The calendar birthstone for December 24th is a gemstone that stands apart in the mineral kingdom due to its singular geographic origin and its relatively recent introduction to the global market. Tanzanite, a blue to violet variety of the mineral zoisite, is the primary birthstone associated with this date. While some traditional lists may include turquoise or zircon as alternative December stones, sources identify Tanzanite as the distinct and most widely recognized gem for those born on this day.
First unearthed in the foothills of Mount Kilimanjaro in Tanzania in 1967, this gemstone possesses a color spectrum that ranges from deep indigo to pale lavender, a phenomenon driven by its unique geological formation. Its rapid ascent from a local curiosity to a globally cherished jewel was fueled by a strategic marketing campaign and its inherent rarity. As a gemstone that is found in only one location on Earth, it represents not only a personal birthright but also a geological anomaly.
This article explores the comprehensive profile of Tanzanite, detailing its geological formation and exclusive mining locations, the specific gemological properties that define its value, the historical journey that transformed it into a modern birthstone, and the metaphysical beliefs that surround it. Furthermore, it provides essential guidelines for the care and maintenance of this captivating, yet somewhat delicate, jewel.
History and Lore
The history of Tanzanite is a narrative of modern discovery, distinct from the ancient lineages of gems like diamond or ruby. The gemstone’s journey began in 1967, when it was first identified by a Tanzanian miner in the Merelani Hills of northern Tanzania. Prior to the discovery of this blue variety, zoisite had been known to mineralogists for over a century, existing primarily in colors such as green, pink, and brown. However, the blue to violet hue found in Tanzania was unprecedented in the mineral’s history.
The catalyst for the gemstone’s global fame occurred shortly after its discovery. In 1968, the luxury jewelry retailer Tiffany & Co. recognized the potential of this vividly colored stone. The company launched a major advertising campaign, promoting Tanzanite as the "gemstone of a generation" and establishing it as the featured birthstone for December. This marketing effort was highly successful, propelling Tanzanite from an obscure mineral to a sensation in the jewelry world almost overnight.
The gemstone’s nomenclature pays homage to its origin; it was named Tanzanite by Tiffany & Co. to reflect its exclusive geographic source within Tanzania. This naming convention underscored the stone's rarity, a marketing point that remains valid today. Over the decades, Tanzanite has solidified its status not only as a birthstone but also as a significant anniversary gift. It is currently recognized as the gemstone for the 24th wedding anniversary, adding a layer of matrimonial symbolism to its profile.
Geological Formation and Sources
Tanzanite is a testament to the unique geological conditions found in a specific corner of East Africa. It is a variety of the mineral zoisite, belonging to the epidote group. The gemstone’s formation is the result of a rare combination of geological events that occurred millions of years ago.
The Role of Tectonic Activity
The genesis of Tanzanite is linked to the tectonic activity that shaped the East African Rift Valley. The intense heat and pressure generated by the collision of tectonic plates subjected the zoisite deposits to metamorphic changes. This event occurred during the Precambrian era, roughly 585 million years ago. The specific conditions of this event transformed the original brownish zoisite, infusing it with the trace elements necessary to produce the prized blue and violet colors.
The Merelani Hills: A Singular Source
The geographical exclusivity of Tanzanite is one of its defining characteristics. Commercial mining of Tanzanite is restricted to a very small area in the Merelani Hills of northern Tanzania, located near the base of Mount Kilimanjaro. Sources confirm that this is the only place on Earth where Tanzanite is mined commercially. The landscape of the mining area is described as grass-covered hillsides, scrub brush, and rocky soil, with the snow-capped peaks of Mount Kilimanjaro visible in the distance.
The mining operations in the Merelani Hills range from small-scale, artisanal diggings to major mechanized operations. In the deeper, mechanized mines, workers recover the rough gemstone from shafts dug over 100 meters (more than 300 feet) deep into the earth. The difficulty of access and the limited geographic scope of the deposit contribute significantly to the gem's rarity and value.
The Transformation from Zoisite
It is important to note that the rough material as it comes out of the ground is often not the vibrant blue associated with the finished gem. Most rough Tanzanite begins as brownish zoisite. The distinctive blue to violet hues are typically the result of a controlled heat treatment process. This heating is generally done at relatively low temperatures (around 300 to 400 degrees Celsius) to remove the brownish components and reveal the blue color. This treatment is considered stable and permanent, meaning the color will not fade over time. Unlike some other treated gemstones, the heat treatment of Tanzanite does not introduce additional durability concerns, though the stone itself remains somewhat delicate.
Gemological Properties
Tanzanite is prized for its pleochroism, color saturation, and clarity. Understanding its physical and optical properties is essential for gemologists, jewelers, and collectors.
Color and Pleochroism
The most celebrated property of Tanzanite is its color. The gem exhibits a range of hues from deep ultramarine blue to violet, with the most valuable stones showing a rich, saturated blue with violet undertones. The color is caused by trace amounts of vanadium within the crystal structure. When the vanadium-bearing zoisite is heated, the oxidation state of the vanadium changes, resulting in the absorption of light that produces the blue and violet colors.
Tanzanite is strongly pleochroic. Pleochroism is the optical phenomenon where a gemstone appears to be different colors when viewed from different angles. In the case of Tanzanite, the pleochroism displays three distinct color directions: blue, violet, and burgundy (or reddish-brown). Gem cutters must orient the rough stone carefully to ensure the final gem displays the desirable blue/violet colors, rather than the less attractive brownish hues, when viewed from the top.
Hardness and Durability
On the Mohs scale of hardness, Tanzanite rates between 6 and 7. While this hardness is sufficient for jewelry wear, it indicates that Tanzanite is softer than many other popular gemstones, such as sapphire (9) or diamond (10). Consequently, Tanzanite is prone to scratching and abrasion if handled carelessly. It is not recommended for daily wear items like rings that might receive hard knocks, unless the setting is protective (such as a bezel).
Chemical Composition
Tanzanite is a calcium aluminum hydroxyl silicate mineral (Ca2Al3(SiO4)3(OH)), belonging to the epidote group. The presence of vanadium is the impurity responsible for its blue coloration.
Clarity and Cutting
Tanzanite is typically a "clean" gemstone, meaning it usually has few inclusions. High-quality Tanzanite is often "eye-clean," lacking visible imperfections to the naked eye. This clarity allows for excellent light transmission and brilliance. Because of the strong pleochroism, the cut of the stone is critical. The orientation of the facets must maximize the blue and violet colors while minimizing the visibility of the brownish body color that may be present in the rough.
The following table summarizes the key gemological data for Tanzanite:
| Property | Description |
|---|---|
| Mineral Species | Zoisite |
| Chemical Formula | Ca2Al3(SiO4)3(OH) |
| Color | Blue to Violet; often heat-treated from brown |
| Mohs Hardness | 6 to 7 |
| Crystal System | Orthorhombic |
| Refractive Index | 1.691 – 1.700 |
| Specific Gravity | 3.35 |
| Origin | Merelani Hills, Tanzania |
Symbolism and Metaphysical Beliefs
Tanzanite is surrounded by a rich tapestry of metaphysical beliefs and symbolic meanings, ranging from spiritual insight to physical protection. These beliefs add a layer of intangible value to the gemstone, appealing to those who view jewelry as more than mere adornment.
Spiritual Insight and Intuition
One of the most common metaphysical attributes associated with Tanzanite is the enhancement of spiritual insight. Believers in crystal healing suggest that Tanzanite stimulates the throat chakra and the third eye chakra, facilitating clearer communication and heightened intuition. It is often described as a stone of transformation, helping the wearer navigate changes in their life with greater ease and spiritual understanding.
Calmness and Emotional Balance
The mesmerizing blue-violet hue of Tanzanite is believed to evoke a sense of calmness and tranquility. Many sources suggest that wearing Tanzanite can help soothe an agitated mind, reducing stress and anxiety. It is associated with emotional balance, helping to harmonize conflicting feelings and promoting a state of inner peace. This calming effect is often linked to the stone’s connection to the holiday season, as its colors and perceived energy align with the reflective and peaceful atmosphere of that time of year.
Prosperity and Protection
Historically and culturally, Tanzanite is also associated with good fortune. Some traditions believe that wearing the gemstone can attract prosperity and abundance. Additionally, it is viewed as a protective talisman. Similar to other blue gemstones, it has been believed to ward off negative energies and protect the wearer from harm. In some belief systems, it is said to alert the wearer to danger by changing color, a folklore element that adds to its mystique.
Care and Cleaning
Due to its specific physical properties, Tanzanite requires careful handling and maintenance to preserve its beauty and structural integrity. Understanding its vulnerabilities is crucial for owners of Tanzanite jewelry.
Durability Concerns
The primary concern with Tanzanite is its relative softness (6 to 7 on the Mohs scale). It is susceptible to scratching from everyday objects, including dust (which is often composed of harder minerals like quartz). It can also abrade (wear down) if subjected to friction or rough handling. Therefore, it is highly recommended to store Tanzanite jewelry separately from other jewelry pieces, ideally in a soft cloth pouch or a lined jewelry box compartment.
Heat and Temperature Sensitivity
While the color of Tanzanite is stabilized by heat treatment, the stone itself is sensitive to extreme temperatures. Sudden temperature changes or exposure to very high heat can cause the gemstone to crack or fracture. This makes it dangerous to subject Tanzanite to ultrasonic cleaners or steam cleaners, as the high heat and vibrations can cause damage. Jewelers generally advise against using these methods for Tanzanite.
Chemical Resistance
Tanzanite is susceptible to attack by strong acids, specifically hydrochloric acid and hydrofluoric acid. While these chemicals are not common in daily life, exposure to household cleaners or industrial chemicals can damage the stone. Therefore, it is advisable to remove Tanzanite jewelry before cleaning with harsh chemicals or engaging in activities where chemical exposure is possible.
Recommended Cleaning Methods
The safest way to clean Tanzanite is using warm water, a mild soap (such as dish soap), and a soft brush (like a baby toothbrush). Gently scrub the stone and the setting, rinse thoroughly with clean water, and dry with a soft, lint-free cloth. Because of its potential for cracking, thermal shock should be avoided; do not expose the stone to extreme temperature changes during the cleaning process.
Best Jewelry Settings
Given its durability profile, Tanzanite is best suited for jewelry types that are less prone to impact. Earrings and pendants are ideal choices, as they are located on parts of the body that are less likely to experience knocks or abrasion. While Tanzanite can be set into rings, it should be done with caution. Protective settings, such as bezels, are preferred over prong settings for rings to minimize the risk of damage to the gem’s edges.
Conclusion
Tanzanite remains one of the most significant discoveries in the 20th-century gemstone industry. As the primary birthstone for December 24th, it offers a unique combination of rarity, vivid color, and modern history. Its exclusive origin in the Merelani Hills of Tanzania ensures that it remains a finite resource, adding to its allure for collectors and enthusiasts.
The gemstone’s journey from a brownish zoisite to a brilliant blue-violet jewel is a testament to the transformative power of geological forces and human ingenuity in gem cutting and treatment. While its hardness of 6 to 7 necessitates careful handling and specific settings, its optical beauty—particularly its strong pleochroism—makes it a standout in the world of fine jewelry.
Beyond its physical attributes, Tanzanite carries significant cultural and symbolic weight. It is associated with spiritual awakening, emotional calm, and protection, themes that resonate deeply with those born on December 24th. Whether appreciated for its scientific properties, its historical rise to prominence, or its metaphysical associations, Tanzanite stands as a jewel of enduring fascination and distinctiveness.