as a previously unknown variety of the mineral zoisite.
The gem's unique violet-blue color, which can range from ultramarine to pale lavender, is the result of heat treatment, which removes brownish-yellow impurities and enhances the blue hue. Tiffany & Co. recognized its potential and launched a major marketing campaign in 1968, naming it "tanzanite" after its country of origin. Due to its exclusive source—a single mining area in the Merelani Hills of northern Tanzania—tanzanite is often described as "a million times rarer than diamond." While it is not the official birthstone for any month in the traditional sense, its inclusion in the December list reflects its popularity and stunning color.
Zircon: The Color-Changing Stone
Zircon is one of the oldest minerals on Earth, with crystals dating back over 4 billion years. Its name is derived from the Persian word "zargun," meaning "gold-colored," though the gem is most prized for its fiery brilliance and colorless varieties that rival diamonds. For centuries, zircon has been confused with cubic zirconia, a synthetic diamond simulant, leading to some misunderstanding of its value. However, natural zircon is a distinct and valuable gemstone with exceptional refractive index and dispersion (fire).
In the Middle Ages, zircon was believed to promote sleep, ward off evil spirits, and bring prosperity. The stone is also associated with wisdom and honor. Colorless zircon was particularly popular during the Victorian era as a diamond alternative. In 2016, the American Gem Trade Association added zircon as a third birthstone for December, recognizing its durability (in its most stable forms) and its wide range of desirable colors, including blue, yellow, brown, and red.
Geological Formation and Sources
Turquoise: A Hydrated Phosphate Mineral
Turquoise is not a silicate mineral like most gemstones; it is a hydrated phosphate of copper and aluminum, with the chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O. It forms in arid regions where acidic, copper-rich groundwater percolates through rocks containing aluminum and phosphorus. Over millions of years, these minerals precipitate and solidify into turquoise, often filling fractures and voids in the host rock. The presence of copper gives turquoise its characteristic blue color, while iron can create greenish tones.
Major sources of turquoise include: - Iran (Persia): Historically the most significant source of high-quality, sky-blue turquoise with minimal matrix. - United States: The Southwestern states, particularly Arizona, Nevada, and New Mexico, produce a vast array of turquoise varieties, often characterized by a matrix (the host rock) that creates unique patterns (e.g., "spiderweb" matrix). - China: A major producer of turquoise, often with a more porous structure and vibrant colors. - Egypt, Afghanistan, and Mexico: Also have significant turquoise deposits.
Tanzanite: A Single-Source Gemstone
Tanzanite is a variety of the mineral zoisite, specifically the blue to violet-blue form. Its chemical formula is Ca₂Al₃(SiO₄)₃(OH). It forms in the metamorphic rocks of the East African Rift, a geological feature created by the movement of tectonic plates. The unique conditions in the Merelani Hills—specifically, the presence of the right minerals under specific heat and pressure—are responsible for creating tanzanite. No other location on Earth has been found to produce gem-quality tanzanite, making its supply finite.
Mining occurs in four small, distinct areas (Blocks A, B, C, and D) in the Merelani Hills. Block C is the most famous, producing the finest "blue" material. The mining is often done on a small scale, with challenges related to environmental impact and ethical sourcing. The exclusivity of its source contributes to its value and appeal.
Zircon: A Resilient Silicate Mineral
Zircon is a zirconium silicate mineral with the chemical formula ZrSiO₄. It is highly resistant to heat and chemical alteration, which is why it is found in ancient rocks and even in meteorites. Zircon crystals form in igneous rocks, particularly granites and pegmatites, and are also found in metamorphic and sedimentary rocks. During the formation of these rocks, zircon crystals can incorporate trace elements that influence their color.
The primary sources of gem-quality zircon include: - Cambodia: Known for producing high-quality blue and golden-yellow zircon. - Sri Lanka: A historic source for a variety of zircon colors, including brown, yellow, and green. - Thailand, Myanmar, and Australia: Also produce significant amounts of zircon, with Australia being a major source for brown and orange zircon. - Norway and the United States (New Mexico, California): Have smaller deposits.
Gemological Properties
The three December birthstones differ significantly in their physical and chemical properties, which affect their durability, care, and use in jewelry.
| Property | Turquoise | Tanzanite | Zircon |
|---|---|---|---|
| Chemical Formula | CuAl₆(PO₄)₄(OH)₈·4H₂O | Ca₂Al₃(SiO₄)₃(OH) | ZrSiO₄ |
| Crystal System | Triclinic | Orthorhombic | Tetragonal |
| Hardness (Mohs) | 5 – 6 | 6 – 7 | 6.5 – 7.5 |
| Specific Gravity | 2.60 – 2.90 | 3.35 | 4.6 – 4.7 |
| Refractive Index | 1.610 – 1.650 | 1.690 – 1.700 | 1.92 – 1.98 |
| Key Characteristics | Porous, often contains matrix, can be dyed or stabilized. | Strong trichroism (blue, violet, red-brown), heat-treated. | High refractive index and dispersion, can be heat-treated for color. |
Turquoise is relatively soft and porous, making it susceptible to damage from chemicals, heat, and pressure. Most commercial turquoise is stabilized (impregnated with a clear resin) to enhance durability and color. Its hardness can vary depending on its porosity and the amount of matrix.
Tanzanite has a moderate hardness, suitable for jewelry but requiring care to avoid scratches and blows. Its most notable optical property is trichroism—the ability to display three different colors (blue, violet, and red-brown) when viewed from different crystallographic directions. Most tanzanite on the market is heat-treated to achieve its desirable blue-to-violet hues.
Zircon is the hardest of the three, with a hardness approaching that of ruby and sapphire. It has a very high refractive index, giving it exceptional brilliance and fire, rivaling that of diamond. However, zircon is brittle and can be prone to chipping, so it is often cut in protective styles for jewelry. Colorless zircon is particularly valued for its diamond-like appearance.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, all three stones are imbued with symbolic meaning and metaphysical beliefs, though these are not scientifically verified.
- Turquoise is universally regarded as a stone of protection, wisdom, and tranquility. It is believed to promote emotional balance, calm the mind, and shield the wearer from negative energy. In many cultures, it is considered a conduit to the spiritual world and a symbol of immortality.
- Tanzanite is often called the "stone of transformation." It is associated with spiritual awakening, intuition, and the opening of the chakras (energy centers in the body). Its intense color is said to stimulate the throat and third-eye chakras, enhancing communication and psychic abilities.
- Zircon is believed to promote honor, purity, and wisdom. It is thought to help with self-realization and to bring prosperity and success. Colorless zircon, in particular, is associated with clarity of thought and purpose.
It is important to note that these metaphysical beliefs are part of cultural and spiritual traditions and are not supported by gemological science.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of these birthstones.
Turquoise: Due to its porosity and softness, turquoise requires gentle handling. * Cleaning: Use only warm water, a soft cloth, and mild soap. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals (including lotions, perfumes, and cosmetics), which can damage the stone and its stabilizing treatment. * Storage: Store separately from harder gemstones to prevent scratching. Keep it away from excessive heat or dry conditions, which can cause cracking.
Tanzanite: With a hardness of 6-7, tanzanite is relatively durable but can be brittle. * Cleaning: Warm, soapy water and a soft brush are safe. Avoid ultrasonic cleaners and steam, as sudden temperature changes can cause fractures. Always remove jewelry before physical activities. * Storage: Store in a soft cloth or padded box, away from other jewelry to prevent scratches.
Zircon: Zircon is the hardest of the three but is brittle. * Cleaning: Warm, soapy water and a soft brush are recommended. Avoid ultrasonic cleaners and sudden temperature changes, which can cause fractures, especially in heated stones. Do not expose zircon to rapid cooling. * Storage: Due to its brittleness, store zircon jewelry separately in a padded compartment to prevent chipping.
Conclusion
The December birthstones—turquoise, tanzanite, and zircon—offer a remarkable diversity of color, history, and meaning. Turquoise carries the weight of ancient civilizations and spiritual protection, tanzanite represents a modern geological wonder with its exclusive source and vibrant hue, and zircon provides timeless brilliance and durability. For the December-born, this trio provides a spectrum of choices, from the traditional sky-blue of turquoise to the fiery sparkle of zircon and the captivating violet of tanzanite. Understanding their origins, properties, and care ensures that these gemstones can be cherished for generations, serving as both beautiful adornments and meaningful personal symbols.