December is a month uniquely distinguished in the gemological calendar, offering not one, not two, but three (and in some traditions, four) official birthstones. This multiplicity is not a recent marketing anomaly but a reflection of an evolving tradition, shaped by centuries of cultural exchange, commercial influence, and geological discovery. The stones—turquoise, zircon, and tanzanite—each embody distinct narratives, from ancient protective amulets to modern geological marvels. This article provides a detailed exploration of these gems, tracing their historical journey, geological origins, gemological properties, and enduring symbolism, drawing exclusively from authoritative sources to present a comprehensive guide for enthusiasts, collectors, and students of gemology.
The Evolution of December's Birthstone List
The concept of birthstones is believed to have roots in the Biblical Book of Exodus, where Aaron’s breastplate was adorned with twelve stones representing the twelve tribes of Israel. Over time, these stones were associated with the months of the year, a tradition adopted and adapted by various cultures. For December, the earliest references pointed to ruby as the birthstone. However, the modern list has undergone significant transformation, particularly in the 19th and 20th centuries, reflecting both the influence of the jewelry trade and the discovery of new gem sources.
The documented evolution of the December birthstone list is as follows: * 1870: Turquoise was designated as a December birthstone in a pamphlet by Tiffany & Co. titled Gregorian Birthstone Poems. * 1912: The National Association of Jewellers (now the Jewellers of America) listed turquoise as the primary December birthstone and lapis lazuli as an alternative. * 1952: The Jewelry Industry Council of America added zircon to the list, replacing lapis lazuli. * 2002: Tanzanite was officially recognized as a December birthstone by the American Gem Trade Association (AGTA).
This fluidity underscores the dynamic nature of birthstone traditions, where commercial popularity and cultural trends continually shape the canon. While some sources cite four stones—adding blue topaz to the triad—the most widely accepted modern list by authoritative gemological organizations comprises turquoise, zircon, and tanzanite.
Turquoise: The Ancient Protector
History and Lore
Turquoise is the oldest and most traditional December birthstone, treasured for thousands of years. Evidence of its use dates back to 5,000 BCE in ancient Egypt, where it was employed in jewelry and amulets. Egyptian pharaohs wore turquoise to signify power and a connection to the heavens, believing the stone offered divine protection. In ancient Persia, turquoise was considered a protective charm, warding off the "evil eye" and symbolizing purity and victory. It was also highly valued in China, where it was carved into intricate objects for ceremonial use.
The stone’s journey to becoming a December birthstone is a direct result of 19th-century commercial influence. Its designation by Tiffany & Co. in 1870 helped cement its place in the Western tradition, a position it has held ever since. Across cultures, from Native American tribes to ancient civilizations, turquoise has been consistently associated with protection, good health, and fortune.
Geological Formation and Sources
Turquoise is a phosphate mineral, hydrated copper and aluminum phosphate. It forms in arid regions where acidic, copper-rich groundwater interacts with minerals containing aluminum and phosphorus over millions of years. This process occurs primarily in areas with specific weather conditions that facilitate its formation.
The most significant sources include: * The Southwestern United States: Particularly Arizona and New Mexico, home to famous mines like the Sleeping Beauty Mine. * Iran: Historically the source of the most prized "Persian turquoise," known for its vivid, evenly saturated sky-blue color. * Egypt * China * Mexico * Parts of Central Asia and Africa
The stone often features a characteristic "matrix"—dark veining of host rock embedded within the turquoise. The absence or minimal presence of matrix is highly prized, as seen in varieties like Persian turquoise and Sleeping Beauty turquoise. The Sleeping Beauty Mine in Arizona, before its closure, produced a renowned pure, robin’s-egg blue turquoise with exceptionally low matrix.
Gemological Properties
Turquoise is valued for its distinctive color, ranging from sky blue to green, often influenced by its copper and iron content. It can be semi-transparent to opaque. Its appearance is frequently enhanced by stabilization (impregnation with a clear resin) to improve durability and color consistency.
| Property | Description |
|---|---|
| Color | Sky blue to green; often with dark matrix veining. |
| Hardness | Approximately 5 to 6 on the Mohs scale, making it relatively soft and susceptible to scratching. |
| Transparency | Opaque to semi-transparent. |
| Chemical Formula | CuAl₆(PO₄)₄(OH)₈·4H₂O (hydrated copper aluminum phosphate). |
| Crystal System | Triclinic. |
Due to its hardness and potential for porosity, turquoise requires careful handling. It is sensitive to chemicals, heat, and prolonged exposure to sunlight, which can cause discoloration.
Symbolism and Metaphysical Beliefs
For millennia, turquoise has been a symbol of protection, prosperity, and good fortune. It is believed to soothe anger, promote communication, and bring wisdom, tranquility, and friendship to the wearer. In metaphysical traditions, it is considered a grounding stone that connects the spiritual and physical worlds.
Care and Cleaning
Turquoise jewelry should be handled with care. Clean it only with a soft, damp cloth and mild soap. Avoid ultrasonic cleaners, steam, and harsh chemicals. Store it separately from other jewelry to prevent scratching. Due to its relative softness, it is best suited for pieces that are not subjected to daily wear and tear, such as pendants and earrings, rather than rings.
Zircon: The Ancient Sparkler
History and Lore
Zircon is one of the oldest minerals on Earth, with zircon crystals dating back billions of years found in Australia. As a gemstone, it has been admired for centuries for its brilliant fire and dispersion, often compared to that of diamond. Historically, it was believed to promote prosperity and honor, and was used as a protective talisman during travel.
Its journey to the December birthstone list began in 1952 when the Jewelry Industry Council of America added it to the list, replacing lapis lazuli. The blue variety, in particular, gained prominence as a December stone, offering a brilliant alternative to the softer turquoise. While it comes in a variety of colors, including yellow, green, and red, it is the blue zircon that is most associated with December.
Geological Formation and Sources
Zircon is a zirconium silicate mineral (ZrSiO₄) that forms in igneous and metamorphic rocks. It is a common accessory mineral found in many rock types. The gem-quality blue zircon is typically produced by heating brown zircon crystals to high temperatures (over 1000°C), which changes their color to a vibrant blue. This treatment is permanent and is a standard industry practice.
Major sources of zircon include: * Australia: Particularly from New South Wales, known for producing some of the oldest zircon crystals. * Cambodia * Sri Lanka * Tanzania * United States (specifically in certain pegmatites and placer deposits)
Gemological Properties
Zircon is prized for its exceptional brilliance and fire. It has a high refractive index and strong dispersion, giving it a sparkling quality that can rival diamond. It is also relatively hard, making it suitable for jewelry.
| Property | Description |
|---|---|
| Color | Most commonly blue (from heat treatment), but also yellow, green, brown, and red. |
| Hardness | 6.5 to 7.5 on the Mohs scale, making it durable for jewelry. |
| Refractive Index | 1.92 to 2.01 (high brilliance). |
| Dispersion | 0.039 (high fire, comparable to diamond). |
| Chemical Formula | ZrSiO₄ (zirconium silicate). |
| Crystal System | Tetragonal. |
Zircon is distinct from synthetic cubic zirconia (CZ), a common diamond simulant. Natural zircon is a valuable gemstone in its own right.
Symbolism and Metaphysical Beliefs
Zircon is associated with wisdom, honor, and purity. It is believed to aid in spiritual grounding, promote restful sleep, and bring prosperity. In some traditions, it is thought to alleviate pain and support the immune system.
Care and Cleaning
Zircon is relatively hard but can be brittle due to its crystal structure. It is susceptible to chipping if struck. It is also sensitive to heat, so it should not be subjected to high temperatures during jewelry repair or cleaning. Clean zircon with warm water, mild soap, and a soft brush. Avoid ultrasonic cleaners and sudden temperature changes.
Tanzanite: The Modern Marvel
History and Lore
Tanzanite is the youngest of the December birthstones, a 20th-century discovery that quickly captured the imagination of the gem world. First identified in the 1960s in the Merelani Hills of Tanzania, it was initially mistaken for sapphire. Its unique blue-violet color and rapid rise to fame led to its official recognition as a December birthstone by the American Gem Trade Association (AGTA) in 2002.
Tanzanite’s lore is modern, often linked to its origin story. It is sometimes called the "stone of transformation," believed to facilitate a higher consciousness and spiritual awakening. Its association with December is a testament to the evolving nature of birthstone traditions, embracing a gem that is geologically unique and commercially significant.
Geological Formation and Sources
Tanzanite is a variety of the mineral zoisite, colored by trace amounts of vanadium. It forms under specific geological conditions found only in one location on Earth: the Merelani Hills near Mount Kilimanjaro in Tanzania. This extremely limited geographic source contributes to its rarity and value.
The formation process involves the metamorphism of calcareous rocks under high temperatures and pressures, which allowed vanadium to incorporate into the zoisite crystal structure, creating its signature blue-violet hue.
Gemological Properties
Tanzanite is known for its striking trichroism—the ability to show three different colors (blue, violet, and burgundy) when viewed from different crystal directions. This property is a key identifier and a source of its visual appeal.
| Property | Description |
|---|---|
| Color | Blue-violet; exhibits trichroism (blue, violet, burgundy). |
| Hardness | 6 to 7 on the Mohs scale, moderately hard but softer than quartz. |
| Transparency | Transparent to translucent. |
| Refractive Index | 1.69 to 1.70. |
| Chemical Formula | Ca₂Al₃(SiO₄)₃(OH) (a calcium aluminum silicate hydroxide). |
| Crystal System | Orthorhombic. |
Most tanzanite on the market is heat-treated to enhance its blue color and reduce violet/brown tones. This treatment is stable and widely accepted.
Symbolism and Metaphysical Beliefs
Tanzanite is associated with spiritual growth, intuition, and calmness. It is believed to promote a sense of peace and to facilitate communication between the heart and mind. As a relatively new gem, its metaphysical attributes are largely drawn from modern crystal healing practices.
Care and Cleaning
Tanzanite requires careful handling due to its relative softness and potential for cleavage. It should not be subjected to ultrasonic cleaning or steam. Clean with warm water, mild soap, and a soft brush. It is advisable to remove tanzanite jewelry before physical activities to avoid impacts. Due to its color origin, prolonged exposure to intense heat or light could potentially affect its color, though this is rare with normal wear.
Comparative Overview and Modern Relevance
The three December birthstones offer a spectrum of choices for collectors and jewelry buyers. Turquoise provides an opaque, earthy option with ancient roots. Zircon offers brilliant sparkle and durability. Tanzanite presents a unique, modern color with a singular geographic origin.
The choice often comes down to personal preference, budget, and intended use. Turquoise is generally the most affordable but requires the most care. Zircon offers a diamond-like brilliance at a more accessible price point. Tanzanite, being rarer, commands a higher price but offers a color found in no other natural gemstone.
In terms of care, a hierarchy of durability emerges: zircon is the most durable (Mohs 6.5-7.5), followed by tanzanite (Mohs 6-7), with turquoise being the softest (Mohs 5-6). This practical consideration is crucial for selecting jewelry for daily wear versus occasional use.
Conclusion
The December birthstones—turquoise, zircon, and tanzanite—collectively represent a fascinating intersection of history, geology, and culture. From the ancient protective amulets of Egypt and Persia to the brilliant sparkle of heat-treated zircon and the modern marvel from Tanzania, each gemstone tells a unique story. Their inclusion in the December list reflects the living tradition of birthstones, which adapts to incorporate new discoveries while honoring centuries of lore. For those born in December, the choice is rich and varied, offering not just a gemstone, but a piece of Earth’s history and human culture.