The month of December is uniquely represented by three distinct birthstones: turquoise, zircon, and tanzanite. Each of these gems offers a unique interpretation of the color blue, ranging from the opaque, sky-blue of turquoise to the fiery brilliance of zircon and the captivating violet-blue of tanzanite. This trio provides a diverse palette for those born in the final month of the year, allowing for a choice that reflects personal style and preference. The selection is not merely aesthetic; each stone carries its own history, geological origin, and set of properties that influence its durability, care, and symbolic meaning. While all three are celebrated as December's birthstones, they vary significantly in hardness, cleavage, and common treatments, factors that are crucial for both jewelers and consumers to understand.
This article will explore the rich tapestry of the December birthstones, delving into their historical and cultural significance, the geological processes that form them, their distinct gemological properties, and the metaphysical beliefs associated with each. It will also provide practical guidance on their care and maintenance, ensuring that these beautiful stones can be enjoyed for generations to come.
History and Lore
The tradition of assigning specific stones to months has evolved over centuries, with modern lists being formalized in the 20th century. The December stones, in particular, have undergone notable changes to their official list.
Turquoise: An Ancient Protector
Turquoise boasts one of the longest histories as a gemstone, with evidence of its use dating back over 2000 years in the Southwestern United States, where Native American cultures crafted beads, pendants, and intricate inlay work. This deep historical integration makes turquoise an enduring symbol of Southwestern culture. Beyond its artistic applications, turquoise has been imbued with protective symbolism. It is traditionally regarded as a love charm and a symbol of good fortune and success. Beliefs held that turquoise could relax the mind and protect its wearer from harm, with turquoise rings specifically thought to ward off evil spirits. This protective quality aligns with its ancient role as a stone used to repel evil and protect eyesight, as indicated by its historical use in necklaces for these purposes.
Zircon: The Diamond Alternative
Zircon's history is closely tied to its remarkable optical properties. For centuries, it has been valued for its high luster and the colorful fire it produces, which is similar to that of a diamond. This resemblance led to zircon being used as an alternative stone for diamond in historical jewelry. Its journey to becoming a modern birthstone is more recent. Zircon was added to the official December birthstone list in 1952, replacing lapis lazuli. This change reflects the gemological community's ongoing effort to update birthstone lists with stones that are more readily available and suitable for modern jewelry. The most popular color for zircon today is blue, a hue often achieved through treatment, which has contributed to its widespread appeal.
Tanzanite: The Modern Marvel
Tanzanite is the newest addition to the December birthstone family, earning its place due to its stunning color and relative rarity. Unlike the ancient turquoise or historically significant zircon, tanzanite's story is one of modern discovery and rapid rise to prominence. Its captivating color, which shifts from blue to bluish purple to bluish violet depending on the viewing angle, has made it a favorite in contemporary jewelry. Most tanzanite sold in the market today has been heat-treated to achieve its desirable blue-to-violet hues. As the newest member of the trio, tanzanite represents the dynamic nature of the gemstone trade and the ongoing discovery of new and beautiful minerals for the world to enjoy.
Geological Formation and Sources
Understanding where these gemstones originate provides insight into their rarity and value. Each of the December stones forms under different geological conditions and is mined in specific regions around the world.
Turquoise: A Hydrated Copper Mineral
Turquoise is not a single mineral but a hydrous phosphate of copper and aluminum. Its formation requires a specific combination of elements—copper, aluminum, and phosphorus—mixing in the presence of water, typically in arid regions. This process is relatively rare, which contributes to the value of high-quality turquoise. The most historically significant sources for turquoise include the Southwestern United States, where it has been mined and used by indigenous cultures for millennia. Other notable sources include Iran (historically known as Persian turquoise), China, and Egypt. The color of turquoise, which ranges from blue to blue-green to yellowish green, is directly influenced by the amount of copper (blue) and iron (green/yellow) present in its formation.
Zircon: A Resilient Silicate
Zircon is a zirconium silicate (ZrSiO₄) and is one of the oldest minerals on Earth, with some crystals dating back billions of years. It forms in a variety of igneous and metamorphic rocks, most commonly in granites and pegmatites. The gem-quality zircon used in jewelry is mined in several locations worldwide. Key sources include Cambodia, Sri Lanka, and Australia, which are known for producing high-quality stones. The vibrant blue zircon popular in modern jewelry is typically the result of heating brown or yellowish natural zircon crystals. This heat treatment is a standard industry practice that enhances the stone's color without affecting its durability.
Tanzanite: A Single-Source Gemstone
Tanzanite is a variety of the mineral zoisite and is composed of calcium aluminum silicate. What makes tanzanite exceptionally rare is its geological origin; it is found in only one location on Earth: the Merelani Hills of Northern Tanzania. This single-source origin adds to its allure and value. The gemstone's formation is linked to a unique geological event—the heating of zoisite crystals by metamorphic processes. The resulting tanzanite crystals are then mined, and as with zircon, the vast majority undergo heat treatment to transform their naturally occurring brownish hues into the prized blue and violet colors seen in jewelry.
Gemological Properties
The physical and chemical properties of a gemstone determine its durability, how it should be cut, and how it must be cared for. The December birthstones display a wide range of these characteristics.
Hardness and Durability
Gemological hardness is measured on the Mohs scale, where 1 is the softest (talc) and 10 is the hardest (diamond). This scale is critical for understanding a stone's resistance to scratching.
- Turquoise has a hardness of 5 to 6 on the Mohs scale. This relatively low hardness means it is susceptible to scratching and abrasion. It is also porous, which can affect its color and durability over time, especially if exposed to chemicals or oils.
- Zircon is significantly harder, with a hardness of 7.5. This makes it more resistant to scratching than turquoise and suitable for various jewelry types, though it can be brittle.
- Tanzanite has a hardness of 6.5 to 7. While harder than turquoise, it is still less durable than many other gemstones and requires careful handling to avoid chipping or scratching.
The following table summarizes the key hardness and durability ratings for the December birthstones, as well as other notable gems for context, based on industry classifications:
| Gemstone | Month(s) | Mohs Hardness | Durability Rating | Key Vulnerabilities |
|---|---|---|---|---|
| Turquoise | December | 5 - 6 | Fair to Poor | Low hardness, easily scratched |
| Zircon | December | 7.5 | Fair to Poor | Prone to breakage |
| Tanzanite | December | 6.5 - 7 | Fair to Poor | Perfect cleavage, breaks easily |
| Diamond | April | 10 | Excellent | None (hardest natural material) |
| Sapphire | September | 9 | Excellent | None |
| Emerald | May | 7.5 - 8 | Fair to Poor | Prone to breakage |
| Opal | October | 5 - 6.5 | Fair to Poor | Low hardness, easily scratched |
Cleavage and Toughness
Cleavage refers to a mineral's tendency to break along flat planes of weakness. Stones with "perfect" cleavage are particularly vulnerable to breaking if struck.
- Turquoise does not have distinct cleavage, but its low hardness and porosity make it vulnerable to damage.
- Zircon has poor cleavage, which means it is more likely to fracture irregularly than to break along a clean plane. However, it is still considered prone to breakage.
- Tanzanite has perfect cleavage in one direction. This is a critical property, as it means the stone can break easily if subjected to a sharp blow, making it unsuitable for rings or bracelets that are prone to impact unless set in a protective mounting.
Color and Treatment
Color is one of the most important factors in a gemstone's value and appearance.
- Turquoise is prized for its sky-blue to blue-green color. Bright blue is the most preferred hue. Its opaque nature means it is almost always cut into cabochons (smooth, rounded domes) rather than faceted.
- Zircon is known for its high luster and "fire" (dispersion of light into spectral colors). Natural zircon is often yellow, red, or brown. The popular blue zircon is almost always the result of heat treatment applied to brown crystals. Approximately 80% of the zircon sold today is blue, a color achieved through this process.
- Tanzanite is defined by its trichroism—the ability to show different colors (blue, violet, and burgundy) from different crystal directions. The commercial blue to bluish-violet color seen in jewelry is produced by heat treatment, which removes the brownish tones found in most rough material.
Chemical Composition
- Turquoise: Hydrous copper aluminum phosphate (CuAl₆(PO₄)₄(OH)₈·4H₂O).
- Zircon: Zirconium silicate (ZrSiO₄).
- Tanzanite (Zoisite): Calcium aluminum silicate (Ca₂Al₃(SiO₄)₃(OH)).
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, gemstones have been attributed with symbolic meanings and metaphysical powers throughout history. These beliefs are part of the cultural lore surrounding each stone.
- Turquoise is deeply connected to protection and good fortune. It is regarded as a love charm and a symbol of success. Its historical use in warding off evil spirits and protecting the eyesight of the wearer underscores its role as a guardian stone. It is also believed to promote mental relaxation.
- Zircon carries the symbolism of purity and wisdom. Traditionally a favorite stone of priests and kings, it was believed to possess protective qualities, with legends stating that a venomous snake would die if placed in a vessel made of sapphire—a gemstone with which zircon was historically associated due to its similar appearance.
- Tanzanite, as a modern discovery, has accumulated contemporary metaphysical beliefs. It is often associated with transformation, spiritual awakening, and the opening of higher consciousness. Its unique color-changing property is sometimes linked to its ability to bridge different realms of thought and perception.
It is important to note that these symbolic meanings and metaphysical beliefs are part of cultural and historical tradition. They are not recognized by formal gemological science, which focuses on the physical and chemical properties of the stones. However, for many enthusiasts and buyers, these beliefs add a layer of personal significance to their gemstone choice.
Care and Cleaning
Proper care is essential to preserve the beauty and integrity of any gemstone, especially for those with lower hardness or perfect cleavage.
Turquoise Care
Due to its low hardness (5-6) and porous nature, turquoise requires gentle handling. * Cleaning: Use only warm water, a mild soap, and a soft brush. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals, which can damage the stone or its matrix. Dry it thoroughly with a soft cloth. * Wearing: It is best worn as earrings, pendants, or brooches, where it is less likely to be subjected to impact. If worn in a ring, avoid activities that could cause scratches or knocks. The stone can absorb oils and lotions, which may darken its color over time; therefore, it should be put on after applying cosmetics.
Zircon Care
Zircon's hardness of 7.5 makes it relatively scratch-resistant, but its tendency to be brittle requires caution. * Cleaning: Safe to clean with warm soapy water and a soft brush. Avoid sudden temperature changes, as zircon can be sensitive to thermal shock. Ultrasonic cleaners are generally safe, but it's best to consult a jeweler if the stone has inclusions or fractures. * Wearing: Suitable for most jewelry types, but it should be protected from sharp blows. Prong settings are common, but bezel settings can offer additional protection for rings.
Tanzanite Care
Tanzanite's perfect cleavage makes it one of the more delicate birthstones. * Cleaning: Use only warm water, a mild detergent, and a soft brush. Never use an ultrasonic cleaner or steam cleaner, as the vibrations and heat can cause the stone to cleave or fracture. Avoid sudden temperature changes. * Wearing: Due to its perfect cleavage, tanzanite is best suited for earrings, pendants, and brooches. If set in a ring, it should be worn for occasional, low-impact occasions and removed during any manual work or physical activity. A protective setting, such as a bezel or halo, is highly recommended for rings.
Conclusion
The December birthstones—turquoise, zircon, and tanzanite—offer a remarkable diversity within a single month's selection. From the ancient, opaque sky-blue of turquoise, cherished for millennia for its protective qualities, to the brilliant, fire-filled zircon that has served as a diamond alternative, and the modern, color-shifting tanzanite from a single source in Tanzania, each stone tells a unique story. Their differences extend beyond color to their geological origins, gemological properties, and care requirements. While turquoise demands gentle handling due to its softness, zircon offers more durability but can be brittle, and tanzanite requires careful protection due to its perfect cleavage. Understanding these characteristics is essential for anyone looking to purchase or care for jewelry featuring these beautiful gems. Together, they provide a rich and varied palette for December birthdays, ensuring that there is a perfect stone to match every style and preference.