The final month of the year is uniquely distinguished in the world of gemology, offering not one, but three official birthstones: turquoise, tanzanite, and zircon. This rare triplet provides a remarkable spectrum of color, from the sky-blue of ancient lore to a deep, velvety violet and a brilliant, fiery sparkle. For those born in December, the choice is not merely aesthetic but a connection to a rich tapestry of geological history, cultural significance, and modern gemological innovation. This article delves into the unique characteristics, origins, and properties of these three captivating stones, providing a comprehensive guide for enthusiasts, collectors, and anyone seeking to understand the December birthstone legacy.
The selection of these stones reflects the evolution of birthstone lists, which have been periodically updated to include newly discovered or popularized gems. While turquoise has been a December birthstone for centuries, tanzanite and zircon were added in more recent times to provide contemporary and traditional options. Together, they represent a fascinating convergence of the ancient and the modern, offering a wide range of styles and price points. Understanding each stone's individual journey—from its formation deep within the Earth to its placement in a jewelry setting—enriches the appreciation of these December treasures.
Historical Significance and Cultural Lore
The history of December's birthstones is a story of ancient tradition meeting modern discovery. Turquoise is arguably the oldest of the trio, with a documented history spanning millennia. Revered by numerous civilizations, it has been a symbol of protection, wisdom, and good fortune. Its name itself derives from the French pierre turquoise, meaning "Turkish stone," reflecting its historic trade routes from Persia (modern-day Iran) through Turkey to Europe. Ancient Egyptian pharaohs and Chinese artisans alike prized the stone, often burying it with the dead as a protective talisman for the afterlife. For the December-born, turquoise carries this weight of ancient legacy, offering a connection to human history that is both profound and tangible.
In contrast, tanzanite is a product of the modern gemological age. Discovered in the 20th century, its history is remarkably short yet intensely vibrant. First identified in the Merelani Hills of Tanzania in 1967, it was initially mistaken for sapphire due to its striking blue-violet color. Recognizing its uniqueness, the jewelry industry, led by Tiffany & Co., launched a major marketing campaign in 1968, naming it after its country of origin. Its rapid rise to prominence led to its inclusion as an official December birthstone in 2002 by the American Gem Trade Association (AGTA), providing a modern, exclusive alternative for those born in the final month. Its lore is not of ancient tombs but of a single, geographically limited source, making it a truly 20th-century gem.
Zircon, the third December stone, holds a dual identity. It is one of the oldest minerals on Earth, with crystals found in Australian geology dating back over 4.4 billion years, making it a key tool for dating our planet's crust. However, its history as a gem is often overshadowed by a common misconception: it is frequently confused with the synthetic cubic zirconia (CZ), a completely different material. True zircon has been used in jewelry for centuries and was a popular diamond simulant in the Victorian era due to its high refractive index and brilliance. Its inclusion as a December birthstone provides a classic, traditional option, often in a fiery blue or colorless variety, that carries both ancient geological weight and a misunderstood gemological legacy.
Geological Formation and Global Sources
The origins of these three stones are as diverse as their colors, spanning different geological processes and continents.
Turquoise is a secondary mineral, meaning it forms near the Earth's surface through the interaction of existing minerals. It is a hydrated phosphate of copper and aluminum, typically found in arid regions where acidic, copper-rich water percolates through aluminum-bearing rocks. The most famous and historically significant source is the Nishapur region of Iran, which has produced the prized "robin's egg blue" turquoise for over 1,000 years. Other notable sources include the southwestern United States (Arizona, New Mexico, Nevada), Egypt, and China. The quality of turquoise is heavily influenced by its host rock, with "matrix" turquoise containing veins of the host material (like spiderweb patterns) being a valued characteristic in many cultures.
Tanzanite has an extraordinarily restricted geological origin. It is found in only one location on Earth: the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. The gem is a variety of the mineral zoisite, and its formation is linked to a unique geological event. The tectonic movement that formed the East African Rift Valley subjected existing zoisite rocks to intense heat and pressure, causing the trace element vanadium to impart the stone's signature blue-violet hue. This specific combination of geological conditions has not been replicated elsewhere, making tanzanite a truly singular gemstone. The mining area is divided into four blocks, with Block C being the most productive. This limited source contributes to its rarity and value.
Zircon is a zirconium silicate (ZrSiO₄) that forms in igneous and metamorphic rocks. Its crystals can be found in a variety of geological settings, including granite, pegmatite, and certain types of sand deposits. Major commercial sources include Australia (particularly the Murray Basin in New South Wales, which produces the classic blue zircon), Cambodia, Sri Lanka, and Thailand. Unlike tanzanite, zircon has a global distribution, though high-quality gem material is less common. The blue color in zircon is often the result of heat treatment applied to brownish crystals, a standard and accepted practice in the gem trade.
Gemological Properties: A Scientific Profile
Understanding the physical and chemical properties of these stones is crucial for identification, valuation, and care. The following table summarizes key data for each December birthstone, based on established gemological standards.
| Property | Turquoise | Tanzanite | Zircon |
|---|---|---|---|
| Chemical Formula | CuAl₆(PO₄)₄(OH)₈·4H₂O | Ca₂Al₃(SiO₄)₃(OH) | ZrSiO₄ |
| Crystal System | Triclinic | Orthorhombic | Tetragonal |
| Hardness (Mohs Scale) | 5 - 6 | 6.5 - 7 | 6.5 - 7.5 |
| Refractive Index | 1.61 - 1.65 | 1.69 - 1.70 | 1.92 - 2.01 |
| Specific Gravity | 2.6 - 2.9 | 3.35 | 4.6 - 4.7 |
| Luster | Waxy to subvitreous | Vitreous (glass-like) | Adamantine (brilliant) |
| Color Range | Sky blue, blue-green, greenish-blue | Blue to violet, often with pleochroism | Colorless, blue, yellow, brown, green |
Turquoise is notable for its relatively low hardness (5-6 on the Mohs scale), making it softer and more porous than many other gemstones. This porosity allows it to absorb oils and chemicals, which can alter its color over time. Its chemical composition includes water, making it sensitive to heat and prolonged exposure to sunlight, which can cause fading or cracking. The refractive index is moderate, and its luster is typically waxy, especially when untreated.
Tanzanite is harder than turquoise, with a Mohs hardness of 6.5 to 7, making it suitable for jewelry with appropriate care. Its most distinctive gemological feature is its strong pleochroism—the property of displaying different colors when viewed from different crystal directions. A tanzanite crystal may show blue, violet, and reddish-brown hues depending on the orientation. This is why lapidaries (gem cutters) carefully orient the rough crystal to maximize the desirable blue-violet color in the finished gem. Its refractive index is in the moderate range, and its vitreous luster gives it a clean, bright appearance.
Zircon is the hardest and densest of the three, with a Mohs hardness of 6.5 to 7.5. Its most remarkable property is its exceptionally high refractive index (1.92 - 2.01), which is higher than that of diamond (2.42). This, combined with its high dispersion (the ability to split white light into spectral colors), gives cut zircon a brilliant, fiery sparkle that rivals diamond. However, zircon is also known for its brittleness due to its crystal structure; it can be prone to chipping if knocked hard, despite its hardness. It is also radioactive in some specimens (particularly brown zircon), which can cause a gradual breakdown of the crystal structure over geological time.
Symbolism and Metaphysical Beliefs
Across cultures, gemstones have been attributed with symbolic meanings and healing properties, a tradition that continues today.
Turquoise is universally associated with protection, tranquility, and good fortune. In many Native American cultures, it is considered a sacred stone, a piece of the sky fallen to Earth. It is believed to ward off negative energy, promote inner calm, and enhance communication. Persian warriors wore it for protection in battle, and it was thought to change color to warn the wearer of danger or illness. For the December-born, turquoise symbolizes a shield of positivity and a connection to wisdom and spiritual grounding.
Tanzanite, as a modern discovery, has quickly accumulated its own lore. It is often called the "stone of transformation" and is believed to facilitate a higher consciousness, intuition, and spiritual perception. Its striking color is linked to the throat and third-eye chakras, promoting clear communication and a deeper understanding of oneself. Some metaphysical practitioners associate tanzanite with the unique energy of its single source location, viewing it as a stone of uniqueness and purpose. Its symbolism is forward-looking, aligning with its 20th-century origin.
Zircon has a long-standing reputation as a stone of wisdom, honor, and purity. In the Middle Ages, it was believed to aid in sleep, promote prosperity, and ward off evil spirits. Colorless zircon, in particular, was valued for its diamond-like appearance and was thought to bring clarity of mind and purpose. Blue zircon is associated with peace and tranquility, while yellow zircon is linked to joy and creativity. Its ancient geological heritage lends it a symbolism of endurance and timelessness, making it a meaningful choice for those who value tradition and strength.
Care and Maintenance
Proper care is essential to preserve the beauty and integrity of these gemstones, with requirements varying significantly based on their individual properties.
Turquoise requires the most careful handling due to its softness and porosity. It should be protected from chemicals, including perfumes, lotions, and household cleaners, which can cause discoloration or surface damage. Cleaning should be done with a soft, dry cloth. Avoid ultrasonic cleaners and steam, as the vibrations and heat can cause cracking. It is best to store turquoise jewelry separately to prevent scratching by harder stones.
Tanzanite, while harder than turquoise, is still relatively brittle and can be sensitive to rapid temperature changes. It should not be exposed to extreme heat or sudden cooling. Cleaning is best done with warm, soapy water and a soft brush. Ultrasonic cleaners are generally not recommended, as the vibrations could potentially damage the stone, especially if it has inclusions or fractures. Steam cleaning should also be avoided.
Zircon, despite its hardness, is brittle and can be chipped by a sharp blow. It is also sensitive to heat, and high temperatures can alter its color or cause fracturing. Therefore, it should be kept away from high-heat environments and handled with care during setting and wear. Cleaning with warm, soapy water and a soft brush is safe. Ultrasonic cleaners are risky and should be avoided, as is steam cleaning. Proper storage in a padded jewelry box is advised to protect it from impact.
Conclusion
The December birthstones—turquoise, tanzanite, and zircon—offer a remarkable diversity that reflects the richness of the gem world itself. From the ancient, protective sky-blue of turquoise to the transformative, singular violet of tanzanite and the brilliant, timeless fire of zircon, each stone carries a unique story of geological formation, cultural significance, and scientific wonder. For those born in December, the choice between these three gems is not merely a matter of color preference but an opportunity to connect with a specific narrative—be it one of ancient legacy, modern discovery, or enduring strength. By understanding their properties, origins, and care requirements, one can fully appreciate the enduring beauty and symbolic depth that these vibrant stones bring to the world of jewelry and personal adornment.