The month of December is uniquely associated with three distinct birthstones: turquoise, zircon, and tanzanite. This trio represents a spectrum of color, from the serene sky-blue of turquoise to the fiery brilliance of zircon and the vivid violet-blue of tanzanite. Unlike months with a single traditional stone, December's birthstones offer a diverse palette, each with its own geological story and cultural significance. As symbols of good fortune, success, and clarity, these gems are deeply intertwined with the winter season, from the ancient festivals of light to the modern celebrations of the year's end. This article explores the history, properties, sources, and lore of these three remarkable gems, providing a comprehensive guide for enthusiasts, collectors, and anyone born in the final month of the year.
History and Lore: From Ancient Traditions to Modern Designations
The tradition of assigning specific stones to birth months has evolved over centuries, with December's selection being particularly fluid. Historical sources indicate that turquoise is the traditional birthstone for December. It has long been considered a symbol of good fortune and success, a belief that has persisted across various cultures. The connection between gemstones and specific months is often rooted in ancient texts and clerical traditions, which sought to align the twelve stones of the High Priest's breastplate with the twelve months of the year. While the modern list of birthstones was standardized in 1912 by the American National Association of Jewelers, the historical and cultural associations of these stones run much deeper.
The month of December itself is rich in historical and astronomical significance. In ancient Roman times, the calendar initially had only ten months, beginning with March, and the winter period was not assigned its own months. The month of December, originally consisting of 30 days, was later shortened and then expanded again in the Julian calendar to its current 31 days. This period has long been associated with festivals of light and the rebirth of the sun. The Winter Solstice, occurring around December 21, was celebrated through traditions like Yule, marking the turning point when the sun begins its return. St. Lucia’s Day, on December 13, is also linked to light, as her feast day once occurred on the shortest day of the year. These cultural contexts of light and renewal provide a fitting backdrop for the vibrant hues of December's birthstones.
While turquoise holds the title of the traditional stone, the modern birthstone list has expanded to include zircon and tanzanite. This evolution reflects the jewelry industry's desire to offer more variety and color choices to consumers. Zircon, one of the oldest minerals on Earth, has been used in jewelry for centuries, though it is often confused with the synthetic cubic zirconia. Tanzanite, a relative newcomer, was only discovered in the 20th century and quickly gained popularity for its unique color. The inclusion of these three stones provides a modern, versatile selection for December-born individuals, each stone carrying its own distinct geological and aesthetic narrative.
Geological Formation and Sources
Understanding the origins of these gems requires a look at their unique geological formation processes. Each of the three December stones forms under vastly different conditions, leading to their diverse properties and global sources.
Turquoise is a secondary mineral, meaning it forms in the near-surface environment where pre-existing minerals are altered by water and other elements. It is a hydrated phosphate of copper and aluminum. The most prized turquoise often comes from arid regions where water percolates through copper-rich rocks. Historically, significant sources include the ancient mines of Persia (modern-day Iran), which have produced the renowned "Persian blue" turquoise for millennia. In the United States, the Southwest, particularly Nevada and Arizona, is famous for its turquoise deposits, which have been mined by Native American cultures for centuries. The specific conditions of formation, including the presence of iron or other impurities, can affect the stone's color, ranging from sky blue to greenish-blue.
Zircon is a zirconium silicate (ZrSiO₄) and is one of the oldest minerals on Earth, with crystals found in ancient rocks that are billions of years old. It forms in igneous and metamorphic rocks. The gem-quality zircon used in jewelry is typically found in alluvial deposits, where it has been weathered from its host rock and concentrated in riverbeds and coastal areas. Major sources include Cambodia, Sri Lanka, and Australia. Australian zircon, often found in placer deposits, is a significant source of the gem. The stone's durability and resistance to weathering allow it to survive transport and accumulate in these secondary deposits, making it a durable gemstone for jewelry.
Tanzanite is a variety of the mineral zoisite, specifically the blue to violet-blue variety colored by vanadium. It is a relatively young discovery in the gemological world. Tanzanite is found exclusively in a single, small mining area in the Merelani Hills of Northern Tanzania, near the base of Mount Kilimanjaro. This geographic exclusivity is a key part of its allure. The formation of tanzanite is linked to a unique geological event: the metamorphism of a zoisite-rich rock. The process involves the alteration of the original mineral by heat and pressure, which, in the presence of vanadium, produces the signature blue color. Due to its limited geographic occurrence, tanzanite is considered a "one-generation" gemstone, with current mining operations depleting the known reserves.
Gemological Properties
The scientific characteristics of these stones define their beauty, durability, and care requirements. While all three are used in jewelry, their physical and optical properties differ significantly.
Turquoise is valued for its distinctive color and opaque to translucent nature. It has a hardness of 5 to 6 on the Mohs scale, making it relatively soft and susceptible to scratching and abrasion. This lower hardness necessitates careful handling and protective settings in jewelry. Its specific gravity ranges from 2.6 to 2.9, and it has a refractive index of about 1.61 to 1.65. Turquoise is often treated or stabilized with resins or waxes to enhance its color and durability, a common practice in the trade. The presence of a matrix, or host rock, within the stone is common and can affect its value and appearance.
Zircon is one of the hardest and densest of the December stones. It has a hardness of 7.5 on the Mohs scale, making it durable enough for everyday wear in rings and other jewelry. Its high refractive index (1.92 to 2.01) and strong dispersion (0.039) give it exceptional brilliance and fire, often compared to that of diamond. Zircon is a birefringent mineral, meaning it can show double refraction, which can sometimes be visible to the naked eye in larger stones. It is available in a range of colors, including blue, yellow, green, and red, with blue zircon being the most popular for December. The stone is also known for its high specific gravity, typically between 4.6 and 4.7.
Tanzanite is known for its trichroism, a property where the stone displays three different colors—typically blue, violet, and red—when viewed from different crystal directions. This characteristic is a key identifier and adds to its visual interest. Tanzanite has a hardness of 6.5 to 7 on the Mohs scale, making it suitable for most jewelry types, though it requires protection from sharp blows. It has a refractive index of 1.69 to 1.70 and a specific gravity of 3.35. The most prized color is a rich, saturated violet-blue, often referred to as "cornflower blue." Heat treatment is standard for tanzanite to remove brownish hues and develop its signature blue color.
The following table summarizes the key gemological properties of the three December birthstones based on the available information:
| Property | Turquoise | Zircon | Tanzanite |
|---|---|---|---|
| Chemical Formula | Hydrated phosphate of copper and aluminum | Zirconium silicate (ZrSiO₄) | Calcium aluminum silicate (Ca₂Al₃(SiO₄)₃(OH)) colored by vanadium |
| Mohs Hardness | 5 - 6 | 7.5 | 6.5 - 7 |
| Refractive Index | 1.61 - 1.65 | 1.92 - 2.01 | 1.69 - 1.70 |
| Specific Gravity | 2.6 - 2.9 | 4.6 - 4.7 | 3.35 |
| Key Optical Feature | Opaque to translucent, often with matrix | High brilliance and fire (dispersion) | Trichroism (blue, violet, red) |
| Common Treatments | Stabilization with resins/waxes | Heat treatment to enhance color | Heat treatment to remove brown hues |
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, these stones are imbued with rich symbolism and metaphysical properties that have been cherished for generations.
Turquoise is universally regarded as a stone of protection, good fortune, and success. Its traditional status as a symbol of good fortune is well-documented. Across various cultures, it has been worn as an amulet to ward off evil and bring luck to the wearer. The stone's connection to the sky and water in its color reinforces its symbolic role as a bridge between the earth and the heavens. In many traditions, turquoise is believed to promote healing, balance, and emotional stability, making it a popular stone for spiritual and wellness practices.
Zircon, while less frequently discussed in metaphysical contexts in the provided sources, is historically associated with wisdom, honor, and purity. Its durability and brilliant fire have led to its use in crowns and royal jewelry, symbolizing power and clarity. In some traditions, it is believed to aid in sleep and promote prosperity. The stone's ancient origins contribute to its aura of timelessness and stability.
Tanzanite, as a modern discovery, has quickly developed its own set of symbolic meanings. It is often associated with transformation, spiritual awakening, and enhanced intuition. Its unique trichroism is seen as a metaphor for seeing multiple perspectives or unlocking hidden truths. The stone's exclusive origin in Tanzania lends it an air of rarity and specialness, making it a symbol of individuality and unique destiny for those born in December.
The symbolism of these stones is often intertwined with the month of December's themes of light, renewal, and celebration. As the world turns toward the return of the sun and the end of the year, the vibrant colors of turquoise, zircon, and tanzanite serve as tangible reminders of hope, clarity, and the promise of new beginnings.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone, and the December birthstones each have specific requirements due to their distinct physical properties.
Turquoise, with its moderate hardness of 5 to 6, is the most delicate of the trio. It is susceptible to scratches, chemicals, and prolonged exposure to heat or direct sunlight, which can cause fading or discoloration. To clean turquoise, use only a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals, including household cleaners and cosmetics. It is best to store turquoise jewelry separately in a soft pouch to prevent scratching. Periodic professional cleaning and re-polishing may be necessary to maintain its luster.
Zircon, despite its hardness, can be brittle due to its crystal structure. It is prone to chipping if struck with significant force. Cleaning zircon is relatively straightforward; it can be washed with warm water, mild soap, and a soft brush. However, it is advisable to avoid ultrasonic cleaners, as vibrations can exacerbate any existing fractures. The stone is generally stable, but some blue zircon may fade with prolonged exposure to strong light or heat, so storing it away from direct sunlight is recommended.
Tanzanite has a hardness of 6.5 to 7, making it durable enough for most jewelry. However, it has perfect cleavage in one direction, meaning it can split if struck with a sharp blow along that plane. Care should be taken to protect tanzanite rings from hard impacts. Cleaning can be done with warm, soapy water and a soft brush. As with zircon, ultrasonic cleaners are not recommended due to the risk of shock. Heat treatment is a standard practice for tanzanite, but further exposure to high heat should be avoided, as it can alter the stone's color.
For all three stones, the best practice is regular, gentle cleaning and careful storage. When in doubt, consulting a professional jeweler is the safest course of action, especially for valuable or heirloom pieces.
Conclusion
The birthstones of December—turquoise, zircon, and tanzanite—offer a remarkable diversity of color, history, and geological origin. From the ancient, protective symbolism of turquoise to the brilliant fire of zircon and the transformative energy of tanzanite, each stone provides a unique connection to the month's themes of light, renewal, and celebration. Their varied properties require specific care, but when properly maintained, they can be cherished for generations. Whether chosen for their traditional significance, their stunning beauty, or their personal resonance, these three gems capture the essence of December, making them enduring symbols for anyone born in the year's final month.