The final month of the year is associated with two distinct and captivating gemstones: the vibrant blue-violet tanzanite and the brilliant, fiery zircon. While traditional lists may vary, modern birthstone charts, particularly those from authoritative institutions like the American Gem Society (AGS) and the Gemological Institute of America (GIA), recognize both as December’s primary stones. Their striking blue hues, reminiscent of winter skies and deep oceans, make them exceptionally popular for fine jewelry, especially when set in the cool, luminous elegance of white gold. This article delves into the characteristics, symbolism, and practical considerations for these December birthstones, drawing from contemporary jewelry market data to provide a comprehensive overview for enthusiasts, collectors, and those seeking meaningful adornments.
The choice between tanzanite and zircon is not merely one of color but of origin, durability, and personal significance. Tanzanite, a relative newcomer to the gem world, offers a unique trichroic property that displays shades of blue, violet, and burgundy, captivating a modern audience with its rarity and vivid color. Zircon, one of the oldest minerals on Earth, boasts a brilliant luster and a history that spans centuries, offering a classic sparkle with exceptional clarity. Both stones are frequently mounted in 14-karat white gold, a popular choice for its hypoallergenic qualities, durability, and ability to enhance the gemstone’s color without competing with it. This pairing creates a timeless aesthetic that suits both everyday wear and special occasions, from delicate stud earrings to more elaborate pendants and rings.
Understanding the properties and lore of these stones allows buyers and wearers to appreciate them beyond their visual appeal. The following sections explore their geological origins, gemological specifications, cultural symbolism, and practical care, providing a detailed guide rooted in the available data from the current jewelry market. This analysis focuses on the specific offerings found in contemporary retail environments, highlighting the materials, designs, and specifications that define modern December birthstone jewelry.
Historical and Cultural Significance
The journey of December’s birthstones to their modern status is a tale of both ancient tradition and recent discovery. Tanzanite is the newest of the major gemstones, first identified in 1967 in the Merelani Hills of Tanzania. Its rapid rise to prominence is a testament to its exceptional beauty. Initially marketed under the name "tanzanite" by the Tiffany & Co. jewelry house in 1968, it was immediately celebrated for its intense, saturated blue color, which was unlike any other gem on the market. The gem’s association with Tanzania, its sole source, adds to its allure and mystique. While it lacks the millennia-long history of gems like diamond or sapphire, its status as a modern birthstone is firmly established, symbolizing a sense of new beginnings and contemporary elegance. It is often linked to the 24th wedding anniversary, a more recent tradition that underscores its place in modern sentimental gifting.
In contrast, zircon holds a much deeper historical footprint. It is one of the oldest minerals on Earth, with zircon crystals found in Australian sediments dating back over 4.4 billion years. For centuries, it has been mistaken for diamond due to its high refractive index and brilliance, earning it the nickname "jacinth" in historical texts. During the Middle Ages, it was believed to promote rest, ward off evil spirits, and bring prosperity. Its use in jewelry spans cultures, from ancient Egypt to medieval Europe. The blue variety of zircon, which is the color most associated with December, is created through heat treatment of brown zircon crystals, a process that has been refined over decades. Its recognition as a December birthstone is more traditional than tanzanite’s, appearing in the modern birthstone list established in 1912 by the National Association of Jewelers (now Jewelers of America), which has been periodically updated.
The modern birthstone list, as reflected in contemporary jewelry catalogs, often includes both stones, offering consumers a choice. This duality allows for personal preference—whether one is drawn to the historic sparkle of zircon or the vibrant, unique color of tanzanite. The symbolism attached to each stone further differentiates them. Tanzanite is sometimes associated with transformation, intuition, and spiritual awakening, a belief that aligns with its dramatic geological formation and sudden appearance in the gem market. Zircon, with its ancient origins, is often linked to wisdom, purity, and protection. These attributions, while metaphysical, add a layer of meaning that enhances the gemstone’s value as a personal talisman or a meaningful gift, particularly for those born in December.
Geological Formation and Mining Sources
The origins of these gemstones are as distinct as their appearances. Tanzanite is a variety of the mineral zoisite, specifically the blue to violet-blue form. Its formation is exceptionally rare, requiring a unique geological combination. It is found in a single, small mining area in the Merelani Hills of Tanzania, near the base of Mount Kilimanjaro. This limited geographic source—often described as covering only a few square miles—contributes significantly to its rarity and value. The gem is formed from the metamorphism of limestone, with heat and pressure from tectonic activity causing the introduction of vanadium, which imparts the stone’s characteristic blue color. Mining operations are relatively small-scale, often relying on artisanal methods, which means supply is finite and subject to the challenges of a single location. This geographic exclusivity is a key factor in its market positioning and pricing.
Zircon is a zirconium silicate (ZrSiO₄) and is found in a wide variety of geological environments worldwide. It is a common accessory mineral in igneous and metamorphic rocks and is often recovered as a byproduct of mining for other minerals. Significant sources include Australia, which produces a large portion of the world’s commercial zircon, as well as Cambodia, Sri Lanka, Thailand, and Brazil. Unlike tanzanite, zircon is not exclusive to one location. The blue variety used in jewelry is typically produced by heating naturally brown zircon crystals, a process that can be performed in controlled laboratory settings. This treatment is stable and widely accepted in the gem trade, making blue zircon a readily available and affordable option. The global distribution of zircon sources means it is less susceptible to supply chain disruptions than tanzanite, contributing to its consistent presence in the jewelry market.
The mining and processing of these stones differ significantly. Tanzanite mining in Tanzania is often conducted by small-scale miners who sell their rough to larger cutting facilities. The stones are then cut and polished, with the color being natural and not enhanced through heat treatment (though some tanzanite may be lightly heated to remove brownish tones, this is considered a standard practice). For blue zircon, the process involves selecting high-quality brown zircon crystals and subjecting them to controlled heating, which can reach temperatures of up to 1,000 degrees Celsius. This treatment is permanent and does not affect the gem’s durability. Both stones are then cut into various shapes—round, oval, pear, and more—to maximize their brilliance and color in finished jewelry.
Gemological Properties
Understanding the physical and optical properties of these gemstones is crucial for appreciating their value and ensuring proper care. The following table summarizes key gemological data for tanzanite and blue zircon, based on standard gemological references.
| Property | Tanzanite | Blue Zircon |
|---|---|---|
| Chemical Formula | Ca₂Al₃(SiO₄)₃(OH) | ZrSiO₄ |
| Crystal System | Orthorhombic | Tetragonal |
| Hardness (Mohs) | 6.5 – 7 | 6.5 – 7.5 |
| Refractive Index | 1.691 – 1.700 | 1.92 – 1.98 |
| Specific Gravity | 3.35 – 3.38 | 4.6 – 4.7 |
| Durability | Fair to good; can be brittle | Good; can be brittle |
| Treatment | Minor heat treatment possible | Heat treatment standard for blue color |
| Optical Character | Trichroic (shows three colors) | High luster, double refraction |
Tanzanite is known for its trichroic property, meaning it displays three different colors when viewed from different crystal directions: typically blue, violet, and burgundy or reddish-brown. The most desirable color is an intense, pure violet-blue. With a hardness of 6.5 to 7 on the Mohs scale, it is suitable for most jewelry but requires careful handling to avoid scratches and impacts. Its refractive index is moderate, contributing to a pleasing luster, but its relatively low specific gravity makes it feel lighter than other gems of similar size. Tanzanite is often found in larger carat weights, making it an excellent choice for statement pieces.
Blue zircon is renowned for its exceptional brilliance and fire, rivaling that of diamond due to its high refractive index and strong dispersion (the ability to split light into spectral colors). Its hardness ranges from 6.5 to 7.5, making it slightly more durable than tanzanite, though it can still be brittle and prone to chipping if struck hard. The gem is typically very clean, with inclusions being rare, which enhances its clarity and sparkle. The specific gravity is significantly higher than tanzanite’s, giving it a substantial feel. The blue color in commercial zircon is consistently achieved through heat treatment of brown crystals, resulting in a stable and vivid hue. Zircon is available in a wide range of sizes, from small melee stones to larger center gems.
When set in 14-karat white gold, both gemstones are protected by a durable metal alloy. White gold, an alloy of gold with white metals like palladium or nickel, is often plated with rhodium to enhance its whiteness and provide an extra layer of protection. In the provided jewelry examples, the use of 14kt white gold is standard, offering a good balance of purity (58.3% gold) and strength. The settings for December birthstone earrings typically feature secure prong or bezel settings to hold the gemstone firmly. For example, the specifications from the retail sources mention stud earrings with butterfly backs, post lengths of 6-10mm, and gem sizes of 2mm to 3mm, indicating designs intended for comfort and daily wear.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, December birthstones are imbued with rich symbolism and metaphysical beliefs that have evolved over time and across cultures. These associations, while not scientifically verified, add a layer of meaning that many wearers find compelling.
Tanzanite, as a modern gemstone, has developed symbolic meanings that reflect its unique story. It is often called the "stone of transformation," believed to facilitate a higher consciousness and spiritual awareness. Its striking trichroism is seen as a metaphor for seeing multiple perspectives or unlocking hidden truths. Some metaphysical traditions associate tanzanite with the crown chakra, linking it to intuition, clarity, and communication with higher realms. Given its origin near Mount Kilimanjaro, it is also sometimes connected to the energy of Africa and the grounding power of the earth. For those born in December, tanzanite is thought to bring calm, balance, and a sense of purpose, making it a popular choice for jewelry meant to inspire personal growth.
Zircon, with its ancient history, carries a more traditional set of beliefs. In many cultures, it has been regarded as a stone of protection, purity, and prosperity. Its brilliance was believed to ward off evil spirits and protect travelers. During the Renaissance, it was thought to promote honor and wisdom in the wearer. The blue variety, in particular, is associated with peace, tranquility, and clarity of thought. Some believe that wearing zircon can help alleviate insomnia, reduce nightmares, and bring about a restful state. As a December birthstone, it symbolizes the clarity of winter and the promise of renewal, aligning with its sparkling, icy appearance. These beliefs are rooted in historical lore and continue to be referenced in contemporary gemstone guides.
It is important to note that these metaphysical properties are part of cultural and personal belief systems and are not recognized by mainstream gemological science. However, for many jewelry buyers, these symbolic meanings enhance the emotional value of the gemstone, transforming it from a mere accessory into a meaningful heirloom or a personal talisman. The choice between tanzanite and zircon may therefore be influenced not only by color preference but also by the symbolic resonance each stone holds for the individual.
Care and Cleaning for December Birthstones
Proper maintenance is essential to preserve the beauty and longevity of any gemstone jewelry. The care requirements for tanzanite and blue zircon differ slightly due to their distinct physical properties, though both benefit from gentle handling.
Tanzanite, with its hardness of 6.5 to 7 and fair toughness, requires careful attention to avoid scratches and impacts. It is softer than quartz (hardness 7) and can be damaged by harder materials. To clean tanzanite jewelry, use a soft brush, mild soap, and lukewarm water. Avoid ultrasonic cleaners and steam cleaners, as the vibrations and heat can cause fractures in the stone, especially if it has any existing inclusions. It is also advisable to remove tanzanite rings or bracelets before engaging in physical activities or household chores to prevent hard blows. When storing, keep it separate from other jewelry to prevent scratches, ideally in a soft-lined compartment or pouch.
Blue zircon, while slightly harder (6.5 to 7.5), is known for its brittleness, meaning it can chip or crack under impact despite its higher hardness. It is also sensitive to rapid temperature changes. Cleaning should be done with a soft cloth, mild detergent, and lukewarm water, using a soft brush to gently remove dirt from behind the setting. As with tanzanite, ultrasonic and steam cleaners are not recommended due to the risk of thermal shock and physical stress. It is best to put on zircon jewelry last when dressing and remove it first when undressing to minimize exposure to chemicals, perfumes, and cosmetics, which can dull its surface over time.
For both gemstones set in 14-karat white gold, regular inspection of the setting is crucial. The prongs or bezels that hold the gemstone can wear down over time, potentially leading to a lost stone. It is advisable to have the jewelry professionally checked and cleaned by a jeweler annually. When not in use, store each piece separately in a fabric-lined box to prevent scratching and tangling. By following these care guidelines, owners can ensure that their December birthstone jewelry remains vibrant and secure for generations.
Conclusion
The December birthstones, tanzanite and blue zircon, offer a captivating blend of modern allure and ancient heritage. Tanzanite’s exclusive origin and mesmerizing trichroic color make it a gemstone of the 20th century, symbolizing transformation and spiritual insight. Blue zircon, with its diamond-like brilliance and centuries-old legacy, represents purity, protection, and clarity. Both stones, when set in the elegant and durable medium of 14-karat white gold, create jewelry that is both visually striking and deeply meaningful.
The choice between them ultimately rests on personal preference—whether one is drawn to the rare, vibrant hues of tanzanite or the classic, fiery sparkle of zircon. Their gemological properties, while requiring careful handling, ensure that they remain cherished possessions when properly maintained. As symbols of the winter month, these gems capture the essence of December: a time of reflection, celebration, and the promise of renewal. For those born in this month or for anyone seeking a gift of significance, December’s birthstones provide a timeless connection to the natural world’s beauty and the rich tapestry of human culture.