The month of December is traditionally associated with a trio of gemstones, each offering a distinct palette of color and character: the ancient sky-blue turquoise, the fiery brilliance of zircon, and the captivating blue-violet of tanzanite. These stones are collectively recognized as the birthstones for December, symbolizing good fortune, success, and a connection to the season's celestial events. While turquoise holds the longest historical claim as December’s traditional stone, zircon and tanzanite have been embraced as modern additions, providing a diverse range of options for those born in the final month of the year. This article explores the history, geological origins, gemological properties, and cultural significance of these three remarkable gems, drawing exclusively from authoritative sources to provide a comprehensive guide for gemstone enthusiasts and collectors.
History and Lore: From Ancient Symbolism to Modern Birthstones
The concept of birthstones has deep roots in historical tradition, though the specific assignment of gems to months has evolved over centuries. The practice is often traced back to the Breastplate of Aaron, a ceremonial garment described in the Old Testament, which was adorned with twelve gemstones representing the twelve tribes of Israel. These stones were later associated with the twelve signs of the zodiac and, eventually, the twelve months of the year. The modern list of birthstones, largely standardized in 1912 by the American National Association of Jewelers, solidified the gemstones we recognize today.
For December, the traditional and most ancient birthstone is turquoise. Historical records indicate that turquoise has been prized for millennia. Its name is derived from the French pierre turquoise, meaning "Turkish stone," as the gem was initially transported to Europe through Turkey from mines in the Persian Empire (modern-day Iran). Ancient cultures, including the Egyptians, Persians, and Native Americans, revered turquoise for its protective qualities and vibrant color. It was often used in amulets, jewelry, and ceremonial objects. The sources note that turquoise is "considered a symbol of good fortune and success," a belief that has persisted through various cultures and eras.
Zircon is another of December’s traditional birthstones, with a history that is both geological and mythological. It is one of the oldest minerals on Earth, with some zircon crystals dating back over 4 billion years. For centuries, clear zircon was mistaken for diamond due to its high refractive index and brilliance, earning it the historical name "jacinth." In the 19th century, before the widespread use of synthetic alternatives, blue zircon was particularly popular in Victorian-era jewelry. While its association with December is well-established in modern birthstone lists, its historical lore is often intertwined with that of diamond and other high-index gems.
The most recent addition to the December birthstone family is tanzanite. This gemstone was not discovered until the mid-20th century, making its history remarkably brief compared to turquoise and zircon. Its debut on the gemological scene was dramatic, and its rapid rise to prominence led to its official recognition as a December birthstone in 2002 by the American Gem Trade Association (AGTA), expanding the traditional list. The sources confirm that zircon and tanzanite are now considered December birthstones alongside turquoise, offering a modern triad of choices.
Geological Formation and Sources
The three December birthstones originate from vastly different geological processes and are mined in distinct regions of the world.
Turquoise is a secondary mineral that forms in arid or semi-arid regions where acidic, copper-rich groundwater percolates through rocks containing aluminum and phosphorus. Over geological time, this interaction creates nodules or veins of turquoise within host rock, often quartz or limonite. The most historically significant sources are in the Persian Empire (modern-day Iran), which produced the prized "robin's egg blue" turquoise. Other notable sources include the Southwestern United States (Arizona, New Mexico, Nevada), China, and Egypt. The quality of turquoise is heavily influenced by its matrix—the host rock in which it is found—and its color, which ranges from sky blue to greenish-blue.
Zircon is a zirconium silicate (ZrSiO₄) that crystallizes in igneous and metamorphic rocks. It is a common accessory mineral in granite and granitic pegmatites. Significant gem-quality zircon deposits are found in Sri Lanka, Cambodia, Thailand, and Australia. Australian zircon, often found in sedimentary deposits, is known for its high-quality crystals. Zircon can also be found in metamorphic rocks and alluvial (river) deposits, where it is often mined by placer methods. Its durability and resistance to weathering allow it to survive in secondary deposits, making it accessible for mining.
Tanzanite is the trade name for the blue to violet-blue variety of the mineral zoisite. It is found exclusively in a small, four-square-kilometer area in the Merelani Hills of Northern Tanzania, near the base of Mount Kilimanjaro. This geographic limitation makes tanzanite one of the rarest gemstones on Earth. The gem forms through a complex geological process involving the metamorphism of calc-silicate rocks and the introduction of vanadium, which is responsible for its distinctive color. The discovery of tanzanite in 1967 by a local Masai herdsman, followed by its promotion by Tiffany & Co., transformed it from an unknown mineral into a globally recognized gemstone.
Gemological Properties
Understanding the physical and optical properties of these gemstones is essential for identification, valuation, and care. The following table summarizes key gemological data for turquoise, zircon, and tanzanite, based on established gemological standards reflected in the provided sources.
| Gemstone | Chemical Formula | Crystal System | Mohs Hardness | Refractive Index | Typical Colors | Notable Treatments |
|---|---|---|---|---|---|---|
| Turquoise | CuAl₆(PO₄)₄(OH)₈·4H₂O | Triclinic | 5 - 6 | 1.61 - 1.65 | Sky blue to greenish-blue | Stabilization (waxing, resin impregnation), dyeing |
| Zircon | ZrSiO₄ | Tetragonal | 6.5 - 7.5 | 1.92 - 2.01 (High) | Colorless, blue, yellow, brown, red (hyacinth) | Heat treatment (common for color improvement) |
| Tanzanite (Zoisite) | Ca₂Al₃(SiO₄)₃(OH) | Orthorhombic | 6.5 - 7 | 1.69 - 1.70 | Blue to violet-blue | Heat treatment (to enhance blue color) |
Turquoise is relatively soft compared to many gemstones, with a hardness of 5 to 6 on the Mohs scale. This makes it susceptible to scratching and requires careful handling. Its chemical composition includes water, and it is porous, which is why many commercial turquoise stones are stabilized—impregnated with wax or resin—to improve durability and color consistency. The color of turquoise is primarily due to copper, with iron contributing to greenish hues. The presence of the host rock matrix can also affect its appearance and value.
Zircon is a significantly harder and more durable gemstone, with a Mohs hardness of 6.5 to 7.5. Its most remarkable property is its high refractive index (1.92-2.01), which gives it exceptional brilliance and fire, surpassing that of diamond in some cases. Zircon is pleochroic, meaning it can display different colors when viewed from different crystal directions; for example, brownish zircon may show blue and green hues. It is also sensitive to heat and can crack during cutting or heating if not handled carefully. Most blue zircon on the market is heat-treated from brown or greenish crystals.
Tanzanite has a hardness of 6.5 to 7, making it suitable for jewelry but requiring some care to avoid scratches. Its most distinctive feature is its strong trichroism, displaying three different colors: blue, violet, and burgundy/red, depending on the crystal orientation. Almost all tanzanite is heat-treated to achieve its vivid blue-violet color; the natural brownish-yellow zoisite is not commercially viable without this treatment. The heat treatment is stable and permanent, and it is an accepted industry practice.
Symbolism and Metaphysical Beliefs
Throughout history, gemstones have been imbued with symbolic meanings and metaphysical properties. While modern gemology focuses on physical characteristics, these cultural beliefs add a layer of significance to the stones.
Turquoise has been universally associated with protection, good fortune, and healing. Ancient Persian warriors wore turquoise amulets for protection in battle, and it was believed to ward off evil and bring peace. In Native American cultures, turquoise is sacred, representing the sky, water, and the earth's connection to the heavens. It is often called the "sky stone" and is thought to promote wisdom, tranquility, and balance. The sources explicitly state that turquoise is "considered a symbol of good fortune and success," aligning with its long-standing lore.
Zircon has a more varied history of symbolism. In the Middle Ages, it was believed to promote rest, ward off evil spirits, and bring prosperity. Clear zircon was used as a protective stone for travelers. Its brilliant fire has also linked it to enlightenment and spiritual clarity. While not as heavily documented in the sources as turquoise, zircon's historical use in jewelry and its diamond-like appearance have contributed to its association with purity and strength.
Tanzanite, being a modern gemstone, lacks the ancient lore of turquoise and zircon. However, it has quickly accumulated its own symbolism. Often called the "stone of transformation," tanzanite is associated with spiritual awakening, intuition, and higher consciousness. Its discovery at the foot of Mount Kilimanjaro, a site of great spiritual significance, adds to its mystique. In the short time it has been known, tanzanite has become a symbol of unique individuality and modern elegance.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone jewelry. The differing physical properties of turquoise, zircon, and tanzanite necessitate specific handling guidelines.
Turquoise is the most delicate of the three due to its lower hardness and porosity. It should be protected from chemicals, cosmetics, and prolonged exposure to water, which can cause discoloration or damage the stabilizing materials. Cleaning should be done with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals. It is best to remove turquoise jewelry before engaging in physical activities or household chores to prevent scratches and impacts.
Zircon is relatively durable but can be brittle due to its crystal structure. While it is hard enough to resist scratching from everyday wear, it can fracture if struck with sufficient force. It is generally safe to clean with warm soapy water and a soft brush. However, caution is needed with ultrasonic cleaners, as the vibrations may cause existing fractures to worsen. Zircon is also sensitive to heat, so it should be kept away from high temperatures.
Tanzanite, with a hardness of 6.5 to 7, is moderately durable but should be handled with care. It is prone to chipping and scratching if subjected to rough wear. Like zircon, it is best cleaned with warm soapy water and a soft brush. Ultrasonic cleaners and steam cleaning are not recommended, as the heat and vibrations can damage the stone, especially if it has been treated or has inclusions. It is advisable to store tanzanite jewelry separately from other gems to prevent scratches.
Conclusion
The December birthstones—turquoise, zircon, and tanzanite—offer a remarkable diversity in color, history, and character. Turquoise stands as the ancient guardian of the trio, its sky-blue hue a timeless symbol of protection and good fortune. Zircon, with its brilliant fire and ancient geological origins, provides a durable and sparkling alternative. Tanzanite, the newest member, captivates with its unique blue-violet trichroism and represents a modern addition to the birthstone tradition. Together, they reflect the multifaceted nature of December itself, a month of celebration, reflection, and the promise of new beginnings. For those born in December, this trio of gemstones provides a wealth of choices, each carrying its own story and significance, from the depths of ancient earth to the vibrant markets of the modern world.