The final month of the year is uniquely distinguished by not one, but three official birthstones: Turquoise, Zircon, and Tanzanite. This trio offers an extraordinary spectrum of color, history, and geological origin, providing those born in December with a remarkable range of choices. While Turquoise stands as one of the oldest known gemstones in human history, Zircon is the oldest mineral on Earth, and the vibrant Tanzanite is a celebrated modern discovery. Together, they represent a fascinating journey through time, from ancient deserts and primordial crusts to the contemporary mines of East Africa. This article provides a detailed exploration of these three captivating gemstones, delving into their unique gemological properties, storied pasts, and the symbolic meanings that have made them enduringly popular.
History and Lore
The historical narratives of the December birthstones are as varied as their appearances. Each stone carries a legacy steeped in ancient beliefs, trade, and cultural significance.
Turquoise: The Ancient Talisman
Turquoise boasts a history that stretches back millennia, making it one of the world's most ancient gem materials. Evidence of its use has been found in ancient Egyptian tombs, where it was fashioned into intricate jewelry and placed on mummies to ensure safe passage to the afterlife. The stone’s name itself is derived from the French phrase pierre turquoise, meaning "Turkish stone," reflecting its introduction to Europe from Persian mines via Turkish traders. For centuries, it has been revered across continents, from the protective amulets of Persian warriors to the ornate silver-and-turquoise jewelry of the Indigenous peoples of the American Southwest. Its sky-blue and green hues were universally associated with water, the heavens, and protection from harm.
Zircon: The Stone of Royalty and Protection
Zircon is the oldest mineral on Earth, with some specimens dating back over 4.4 billion years. Its use as a gemstone is also ancient; during the Middle Ages, it was believed to promote honor, prosperity, and wisdom in its wearer. Green zircon was once considered the most valuable variety, but today, the colorless and golden-brown stones are most commonly encountered. For much of its history, zircon was confused with diamond due to its high brilliance and fire. It was often used as a less expensive diamond substitute, a practice that led to the modern term "Matura diamond" for high-quality colorless zircon. This historical confusion, however, belies its own intrinsic beauty and ancient lineage.
Tanzanite: The Gem of a Generation
In stark contrast to its ancient counterparts, Tanzanite is a thoroughly modern gemstone. It was not recognized by the gemological world until 1967. Its discovery is attributed to a Masai tribesman, Ali Juuyawatu, who found transparent blue crystals of a previously unknown mineral near Mount Kilimanjaro in Tanzania. Initially, the stones were sold as blue zircon until their true identity was confirmed. The gem was later named "Tanzanite" by Tiffany & Co., which recognized its potential and launched a major marketing campaign in 1968, promoting it as "the most beautiful blue gemstone discovered in 2,000 years." Its origin from a single, small mining area in the Merelani Hills of Tanzania makes it geologically exclusive and has fueled its reputation as a rare and precious treasure.
Geological Formation and Sources
The origins of these stones are as diverse as their histories, spanning different geological processes and continents.
Turquoise: A Hydrated Copper Mineral
Turquoise is not a single mineral but a hydrated phosphate of copper and aluminum. It forms in arid regions where acidic, copper-rich groundwater seeps through rock, reacting with minerals containing aluminum and phosphorus. This slow process, occurring over millions of years, creates the nodules and veins of turquoise that are mined. The most significant sources of turquoise are found in Iran (historically the source of the finest "Persian turquoise") and the Southwestern United States (Arizona, New Mexico, and Nevada). Other notable sources include China, Egypt, and Mexico. The color of turquoise is directly tied to its copper content; higher copper levels produce a vibrant blue, while iron and chromium can lead to greenish hues.
Zircon: A Primary Zirconium Silicate
Zircon (ZrSiO₄) is a primary mineral, meaning it crystallizes directly from magma. It is found in igneous and metamorphic rocks and is highly resistant to weathering, which is why it is often found in alluvial deposits (riverbeds and coastal sands). Its durability allows it to survive through geological ages. Major sources of gem-quality zircon include Cambodia, Sri Lanka, and Thailand, which are known for producing high-quality brownish and golden zircon. Australia is also a significant source, particularly for brown zircon. The colorless and blue varieties often seen in jewelry are typically the result of heat treatment of brown zircon crystals.
Tanzanite: A Unique Geological Anomaly
Tanzanite’s formation is a geological rarity. It is a variety of the mineral zoisite and gets its blue color from trace amounts of vanadium. The conditions required for its formation are so specific that the only known commercial source is a small, four-square-kilometer mining area in the Merelani Hills of northern Tanzania, near the foothills of Mount Kilimanjaro. This extreme geographic limitation makes tanzanite at least a thousand times rarer than diamond. The stones are typically found in elongated, tabular crystals. Due to the scarcity and finite nature of the deposit, tanzanite is often considered a "generation stone," destined to be mined out within a few decades.
Gemological Properties
Understanding the physical and chemical characteristics of these gemstones is crucial for both appreciation and practical use. The following table summarizes their key properties.
| Property | Turquoise | Zircon | Tanzanite (Zoisite) |
|---|---|---|---|
| Chemical Composition | Hydrated copper aluminum phosphate (CuAl₆(PO₄)₄(OH)₈·4H₂O) | Zirconium silicate (ZrSiO₄) | Calcium aluminum hydroxyl silicate with vanadium (Ca₂Al₃(SiO₄)₃(OH)) |
| Hardness (Mohs Scale) | 5 - 6 | 6.5 - 7.5 | 6.5 - 7 |
| Crystal System | Triclinic | Tetragonal | Orthorhombic |
| Refractive Index | 1.610 - 1.650 | 1.925 - 2.015 | 1.691 - 1.700 |
| Luster | Waxy to subvitreous | Adamantine (brilliant) | Vitreous (glass-like) |
| Common Treatments | Stabilization, dyeing, waxing | Heat treatment (for color) | Heat treatment (standard) |
Turquoise: A Porous and Variable Gem
With a hardness of 5 to 6 on the Mohs scale, turquoise is relatively soft compared to other gemstones. It is also porous and can be susceptible to chemicals, heat, and even pressure. These characteristics mean that much of the turquoise on the market has been treated to enhance its durability and color. "Stabilized turquoise" has been impregnated with a clear resin to increase its hardness and prevent discoloration from skin oils. While some purists prefer natural, untreated stone, stabilization makes turquoise much more practical for use in jewelry, especially rings. The color can range from sky blue to apple green, often with a distinctive matrix (a web-like pattern of the host rock).
Zircon: Exceptional Brilliance and Fire
Zircon is one of the most brilliant of all natural gemstones, possessing a high refractive index that rivals that of diamond. Its "fire" (dispersion) is also superior to diamond's, meaning it can display rainbow flashes of color more intensely. However, zircon has a perfect cleavage in two directions, making it somewhat brittle and susceptible to chipping if struck hard. This property requires careful handling during cutting and setting. The most valued colors are the fiery red (hyacinth), brilliant blue, and colorless varieties. Most blue zircon is the result of heat treatment, which transforms common brown zircon into a vibrant blue.
Tanzanite: The Trichroic Treasure
Tanzanite is celebrated for its strong pleochroism—the ability to show different colors when viewed from different crystal directions. It is typically trichroic, displaying blue, violet, and burgundy-red tones simultaneously. In its rough state, it often appears as a brownish crystal. The signature blue-to-violet color that tanzanite is famous for is almost always the result of a controlled heat treatment process, which removes the brownish hues and enhances the blue and violet. This treatment is stable and is considered a standard industry practice. With a hardness of 6.5 to 7, it is durable enough for most jewelry applications but requires care to avoid chipping due to its cleavage properties.
Symbolism and Metaphysical Beliefs
Across cultures and centuries, the December birthstones have been imbued with powerful symbolic meanings and metaphysical properties.
Turquoise has long been regarded as a stone of protection, wisdom, and good fortune. It was believed to break when it had protected its wearer from danger or illness. Many Native American cultures consider it a sacred stone, representing the sky and water, and it is often used in ceremonies and as a conduit for connecting with the spiritual world. It is also associated with tranquility, peace, and emotional balance.
Zircon is said to bring honor, wisdom, and prosperity to its wearer. In the Middle Ages, it was believed to induce sound sleep, ward off evil spirits, and promote riches and honor. Blue zircon, in particular, is associated with clarity of thought and spiritual grounding. It is often considered a stone of virtue and purity.
As a modern discovery, Tanzanite has quickly developed its own lore. It is often called the "stone of transformation" and is believed to facilitate a higher consciousness, intuition, and spiritual perception. Its discovery near Mount Kilimanjaro lends it a sense of majestic energy. Tiffany & Co. marketed it as the "gem of a generation," and it is associated with new beginnings and a unique, once-in-a-lifetime perspective.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of these gemstones, and the approach varies significantly for each.
Caring for Turquoise
Due to its porosity and relative softness, turquoise requires gentle care. It is sensitive to chemicals, including cosmetics, perfumes, lotions, and even some soaps, which can cause discoloration. It should be the last thing you put on and the first thing you take off. Clean it only with warm water, a mild soap, and a soft cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals. Stabilized turquoise is more resistant but should still be treated with care.
Caring for Zircon
Zircon’s perfect cleavage makes it vulnerable to impact. It should be stored carefully, wrapped in soft cloth or kept in a separate compartment of a jewelry box to prevent scratching or chipping. While it is relatively hard, it is not as tough as some other gems. Cleaning can be done with warm, soapy water and a soft brush. Avoid sudden temperature changes, as extreme heat can alter the stone's color (especially in blue zircon), and thermal shock can cause fractures.
Caring for Tanzanite
Like zircon, tanzanite has cleavage, making it susceptible to chipping and fracture if struck. It is not recommended for rings that will be worn daily, such as engagement rings, but is excellent for pendants, earrings, and occasion rings. Clean tanzanite with warm, soapy water and a soft brush. Avoid ultrasonic cleaners and steam cleaners, as the vibrations and heat can cause the stone to fracture. Store it separately to protect it from harder gems.
Conclusion
The birthstones of December—Turquoise, Zircon, and Tanzanite—offer a compelling narrative of geological wonder, human history, and symbolic power. From the ancient, protective talisman of Turquoise and the primordial, brilliant fire of Zircon to the singular, vibrant beauty of Tanzanite, each gem provides a distinct identity for those born in the final month of the year. Their varied hardness, cleavage, and care requirements underscore the importance of understanding the unique nature of each stone. Whether chosen for its historical resonance, its rare geological origin, or its captivating color, a December birthstone is a timeless treasure, connecting its wearer to a rich and diverse legacy of beauty and meaning.