The final month of the year is uniquely represented by a trio of birthstones, each offering a distinct palette of color and character. December’s official birthstones are turquoise, tanzanite, and zircon, a combination established by the American Gem Society (AGS) and the Jewelers of America (JA) to provide a modern and diverse selection for those born in this winter month. This collection was formally adopted in 2002, adding tanzanite to the long-standing list of turquoise and zircon. These three stones, ranging from the ancient sky-blue of turquoise to the vivid violet-blue of tanzanite and the fiery brilliance of zircon, provide a rich spectrum for jewelry enthusiasts. This article explores the unique attributes, origins, and significance of each of December’s three birthstones, drawing upon established gemological knowledge and historical context.
Turquoise: The Ancient Sky Stone
Turquoise is arguably the most historically significant of December’s birthstones, with a legacy that spans millennia. Its name is derived from the French phrase pierre turquoise, meaning "Turkish stone," reflecting its historical trade route through Turkey to Europe. However, turquoise mining predates this nomenclature by thousands of years. The earliest evidence of turquoise mining and use dates back to ancient Egypt, where the stone was prized for its vibrant color and used in elaborate jewelry, including the burial mask of Tutankhamun. In the Americas, turquoise holds a particularly revered place in the cultural heritage of Native American tribes, especially the Pueblo peoples of the Southwest, who have mined and worked the stone for centuries. The stone from these regions, particularly from mines in Arizona and New Mexico, is often referred to as "American turquoise" and is celebrated for its characteristic matrix patterns.
The geological formation of turquoise is unique among gemstones. It is a hydrated phosphate of copper and aluminum, formed in arid regions where acidic, copper-rich groundwater percolates through rocks containing aluminum and phosphorus. Over geological time, this process results in the precipitation of turquoise, often filling veins and nodules in host rock. The presence of copper imparts the classic blue-to-green color, while iron can shift the hue toward green, and the host rock (matrix) creates the distinctive web-like patterns seen in many specimens.
Turquoise is graded primarily on its color, matrix, and hardness. The most valued color is an even, medium to dark "sky blue" or "robin's egg blue," free from greenish tints. The matrix—the host rock remnants—can be a black, brown, or golden brown webbing. In some varieties, like the prized "spiderweb" turquoise, the matrix is a prominent feature. From a gemological standpoint, turquoise is relatively soft, with a hardness of 5 to 6 on the Mohs scale. It is also porous and can be susceptible to chemicals, heat, and light, which can cause discoloration. This porosity is why many commercial turquoise stones are stabilized with resin or wax to enhance durability and color consistency. Natural, untreated turquoise is highly valued by collectors and connoisseurs.
Beyond its physical properties, turquoise is steeped in symbolism. Across cultures, it has been regarded as a protective talisman, believed to ward off evil and bring good fortune. Ancient Persian warriors adorned their horses and themselves with turquoise for protection in battle. For Native American cultures, it represents the sky and water, holding spiritual significance and connection to the natural world. In modern times, it is associated with tranquility, wisdom, and emotional balance, making it a popular choice for both everyday jewelry and statement pieces.
Tanzanite: A Modern Miracle
In stark contrast to the ancient heritage of turquoise, tanzanite is a relative newcomer to the gemstone world, discovered in the 20th century. Its story is one of modern gemological discovery and rapid rise to prominence. Tanzanite was first identified in 1967 near Mount Kilimanjaro in Tanzania, East Africa. The gem was initially mistaken for an esoteric mineral but was later recognized as a variety of the mineral zoisite. It was named "tanzanite" in honor of its country of origin by Tiffany & Co., which introduced the gem to the global market in 1968. The company’s marketing campaign, highlighting its rarity and unique color, was instrumental in its swift ascent to becoming one of the most sought-after blue gemstones.
Geologically, tanzanite is formed through a rare and complex process. It is found only in a small, four-square-kilometer mining area in the Merelani Hills of Tanzania, making it significantly rarer than diamond or sapphire. The formation is believed to have occurred during a massive metamorphic event associated with the formation of the East African Rift Valley. Heat and pressure transformed the original brownish zoisite crystals into the vibrant blue-violet variety we know as tanzanite. This single-source origin contributes to its value and allure, with experts estimating that the current supply may be depleted within decades.
Tanzanite is prized for its extraordinary trichroism—the property of displaying three different colors when viewed from three different crystal directions. In its natural state, tanzanite typically appears brownish, blue, or violet. The brownish hue is the result of iron impurities, which can be removed by a controlled heat treatment process, a standard industry practice that yields the intense blue-violet color consumers desire. This heat treatment is permanent and widely accepted, making treated tanzanite the norm in the market.
Gemologically, tanzanite is a relatively soft stone, with a hardness of 6.5 to 7 on the Mohs scale. It has a vitreous luster and is often cut in faceted forms to maximize its brilliance and color play. The most valuable tanzanite exhibits a deep, saturated violet-blue color, with the finest stones displaying a strong hue in the blue range. Its color is often described as a more vivid and complex blue than sapphire, with a unique violet undertone. Due to its relative softness and perfect cleavage (a tendency to split along certain planes), tanzanite requires careful handling and setting in protective jewelry, such as pendants or earrings, rather than rings that are subject to daily wear.
The symbolism of tanzanite is closely tied to its modern origin. It is often associated with new beginnings, transformation, and spiritual awakening. As a stone that underwent a dramatic transformation from brown to blue through heat, it is seen as a metaphor for personal growth and change. Its deep blue color is linked to the throat chakra, promoting clear communication and self-expression. For December-born individuals, tanzanite represents a unique and contemporary birthstone choice.
Zircon: The Fire and Brilliance
Zircon, the third birthstone for December, is often confused with the synthetic material cubic zirconia (CZ), but they are entirely different. Natural zircon is one of the oldest minerals on Earth, with some specimens dating back over 4 billion years. It is a zirconium silicate (ZrSiO₄) and is found in a variety of colors, but the most prized for jewelry is the blue variety, which is often heat-treated to enhance or create its color. Other natural colors include yellow, green, brown, and red. The red variety, known as hyacinth, is particularly rare and valuable.
Zircon has a rich history and was once considered a gemstone of great importance. In the Middle Ages, it was believed to promote sleep, bring prosperity, and ward off evil spirits. It was also used as a diamond simulant due to its high refractive index and strong dispersion (fire), which gives it a brilliance that can rival diamond. However, its relative softness and perfect cleavage make it more challenging to work with than diamond.
Geologically, zircon is a common accessory mineral in many igneous and metamorphic rocks. It is mined in various locations worldwide, including Australia, Sri Lanka, Thailand, Cambodia, and the United States. Australian zircon is particularly noted for its high-quality blue stones. The gem’s formation is often linked to granitic magmas and high-grade metamorphic rocks.
From a gemological perspective, zircon is notable for its exceptional optical properties. It has a high refractive index (1.92-1.98) and strong dispersion (0.039), which is higher than that of diamond (0.044), giving it a fiery, colorful sparkle. However, zircon is relatively soft, with a hardness of 6.5 to 7.5 on the Mohs scale, and it has perfect cleavage, making it susceptible to chipping if struck. This fragility, combined with its brilliance, makes it a gemstone that requires careful setting and handling. It is often used in earrings and pendants rather than rings for daily wear.
Blue zircon is typically created by heating brown zircon crystals to high temperatures (around 1000°C) in a controlled atmosphere. This process is permanent and results in a stunning blue color that can range from pale to deep, vivid blue. The most sought-after blue zircon is a vivid, medium to dark blue with high brilliance. Its color is distinct from sapphire and tanzanite, often with a greener or lighter blue undertone.
The symbolism of zircon is linked to its fire and brilliance. It is associated with purity, integrity, and wisdom. In some traditions, it is believed to enhance spiritual insight and promote prosperity. Its ancient status as a diamond simulant also ties it to themes of clarity and truth. For those born in December, zircon offers a gemstone with a deep historical legacy and a dazzling visual appeal.
Comparison of December's Birthstones
The three birthstones of December—turquoise, tanzanite, and zircon—offer a diverse range of options for jewelry buyers and gem enthusiasts. Each stone has its own unique set of properties, origins, and care requirements. The following table provides a comparative overview of their key gemological characteristics:
| Property | Turquoise | Tanzanite | Zircon (Blue) |
|---|---|---|---|
| Mineral Group | Hydrated phosphate of copper & aluminum | Variety of Zoisite | Zirconium silicate (ZrSiO₄) |
| Chemical Formula | CuAl₆(PO₄)₄(OH)₈·4H₂O | Ca₂Al₃(SiO₄)₃(OH) | ZrSiO₄ |
| Color | Sky blue to green, often with matrix | Blue-violet (trichroic) | Blue (heat-treated from brown) |
| Hardness (Mohs) | 5 - 6 | 6.5 - 7 | 6.5 - 7.5 |
| Crystal System | Triclinic | Orthorhombic | Tetragonal |
| Refractive Index | 1.61 - 1.65 | 1.69 - 1.70 | 1.92 - 1.98 |
| Dispersion | Low | Low | High (0.039) |
| Origin | Arid regions (e.g., Iran, USA, China) | Single source: Tanzania, East Africa | Various (e.g., Australia, Sri Lanka) |
| Care & Cleaning | Sensitive to chemicals, heat, light; avoid ultrasonic cleaners. | Protect from blows due to perfect cleavage; avoid ultrasonic cleaners. | Avoid blows due to perfect cleavage; avoid ultrasonic cleaners. |
Care and Cleaning for December Birthstones
Proper care is essential to maintain the beauty and longevity of these gemstones, given their varying hardness and physical properties.
Turquoise: Due to its porosity and relative softness, turquoise requires gentle care. It should be cleaned with a soft, damp cloth and mild soap. Avoid all chemicals, including household cleaners, perfumes, and hairspray, as they can damage or discolor the stone. Turquoise should also be protected from prolonged exposure to direct sunlight and heat, which can cause fading or cracking. It is best to remove turquoise jewelry before swimming, bathing, or engaging in vigorous physical activity. Ultrasonic cleaners and steam cleaning are not recommended.
Tanzanite: With a hardness of 6.5 to 7 and perfect cleavage, tanzanite is more durable than turquoise but still requires careful handling. It is best cleaned with warm, soapy water and a soft brush. Avoid ultrasonic cleaners, as the vibrations can cause the stone to crack along its cleavage planes. Sudden temperature changes should also be avoided. Given its cleavage, tanzanite is best set in protective settings like bezels for rings or used in pendants and earrings to minimize impact.
Zircon: Zircon has a hardness of 6.5 to 7.5 but is brittle due to its perfect cleavage. It should be cleaned with warm, soapy water and a soft brush. Ultrasonic cleaners are not recommended, as they can cause chipping or cracking. Zircon jewelry should be stored separately to avoid scratching by harder stones. When wearing zircon rings, it is advisable to remove them during activities that could subject the stone to impact.
Conclusion
December’s trio of birthstones—turquoise, tanzanite, and zircon—provides a remarkable spectrum of color, history, and symbolism. From the ancient, protective talisman of turquoise to the modern, transformative story of tanzanite and the fiery, brilliant legacy of zircon, each stone offers a unique connection to the natural world and human culture. For individuals born in December, this selection allows for a personal choice that aligns with their style, values, and appreciation for gemstone heritage. Whether drawn to the serene sky-blue of turquoise, the vivid violet-blue of tanzanite, or the sparkling fire of zircon, the December birthstones are a testament to the enduring beauty and diversity of the mineral kingdom.