The month of December is uniquely associated with three distinct birthstones: turquoise, zircon, and tanzanite. This multiplicity offers individuals born in the final month of the year a diverse palette of colors, primarily centered on the spectrum of blue. Unlike months with a single designated gem, December’s trio provides a choice between ancient tradition, natural brilliance, and modern discovery. Each stone carries its own history, geological origin, and set of gemological properties, allowing for personal expression through jewelry that can range from earthy and opaque to fiery and transparent.
These three gems are mined across the globe, from the arid landscapes of the American Southwest to the alluvial deposits of Australia and the volcanic terrain of East Africa. Their selection as December’s birthstones is the result of an evolving historical process, where the traditional turquoise was joined by zircon and later by tanzanite to create a more comprehensive and colorful modern list. Understanding the distinctions between these three stones—their formation, their physical characteristics, and their cultural significance—provides a deeper appreciation for the choices available to those celebrating a December birthday.
History and Evolution of the December Birthstone
The concept of birthstones has ancient roots, tracing back to the breastplate of Aaron described in the Old Testament, which featured twelve stones representing the twelve tribes of Israel. Over centuries, these stones became associated with zodiac signs and, eventually, calendar months. The modern standardized list, however, is a relatively recent development in the United States.
The National Association of Jewelers (now Jewelers of America) established the first official birthstone chart in 1912. This initial list replaced many traditional, often opaque stones with clearer, more commercially desirable gems. Turquoise was included as the sole birthstone for December in this first modern chart. The list continued to evolve. In 1952, the American Gem Trade Association added tanzanite as a December birthstone, marking a significant update to the list after 50 years. Zircon was also officially recognized as a December option, though sources vary on the exact timeline of its addition, with some noting its inclusion in earlier lists.
The result is a contemporary chart that offers three blue-hued choices: the traditional turquoise, the fiery zircon, and the modern tanzanite. This evolution reflects both geological discoveries—such as the 1967 find of tanzanite in Tanzania—and market trends, providing consumers with a range of options in terms of color, durability, and price.
Turquoise: The Ancient Stone of the Southwest
Turquoise is arguably the most historically significant of the December birthstones, with a lineage stretching back millennia. As an opaque mineral, its appeal lies in its distinctive color, which ranges from sky blue to blue-green and yellowish green. The most prized color is a bright, even blue, a hue that has captivated human culture since antiquity.
Geological Formation and Sources
Turquoise is a hydrous phosphate of copper and aluminum that forms in arid regions where acidic, copper-rich water seeps through rocks containing aluminum and phosphorus minerals. This process occurs over millions of years, with the water depositing turquoise in veins and nodules. Major sources include the United States, China, Iran, and Egypt. In the Southwestern United States, turquoise mining has been a cultural and economic activity for centuries. Archaeological evidence shows that Native Americans were using turquoise over 2,000 years ago, crafting beads, pendants, and intricate inlay work that remains a vital part of Southwestern culture today.
Gemological Properties
Due to its opacity, turquoise is almost exclusively cut into cabochon shapes. Cabochon cutting involves polishing the stone into a smooth, rounded dome rather than faceting it, which maximizes the visual impact of its color and any characteristic matrix (the host rock pattern). The hardness of turquoise on the Mohs scale is relatively low, typically between 5 and 6, making it susceptible to scratching. It has no cleavage, meaning it does not have natural planes of weakness, but it is porous and can be prone to breakage. To enhance durability and color, turquoise is often stabilized with resins or wax, a common industry practice that should be disclosed at the point of sale.
Cultural and Metaphysical Significance
For thousands of years, turquoise has been revered as a protective talisman and a symbol of health and good fortune. In many cultures, it was believed to ward off evil and bring prosperity. Its association with the sky and water linked it to concepts of life and renewal. Today, it remains a popular stone in jewelry, particularly when set in sterling silver, and is often associated with Southwestern and Native American artistic traditions. While not explicitly detailed in the provided sources, its enduring symbolism is evident in its continued use in cultural artifacts and modern jewelry.
Zircon: The Brilliant Fire of the December Sky
Zircon is a gemstone known for its exceptional brilliance and fire, often compared to that of a diamond. It is a naturally occurring mineral, zirconium silicate (ZrSiO₄), and should not be confused with cubic zirconia, a synthetic diamond simulant. As a December birthstone, zircon offers a transparent, often colorless, or blue variety that provides a stark contrast to the opacity of turquoise.
Geological Formation and Sources
Zircon is one of the oldest minerals on Earth, with crystals found in sediments dating back billions of years. It forms in igneous and metamorphic rocks, and its durability makes it common in alluvial deposits (river beds) where it survives weathering. Major sources for gem-quality zircon include Australia, Cambodia, Myanmar, and Sri Lanka. Australia is particularly known for producing brownish zircon, which is heat-treated to achieve a vibrant blue color, the most popular shade for jewelry.
Gemological Properties
Zircon is prized for its high refractive index and strong dispersion, which give it exceptional brilliance and a fiery play of color. On the Mohs scale, zircon has a hardness of 6.5 to 7.5, making it relatively durable, though it can be brittle due to its perfect cleavage in two directions. This cleavage means that zircon can split along internal planes if struck with sufficient force, requiring careful handling during cutting and setting. It is typically faceted to maximize its light performance, resulting in sparkling gems suitable for rings and earrings. While blue is the most common color for December, zircon also occurs in yellow, green, and red hues.
Symbolism and Modern Appeal
Zircon’s diamond-like appearance has made it a popular and affordable alternative to diamonds. Historically, it has been associated with wisdom, honor, and purity. Its inclusion as a December birthstone adds a layer of brilliance and clarity to the month’s palette. The gem’s ability to produce a spectacular light show, combined with its natural occurrence, makes it a compelling choice for those seeking a traditional yet sparkling birthstone.
Tanzanite: The Modern Blue Marvel
Tanzanite is the newest addition to the December birthstone trio, discovered in 1967 in the Merelani Hills of Tanzania. Its introduction to the birthstone list in 1982 by the American Gem Trade Association marked the first change to the modern U.S. list in 50 years. This single-source gemstone is a variety of the mineral zoisite and is prized for its intense, saturated blue-violet color.
Geological Formation and Sources
Tanzanite’s formation is a geological rarity. It is believed to have been created under unique conditions during a metamorphic event that affected the rocks in the Merelani region. The process involved the interaction of heat, pressure, and specific mineral compositions, resulting in the blue variety of zoisite. Tanzanite is found in only one known location in the world: the Merelani Hills near Mount Kilimanjaro in Tanzania. This extreme rarity contributes to its value and allure.
Gemological Properties
Tanzanite exhibits a strong trichroic property, meaning it can display three different colors when viewed from three crystallographic directions: blue, violet, and burgundy. Most tanzanite on the market has been heat-treated to enhance its blue color and reduce the violet or brownish tones, a standard and accepted industry practice. On the Mohs scale, tanzanite has a hardness of 6 to 7, but it possesses perfect cleavage, making it susceptible to breakage if not handled with care. It is typically faceted to showcase its vibrant color and clarity.
Cultural Significance and Rarity
As a modern gemstone, tanzanite lacks the ancient lore of turquoise but has quickly developed its own narrative as a symbol of unique beauty and singular origin. Its rarity is a key part of its identity; it is often described as a “generational gemstone,” as the known deposits are finite. This modernity, combined with its striking color, makes it a popular choice for contemporary jewelry and for those seeking a birthstone with a compelling origin story.
Comparative Gemological Properties
The three December birthstones differ significantly in their physical properties, which influence their use in jewelry, care requirements, and overall durability. The following table summarizes key characteristics based on the provided sources.
| Property | Turquoise | Zircon | Tanzanite |
|---|---|---|---|
| Mineral Family | Hydrous phosphate | Zirconium silicate | Calcium aluminum hydroxyl silicate (Zoisite) |
| Typical Color | Sky blue to blue-green, yellowish green | Colorless, blue (most common), yellow, green, red | Blue-violet (often heat-treated) |
| Hardness (Mohs) | 5 - 6 | 6.5 - 7.5 | 6 - 7 |
| Cleavage | None | Perfect in two directions | Perfect |
| Common Cut | Cabochon | Faceted | Faceted |
| Transparency | Opaque | Transparent to translucent | Transparent to translucent |
| Primary Sources | USA, China, Iran, Egypt | Australia, Cambodia, Myanmar, Sri Lanka | Tanzania (only) |
| Key Characteristic | Often contains a matrix (host rock) | High brilliance and fire (dispersion) | Strong trichroism (three colors) |
This comparison highlights the diversity within the December group. Turquoise offers an opaque, earthy aesthetic with historical depth. Zircon provides a brilliant, diamond-like sparkle with a wider range of natural colors. Tanzanite delivers a unique, saturated blue from a single, rare location. The choice among them depends on personal preference for color, style, and the desired balance between durability and delicacy.
Care and Cleaning Considerations
Proper care is essential to maintain the beauty of these gemstones, as their physical properties vary widely. Understanding each stone’s durability is key to ensuring its longevity in jewelry.
Turquoise requires the gentlest handling due to its lower hardness and porosity. It should be cleaned only with a soft, damp cloth and mild soap, avoiding harsh chemicals, ultrasonic cleaners, and steam, which can damage or discolor the stone. Store turquoise jewelry separately to prevent scratches from harder gems.
Zircon is relatively hard but has perfect cleavage, making it prone to chipping or splitting from a sharp impact. It should be protected from blows and stored carefully. Cleaning can be done with warm water, mild detergent, and a soft brush, but avoid thermal shock (sudden temperature changes) as it can cause fracturing. Ultrasonic and steam cleaners are not recommended.
Tanzanite, with its perfect cleavage and moderate hardness, is also vulnerable to damage. It is best cleaned with a soft brush, warm water, and a mild detergent. Avoid ultrasonic cleaners and steam, which can cause internal stress and breakage. Given its cleavage, it is advisable to set tanzanite in protective settings, such as bezels, for rings worn daily.
For all three stones, removing jewelry during physical activities, household chores, and exposure to cosmetics or perfumes will help preserve their appearance. When in doubt, consulting a professional jeweler for cleaning and inspection is the safest course of action.
Conclusion
The three birthstones of December—turquoise, zircon, and tanzanite—offer a remarkable spectrum of choices, united by their blue tones but distinguished by their unique histories, origins, and properties. Turquoise carries the weight of ancient tradition and cultural significance, particularly in the Americas. Zircon provides timeless brilliance and a fire that rivals diamonds, with a geology that spans billions of years. Tanzanite represents modern gemology, a rare and recent discovery that has captivated the world with its intense color and singular source.
For those born in December, this trio allows for a personal selection that can reflect individual style, from the earthy and opaque to the fiery and transparent. The evolution of the birthstone list to include these three gems underscores the dynamic nature of gemology and cultural tradition. Whether chosen for its historical lore, its dazzling brilliance, or its modern rarity, each of these December stones carries a distinct legacy, making them enduring symbols for those who claim them as their own.