For those born in the final month of the year, the birthstones of December offer a captivating spectrum of blue hues, from the serene sky-blue of turquoise to the brilliant fire of zircon and the unique violet-blue of tanzanite. These gemstones are not merely decorative; they carry deep historical roots, distinct geological origins, and a legacy of cultural symbolism that has evolved over centuries. This article delves into the three primary modern birthstones for December—turquoise, zircon, and tanzanite—exploring their unique characteristics, the paths they take from mine to market, and the enduring beliefs that have cemented their place in the world of gemology.
History and Lore
The tradition of assigning specific stones to calendar months has ancient origins, but the modern list we recognize today is a product of standardization efforts in the early 20th century. The National Association of Jewelers (now Jewelers of America) established the first official birthstone chart in the United States in 1912, creating a streamlined reference that has been widely adopted. Over the decades, this list has been updated to include new discoveries and market trends, with significant revisions occurring in 1952 and later in the 20th and 21st centuries. For December, the modern chart officially lists turquoise, zircon, and tanzanite, though historical and traditional charts have included other stones like lapis lazuli.
Turquoise: An Ancient Talisman
Turquoise holds one of the longest histories as a gemstone, with evidence of its use dating back over 2000 years in the Southwestern United States. Native American cultures, in particular, revered the stone, using it to create intricate beads, pendants, inlay work, and small sculptures. For these communities, turquoise was more than an adornment; it was an integral part of cultural and spiritual life, a tradition that continues to this day. The stone’s enduring popularity is partly due to its relative affordability compared to other precious gems, making genuine turquoise accessible to a broad audience. Its opaque nature and preference for a bright blue color have defined its traditional use, often set in sterling silver to enhance its natural beauty.
Zircon: The Diamond Impostor and Protector
Zircon is a gem that has often been mistaken for more expensive stones due to its high luster and dazzling fire, which can be remarkably similar to that of a diamond. This characteristic has made it a popular, and sometimes controversial, alternative. Historically, zircon has been associated with protection and wisdom. It is a durable stone, though it can be brittle, and its journey to becoming a December birthstone is part of the broader evolution of the modern birthstone chart. The addition of zircon, along with other stones, reflects a shift towards providing more color and variety for December-born individuals.
Tanzanite: The Modern Marvel
Tanzanite is the newest addition to the December birthstone family, a 20th-century discovery that brought a fresh, vibrant blue to the market. Its inclusion was a significant update to the birthstone list, marking a change after decades of stability. This single-source gemstone, found only in a small area of Tanzania, has quickly captivated the global market with its unique violet-blue hue and pleochroic properties. The story of tanzanite is one of modern gemology, demonstrating how new discoveries can influence tradition and consumer preference.
Geological Formation and Sources
Each of December’s birthstones forms under distinct geological conditions and is sourced from specific regions around the world, making their origins as diverse as their colors.
Turquoise
Turquoise is a hydrous phosphate of copper and aluminum. It forms in arid regions where acidic, copper-rich water percolates through aluminum-bearing rocks, depositing the mineral in nodules or veins. Its color, ranging from blue to blue-green to yellowish green, is directly influenced by the presence of copper (which imparts blue) and iron or chromium (which can shift the color to green). While historically significant in the Southwestern United States, modern sources include mines in Iran, Egypt, and China. The stone’s opacity is a key characteristic, leading to its typical cut as a cabochon, often in freeform shapes to maximize the use of the rough material.
Zircon
Zircon is a zirconium silicate (ZrSiO₄) and is one of the oldest minerals on Earth, found in igneous and metamorphic rocks. It forms in prismatic crystals and is known for its high refractive index and strong dispersion, which gives it its diamond-like fire. Major sources of gem-quality zircon include Cambodia, Sri Lanka, Thailand, Australia, and the United States. The stone can be heat-treated to enhance its color, often to produce a bright blue hue, which is popular in the market. Zircon is also a key mineral in geochronology due to its durability and ability to retain uranium and thorium.
Tanzanite
Tanzanite is a variety of the mineral zoisite, with the chemical formula Ca₂Al₃(SiO₄)₃(OH). It is found exclusively in the Merelani Hills of northern Tanzania, in a very small mining area. Its formation is linked to specific geological conditions involving the metamorphism of limestone and the presence of trace elements. The intense violet-blue color is caused by vanadium, and the stone’s trichroic nature—displaying blue, violet, and red hues depending on the crystal orientation—makes it a unique and challenging gem to cut. Due to its limited geographic occurrence, tanzanite is considered one of the rarest gemstones, with its value influenced by its scarcity.
Gemological Properties
Understanding the physical and optical properties of these gemstones is essential for identification, valuation, and care. The table below summarizes key gemological data for turquoise, zircon, and tanzanite based on established standards.
| Property | Turquoise | Zircon (Gem-Quality) | Tanzanite (Zoisite) |
|---|---|---|---|
| Chemical Formula | Hydrous copper/aluminum phosphate | ZrSiO₄ | Ca₂Al₃(SiO₄)₃(OH) |
| Crystal System | Triclinic | Tetragonal | Orthorhombic |
| Mohs Hardness | 5 - 6 | 6.5 - 7.5 | 6.5 - 7 |
| Refractive Index | 1.610 - 1.650 | 1.920 - 2.010 | 1.691 - 1.700 |
| Specific Gravity | 2.60 - 2.90 | 4.60 - 4.70 | 3.35 |
| Luster | Waxy to subvitreous | Adamantine (diamond-like) | Vitreous |
| Key Characteristics | Opaque, porous, often matrix-included. Color from copper/iron. | High dispersion ("fire"), often heat-treated. Can be brittle. | Strong pleochroism (trichroic). Color from vanadium. |
Hardness and Durability: Turquoise, with a Mohs hardness of 5-6, is relatively soft and susceptible to scratching and chemical damage (e.g., from cosmetics, lotions, or acids). Zircon and tanzanite are harder, ranking 6.5-7.5 and 6.5-7 respectively, making them more durable for jewelry, though zircon can be brittle and prone to chipping due to its perfect cleavage. This property is critical for setting and daily wear.
Color and Clarity: Color is the primary value driver for all three stones. For turquoise, a bright, even blue without dark matrix inclusions is most prized. Zircon’s value is greatly enhanced by its brilliance and fire, with blue being a popular color. Tanzanite’s vivid violet-blue is its hallmark, and clarity is important, as inclusions can diminish its beauty. Unlike transparent gemstones, turquoise is typically opaque, leading to its characteristic cabochon cuts.
Treatment and Synthesis: The gemological market includes both natural and treated stones. Zircon is frequently heat-treated to achieve stable blue colors. Tanzanite is almost always heat-treated to remove brownish hues and enhance its blue-violet color. Turquoise is sometimes stabilized with resins or waxes to improve durability and color, a common practice that must be disclosed. While lab-created versions of many gemstones exist, the sources indicate that lab-created turquoise is available for cost-conscious shoppers, though natural stones are preferred by many.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, December’s birthstones are steeped in symbolism and metaphysical lore, beliefs that have persisted from ancient times to the present day.
Turquoise: The Stone of Protection and Healing
Across cultures, turquoise has been revered as a protective talisman. In ancient Egypt, it was used in jewelry and burial masks, believed to offer protection in the afterlife. For Native American tribes, it is a sacred stone associated with the sky, water, and spiritual communication. It is often linked to healing, emotional balance, and warding off negative energy. Its connection to the color of the sky and water reinforces its symbolism of tranquility and clarity.
Zircon: Wisdom and Prosperity
Zircon has historically been associated with wisdom, honor, and purity. In some traditions, it is believed to promote spiritual growth and protect against harm. Its diamond-like appearance led to its use as a symbol of wealth and prosperity, though its affordability makes it accessible. The stone’s fire is seen as a metaphor for inner light and enlightenment.
Tanzanite: A Stone of Transformation
As a modern discovery, tanzanite has quickly accumulated its own metaphysical associations. It is often linked to spiritual awakening, intuition, and higher consciousness. Its unique color and single-source origin contribute to a narrative of rarity and transformation, making it a favorite for those seeking a gemstone with a contemporary yet profound meaning.
Care and Cleaning
Proper care is essential to maintain the beauty and integrity of these birthstones, and it varies significantly based on their physical properties.
Turquoise: Due to its porosity and low hardness, turquoise requires gentle handling. It should be cleaned only with a soft, damp cloth. Avoid exposing it to chemicals, including household cleaners, cosmetics, and even perspiration, which can cause discoloration. Store turquoise jewelry separately to prevent scratching. Its sensitivity to heat and light is also notable; prolonged exposure can cause fading or cracking.
Zircon: While harder, zircon has perfect cleavage, meaning it can split if struck with force. It is also sensitive to heat and sudden temperature changes, which can cause fracturing. Cleaning should be done with warm, soapy water and a soft brush. Ultrasonic cleaners and steam cleaners are not recommended, as they can cause damage. Due to its brittleness, zircon jewelry should be handled with care to avoid impacts.
Tanzanite: With a Mohs hardness of 6.5-7, tanzanite is moderately durable but can be scratched by harder materials. It is also susceptible to chipping due to its cleavage. Cleaning is best done with warm, soapy water and a soft brush. Avoid ultrasonic cleaners and steam cleaning, as the heat and vibrations can damage the stone. Given its value and rarity, professional cleaning and regular inspections of settings are advisable.
For all gemstones, it is good practice to remove jewelry during physical activities, when applying lotions or perfumes, and before swimming or cleaning. Proper storage in a soft-lined jewelry box or pouch will help protect them from scratches and environmental damage.
Conclusion
The birthstones of December—turquoise, zircon, and tanzanite—offer a remarkable journey through history, geology, and culture. From the ancient, protective talisman of turquoise to the brilliant, diamond-like fire of zircon and the modern, transformative allure of tanzanite, each stone tells a unique story. Their diverse origins, from the arid landscapes of the American Southwest to the volcanic soils of Tanzania and the ancient crust of the earth, highlight the incredible natural processes that create gemstones. While their gemological properties differ in hardness, clarity, and color, they share the common thread of being cherished for their beauty and symbolic power. Understanding their properties, history, and care requirements allows enthusiasts and collectors to appreciate these December gems not just as jewelry, but as pieces of the earth’s legacy, carrying the colors and stories of our planet into the modern world.