For those born in the final month of the year, December offers a unique and diverse selection of birthstones: tanzanite, turquoise, and zircon. Unlike months with a single primary gem, December provides a choice of three distinct stones, each with its own geological story, historical significance, and visual appeal. These gems are celebrated for their captivating shades of blue, from the deep violet-blue of tanzanite to the sky-blue of turquoise and the brilliant fire of blue zircon. This article explores the rich history, formation, gemological properties, and cultural symbolism of each of these remarkable December birthstones, providing a comprehensive guide for enthusiasts, collectors, and anyone captivated by the beauty of these gems.
History and Lore
The history of December's birthstones spans millennia and continents, with each stone carrying its own legacy. Turquoise is one of the oldest known gemstones, with evidence of its use dating back over 2000 years. In the Southwestern United States, Native American cultures were crafting beads, pendants, and inlay work from turquoise long before European contact. This ancient art form remains a vital part of Southwestern culture today. The gem's name itself is derived from the French pierre turquoise, meaning "Turkish stone," as it was first brought to Europe from Persian mines via Turkey.
Zircon has a history intertwined with diamonds. Due to its high luster and brilliant fire, zircon was historically used as a diamond simulant. Its name is likely derived from the Persian zargun, meaning "gold-colored," though the gem occurs in a wide spectrum of hues. The modern tradition of assigning birthstones by month saw a significant update in 1952 when zircon was added to the list of December stones, replacing lapis lazuli. This addition reflected the gem's enduring appeal and its ability to offer a brilliant, affordable alternative to diamonds.
Tanzanite is the newest addition to the December family. It was only discovered in the late 20th century and was formally recognized as a December birthstone in 2002. Its rapid ascent to prominence is a testament to its stunning color and the successful marketing efforts that positioned it as a rare and precious gem. Its introduction expanded the options for December-born individuals, offering a modern gem with a captivating story of discovery.
Geological Formation and Sources
Understanding the origin of these gems highlights their remarkable diversity. Turquoise is a secondary mineral that forms in arid regions where acidic, copper-rich waters percolate through host rocks containing aluminum and phosphorus. It is often found in veins and nodules within the host rock. Major sources for turquoise include the United States (particularly Arizona, New Mexico, and Nevada), Iran, and China. The gem's color and matrix (the host rock it is embedded in) vary significantly depending on the specific mineral composition of its origin.
Zircon is one of the oldest minerals on Earth, found in many igneous, metamorphic, and sedimentary rocks. It forms as crystals during the cooling of magma. The gem-quality zircon used in jewelry comes from a variety of locations, including Cambodia, Sri Lanka, Thailand, Australia, and Nigeria. A significant portion of the blue zircon seen in the market today has been heat-treated to achieve its desirable color, a process that can transform naturally yellow, red, or brown zircon into a vibrant blue.
Tanzanite is found in only one place on Earth: the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. This geographic exclusivity is a key factor in its rarity and value. The gem is a variety of the mineral zoisite and is formed by the metamorphism of aluminous rocks. The intense heat of this process, combined with specific geological conditions, creates the unique blue-to-violet crystals. The limited mining area contributes to the perception that tanzanite is a "one-generation" gemstone, as supplies are finite.
Gemological Properties
Each December birthstone possesses a unique set of gemological characteristics, which influence their durability, appearance, and care requirements.
Tanzanite
Tanzanite is a member of the zoisite group. It is prized for its vivid blue to bluish violet color, which is almost always the result of heat treatment applied to brownish zoisite crystals. This heat treatment is permanent and stable. Tanzanite exhibits strong pleochroism, meaning it shows different colors—typically blue, violet, and reddish-purple—from different viewing angles. This property gives it a dynamic and captivating appearance. On the Mohs scale of hardness, tanzanite ranks between 6 and 7, making it relatively durable but susceptible to scratching by harder materials. It has perfect cleavage in one direction, which means it can split if struck with sufficient force along that plane.
Turquoise
Turquoise is an opaque mineral with a hardness of 5 to 6 on the Mohs scale, making it relatively soft and prone to scratching. Its chemical composition is hydrated copper and aluminum phosphate. The color of turquoise ranges from blue to blue-green to yellowish green, with bright, even blue being the most valued. Turquoise is often found with a matrix, which is the remnants of the host rock it formed within. Because it is opaque, it is typically cut into cabochons (smooth, rounded shapes) rather than faceted. Its durability is suitable for jewelry that is not subjected to daily wear and tear, such as pendants and earrings.
Zircon
Zircon is a zirconium silicate mineral. It is known for its high refractive index and high dispersion, which give it a brilliant luster and fire similar to that of a diamond. Natural zircon commonly occurs in yellow, red, or brown colors, but heat treatment can produce a stable blue color, which is the most popular variety today. Zircon has a hardness of 6.5 to 7.5 on the Mohs scale, making it one of the harder gemstones in this group, but it is brittle and can be prone to chipping due to its perfect cleavage in two directions. Care must be taken during cutting and setting to avoid impact.
Comparative Gemological Properties
| Gemstone | Chemical Composition | Mohs Hardness | Crystal System | Key Distinguishing Features |
|---|---|---|---|---|
| Tanzanite | Ca₂Al₃(SiO₄)₃(OH) | 6 - 7 | Orthorhombic | Strong pleochroism (blue/violet/reddish), often heat-treated from brown. |
| Turquoise | CuAl₆(PO₄)₄(OH)₈·4H₂O | 5 - 6 | Triclinic (massive) | Opaque, blue to green, often with a matrix (host rock). |
| Zircon | ZrSiO₄ | 6.5 - 7.5 | Tetragonal | High luster and fire, often heat-treated to blue, brittle with perfect cleavage. |
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, these gemstones are rich with symbolic meaning and have been attributed with various metaphysical properties throughout history. While these beliefs are not scientifically verified, they form an important part of the cultural heritage of these stones.
Turquoise is widely regarded as a stone of protection, healing, and good fortune. Many cultures, including ancient Egyptian, Persian, and Native American, have viewed turquoise as a sacred stone. It is believed to ward off negative energy and bring peace to the wearer. In some traditions, it is thought to change color to warn of impending danger or illness.
Zircon, often confused with cubic zirconia (a diamond simulant), has a history of being associated with wisdom, honor, and purity. In some beliefs, it is said to aid in sleep, promote prosperity, and stimulate the chakras. Its fiery brilliance has linked it to spiritual energy and clarity of thought.
Tanzanite, as a relatively new gem, lacks the ancient lore of turquoise or zircon. However, it has quickly developed its own symbolism. It is often associated with transformation, intuition, and spiritual awakening. Some believe it can open the mind to new perspectives and enhance communication. Its unique color and rarity contribute to its modern mystique.
Care and Cleaning
Proper care is essential to maintain the beauty and integrity of these birthstones, given their varying levels of hardness and durability.
Tanzanite: Due to its perfect cleavage, tanzanite should be protected from hard blows and rough handling. It is best suited for jewelry that is not worn daily, such as pendants and earrings. Clean tanzanite with warm, soapy water and a soft brush. Avoid ultrasonic and steam cleaners, as the heat and vibrations can cause damage.
Turquoise: As a soft and porous stone, turquoise is susceptible to scratches, chemicals, and temperature changes. It can be damaged by cosmetics, perfumes, and lotions. Clean it gently with a soft, dry cloth. If necessary, use lukewarm water and a mild soap, but dry it thoroughly immediately afterward. Never soak turquoise or use harsh chemicals.
Zircon: While zircon is relatively hard, its perfect cleavage makes it vulnerable to impact. It is not recommended for rings that will be worn daily, especially for people with active lifestyles. Clean zircon with warm, soapy water and a soft brush. Avoid sudden temperature changes, as they can cause fractures in some zircons. Ultrasonic cleaners are generally safe for zircon, but steam cleaning is not recommended.
Conclusion
December's birthstones—tanzanite, turquoise, and zircon—offer a remarkable range of choices, each with its own distinct character. From the ancient, protective lore of turquoise and the diamond-like fire of zircon to the modern, transformative allure of tanzanite, these gems provide a meaningful and beautiful connection for those born in the last month of the year. Their diverse origins, from the arid deserts of the American Southwest to the exclusive mines of Tanzania, and their unique gemological properties make them fascinating subjects of study and cherished additions to any jewelry collection. By understanding their history, science, and care, one can fully appreciate the depth and beauty of these three exceptional December birthstones.