Introduction
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 choice of gemstones, each with its own rich history, geological origin, and symbolic significance. While turquoise has been revered for millennia as a talisman of protection and good fortune, the more recent addition of tanzanite brings a story of modern discovery and rarity, and zircon, one of the oldest minerals on Earth, offers a spectrum of color and a deep historical legacy. This article explores the geological properties, historical journeys, and cultural meanings of these three remarkable gemstones, drawing from documented sources to provide a comprehensive overview for enthusiasts and collectors alike. We will examine how these stones transitioned from ancient lore to their modern status as December's birthstones, and provide practical guidance for their care.
History and Lore: From Ancient Talismans to Modern Treasures
The history of December's birthstones is a tale of ancient traditions and contemporary discovery. Turquoise, in particular, carries a legacy that spans continents and millennia.
The Ancient Legacy of Turquoise
Turquoise is the oldest gemstone in the December trio, with a documented history of use that stretches back over 6,000 years. It has been found in artifacts from ancient Egypt, Mesopotamia, and the Americas. The stone was not merely decorative; it was deeply embedded in cultural and spiritual practices. Ancient Egyptians, for instance, adorned themselves with turquoise jewelry and inlaid it into burial masks, believing it offered protection in the afterlife. The name "turquoise" itself is derived from the French "pierre tourques," meaning "Turkish stone," reflecting its introduction to Europe via Turkish traders. Its reputation as a stone of good fortune and protection is a consistent thread through history, making it a perennial favorite for amulets and talismans.
The Modern Discovery of Tanzanite
In stark contrast to turquoise's ancient origins, tanzanite is a gemstone of the modern era. Its story began in 1967, when it was discovered in the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. The gem was initially misidentified as zircon but was later recognized as a distinct variety of the mineral zoisite. Its unique, vibrant blue-violet hue, which can range from ultramarine to pale lavender, was unlike any other gemstone on the market. This striking color, combined with its limited geographic source, quickly made it a sensation in the gem trade. De Beers marketed the stone extensively, and by 1970, it was officially recognized as a birthstone for December. Its discovery is a testament to the ongoing evolution of gemological knowledge and the global trade.
The Dual Identity of Zircon
Zircon is one of the oldest minerals on Earth, with some crystals dating back over 4.4 billion years. Its history as a gemstone is equally long, having been used in jewelry since the Middle Ages. However, its journey to becoming a December birthstone is intertwined with a persistent case of mistaken identity. For centuries, zircon was often confused with diamond due to its high refractive index and brilliance, leading to its use as a diamond simulant. This confusion is reflected in its name, which is derived from the Persian "zargun," meaning "gold-colored." While zircon is naturally found in a variety of colors, including yellow, green, red, and brown, the blue variety is the most popular for jewelry and is the one typically associated with December. Its recognition as a birthstone is a nod to its historical significance and enduring beauty.
Geological Formation and Sources
The three December birthstones originate from vastly different geological processes and are mined in distinct regions of the world.
Turquoise: A Hydrated Phosphate Mineral
Turquoise is not a single mineral but a hydrous phosphate of copper and aluminum. Its formation requires a specific geological environment where acidic, copper-rich water percolates through rocks containing aluminum and phosphorus. Over long periods, these solutions deposit turquoise in veins, nodules, or as a matrix within host rocks like sandstone or limestone. The most prized turquoise comes from Iran (historically known as Persian turquoise), which is renowned for its uniform, robin's-egg blue color and lack of matrix. Other significant sources include the Southwestern United States (Arizona, New Mexico, Nevada), China, and Egypt. The color is directly influenced by the amount of copper (blue) and iron (green) present in the mineral.
Tanzanite: A Gemstone of a Single Source
Tanzanite is a variety of the mineral zoisite, colored by vanadium. Its formation is linked to a unique geological event: the metamorphism of rocks during the formation of the East African Rift. This event caused the heating and alteration of pre-existing rocks, allowing vanadium to be incorporated into the zoisite crystal structure, resulting in its signature blue-violet color. The Merelani Hills in Tanzania remain the only commercial source of tanzanite in the world. This extreme rarity—geologists estimate that the current supply could be exhausted within a few decades—contributes significantly to its value and desirability. The stone's color is also heat-sensitive; most tanzanite on the market has been heat-treated to enhance its blue hue, a process that is considered permanent and stable.
Zircon: A Durable Silicate Mineral
Zircon is a zirconium silicate (ZrSiO₄) and is one of the hardest natural minerals, with a Mohs hardness of 7.5. It forms in igneous rocks, particularly in granites and pegmatites, and can also be found in metamorphic rocks. As an accessory mineral, it often appears as small, prismatic crystals. Zircon is mined in several countries, including Australia (the leading producer of gem-quality zircon), Cambodia, Sri Lanka, and Tanzania. The blue variety of zircon, which is the most popular for December, is typically achieved through heat treatment of brown or yellow zircon. This process, known as annealing, is a standard and accepted industry practice that permanently changes the crystal's color to a stable blue.
Gemological Properties: A Comparative Overview
Understanding the physical and optical properties of these gemstones is crucial for identification, valuation, and care. The table below summarizes key gemological data for turquoise, tanzanite, and zircon, based on standard gemological references. It is important to note that the provided sources do not contain detailed gemological data such as refractive index or specific gravity; therefore, this table is presented for comparative context, highlighting the distinct characteristics of each stone.
| Property | Turquoise | Tanzanite | Zircon (Blue) |
|---|---|---|---|
| Chemical Formula | Hydrous phosphate of Cu & Al | Ca₂Al₃(SiO₄)₃(OH) | ZrSiO₄ |
| Crystal System | Triclinic | Orthorhombic | Tetragonal |
| Mohs Hardness | 5 - 6 | 6.5 - 7 | 7.5 |
| Refractive Index | 1.61 - 1.65 | 1.69 - 1.70 | 1.92 - 2.01 |
| Specific Gravity | 2.6 - 2.9 | 3.35 | 4.6 - 4.7 |
| Luster | Waxy to dull | Vitreous to adamantine | Vitreous to adamantine |
| Color | Blue to greenish-blue | Blue to violet-blue | Blue (heat-treated) |
| Notable Features | Often porous, can be dyed or stabilized | Highly pleochroic (shows different colors from different angles) | High refractive index, very brilliant |
Color, Clarity, and Cut
Turquoise is prized for its uniform, opaque blue to greenish-blue color. Its quality is often assessed by its color and texture; the finest grades are "spiderweb" matrix-free stones from Iran. Turquoise is often stabilized (treated with resin or wax) to improve durability and color, a common and accepted practice. Tanzanite is celebrated for its intense, saturated blue-violet color. It is a strongly pleochroic gemstone, meaning it displays different colors (typically blue, violet, and red-brown) when viewed from different angles. Gem cutters orient the stone to display the desired blue-violet hue. Clarity is important, as inclusions can affect the stone's brilliance. Zircon is valued for its exceptional brilliance and fire, which rival that of diamond. The blue variety is typically eye-clean, with minimal inclusions. Its high refractive index makes it a spectacular gem when cut properly, often in faceted styles like round brilliants or princess cuts.
Symbolism and Metaphysical Beliefs
The symbolism attached to these birthstones is as diverse as their origins.
Turquoise: The Stone of Protection
Turquoise has long been associated with protection, healing, and good fortune. In many cultures, it was believed to ward off evil spirits and bring safety to travelers. Native American tribes, such as the Navajo and Zuni, consider turquoise a sacred stone, symbolizing life, health, and the connection to the sky and water. It is also linked to communication and emotional balance, said to promote inner calm and truth.
Tanzanite: The Stone of Transformation
As a relatively new gemstone, tanzanite's metaphysical associations are modern. It is often called the "stone of transformation" and is believed to facilitate a higher consciousness, intuition, and spiritual perception. Its unique color, which appears to change with the light, is seen as symbolic of its ability to bridge the mundane and the spiritual. It is also associated with compassion and calmness.
Zircon: The Stone of Wisdom and Honor
Zircon, particularly the blue variety, is associated with wisdom, honor, and purity. Historically, it was believed to promote sleep, ward off nightmares, and bring prosperity. Its durability and brilliance have made it a symbol of steadfastness and integrity. In some traditions, it is thought to enhance self-confidence and aid in meditation.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of these gemstones, given their varying physical properties.
Turquoise Care
With a Mohs hardness of only 5-6, turquoise is relatively soft and porous. It is susceptible to scratching, chipping, and chemical damage. Avoid exposing turquoise to harsh chemicals, including perfumes, lotions, and household cleaners. Clean it only with a soft, damp cloth and mild soap. Never use ultrasonic or steam cleaners, as they can cause cracking or discoloration. Store it separately from harder gemstones to prevent scratches.
Tanzanite Care
Tanzanite has a hardness of 6.5-7, making it moderately durable but still prone to chipping due to its cleavage. It is best suited for jewelry that is not subjected to hard wear, such as earrings or pendants. Clean tanzanite with warm, soapy water and a soft brush. Avoid sudden temperature changes and ultrasonic cleaners, which can cause damage. Store it in a soft cloth or separate compartment to protect it from scratches.
Zircon Care
Zircon is a hard and durable gemstone (Mohs hardness 7.5), but it can be brittle due to its crystal structure. It is relatively safe for most types of jewelry, including rings, but care should be taken to avoid sharp blows. Clean zircon with warm, soapy water and a soft brush. It is generally safe for ultrasonic cleaners, but caution is advised if the stone has inclusions or fractures. Avoid exposure to strong heat, as some zircon (especially brown varieties) may have undergone heat treatment that could be reversed.
Conclusion
December's birthstones—turquoise, zircon, and tanzanite—offer a remarkable spectrum of color, history, and meaning. From the ancient, protective talisman of turquoise to the brilliant, durable allure of zircon and the modern, transformative story of tanzanite, each stone provides a unique connection to the natural world and human culture. Their selection is not merely a matter of personal preference but an engagement with geological wonders that have been formed over millions of years. Understanding their origins, properties, and care ensures that these gemstones can be appreciated and preserved for generations, continuing their legacy as symbols of good fortune, wisdom, and beauty for those born in the final month of the year.