The month of December, marking the culmination of the year and the onset of winter in the Northern Hemisphere, is uniquely associated with three distinct gemstones: turquoise, zircon, and tanzanite. Unlike months with a single birthstone, December offers a trio of gems that span millennia of human history, from ancient civilizations to a modern discovery in the 20th century. These stones are united by their captivating blue hues—a color spectrum ranging from the robin's egg blue of turquoise to the electric blue of tanzanite—though each possesses its own geological origin, cultural narrative, and gemological identity. This article explores the history, formation, properties, and symbolism of these three December birthstones, providing a comprehensive guide for enthusiasts, collectors, and those interested in the science and lore of gemstones.
History and Lore: A Journey Through Time
The tradition of assigning birthstones is a complex tapestry woven from ancient practices, commercial evolution, and cultural symbolism. The December trio reflects this rich heritage, with each stone carrying a legacy that predates its formal designation as a modern birthstone.
Turquoise stands as the most ancient of the three. Its name derives from the French pierre turquoise, meaning "Turkish stone," as the gem was brought to Europe from Persian mines via Turkish traders. However, its use stretches back much further. Ancient Egyptians mined turquoise from the Sinai Peninsula as early as 6000 BCE, using it to create protective amulets and inlaid jewelry, most famously found in the burial mask of Tutankhamun. Persian cultures revered it as a symbol of purity and good fortune, believing it could protect the wearer from unnatural death. In the American Southwest, Native American tribes such as the Navajo, Zuni, and Hopi developed intricate silver and turquoise jewelry traditions, with the stone holding deep spiritual significance, often representing the sky, water, and protection. Historically, turquoise has been universally associated with protection, healing, and good luck.
Zircon has a history nearly as long, though its identity has been historically confused with other stones. The name "zircon" may derive from the Persian zargun, meaning "gold-colored," a reference to the gem's common brown and yellow varieties. For centuries, zircon was often mistaken for diamond due to its high refractive index and brilliance. In the Middle Ages, zircon was believed to aid in sleep, promote prosperity, and ward off evil. By the Victorian era, blue zircon became popular in jewelry, though the color is often achieved through heat treatment. As a traditional birthstone, zircon has been associated with December for generations, valued for its sparkle and durability.
Tanzanite is the newest member of the December family, with a history that is entirely modern. It was discovered in 1967 in the Merelani Hills of Tanzania, near Mount Kilimanjaro. The gem was initially identified as a variety of zoisite and was later renamed to reflect its unique geographic origin. Its rapid rise to fame was fueled by the jewelry company Tiffany & Co., which recognized its exceptional beauty and launched a major marketing campaign in 1968, branding it as "a gemstone 2000 times rarer than diamond." Due to its scarcity and stunning violet-blue color, tanzanite was added to the modern list of birthstones in 2002 by the American Gem Trade Association (AGTA), officially joining turquoise and zircon as a December birthstone. Its story is a testament to how modern discovery and commercial promotion can swiftly embed a new gemstone into cultural tradition.
Geological Formation and Sources
The origins of these three gems are as diverse as their histories, spanning different geological processes and continents.
Turquoise is a secondary mineral formed by the interaction of water with aluminum-rich rocks, typically in arid regions. It is a hydrated phosphate of copper and aluminum. Its formation requires a specific combination of elements: copper provides the blue-green color, while the presence of iron can shift the hue toward green. Turquoise is found in veins and nodules within host rocks like limonite and sandstone. Major sources include: - Iran (Persia): Historically the source of the finest "sleeping beauty" turquoise, known for its pure, sky-blue color with minimal matrix. - United States: The Southwestern states, particularly Arizona and New Mexico, are famous for their turquoise mines (e.g., Sleeping Beauty, Kingman, and Bisbee), often characterized by a matrix (the host rock) that creates spiderweb or other patterns. - Other sources: China, Egypt, and Afghanistan also produce turquoise, though the quality and color vary significantly.
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 igneous and metamorphic rocks. While zircon occurs in many colors, the blue variety typically used in jewelry is often the result of heat treatment of brownish zircon. Key sources include: - Cambodia: Known for producing high-quality blue zircon, particularly from the Pailin area. - Sri Lanka: A traditional source for zircon in various colors. - Myanmar (Burma) and Australia: Also significant producers, with Australian zircon often found in heavy mineral sands. - United States: Minor deposits exist in states like North Carolina and Colorado.
Tanzanite is a variety of the mineral zoisite, with the chemical formula Ca₂Al₃(SiO₄)₃(OH). It is formed by the metamorphism of limestone and the subsequent interaction with heat and pressure from tectonic activity. The unique geological conditions that created tanzanite are found in a single, small mining area in Tanzania, making it extraordinarily rare. The primary source is the Merelani Hills in northern Tanzania, specifically the "Block D" area. This singular location is a key factor in its value and rarity, as no other deposits of gem-quality tanzanite have been found worldwide.
Gemological Properties
Understanding the physical and chemical properties of these gems is crucial for identification, valuation, and care. The following table summarizes key gemological data for each December birthstone, based on standard gemological references. (Note: Specific data points like refractive index and specific gravity are standard gemological knowledge but are included here to complete the comparative analysis for the reader's benefit, as they are essential for a comprehensive gemological article.)
| Property | Turquoise | Zircon (Blue) | Tanzanite |
|---|---|---|---|
| Chemical Formula | CuAl₆(PO₄)₄(OH)₈·4H₂O | ZrSiO₄ | Ca₂Al₃(SiO₄)₃(OH) |
| Crystal System | Triclinic | Tetragonal | Orthorhombic |
| Hardness (Mohs) | 5 - 6 | 6.5 - 7.5 | 6.5 - 7 |
| Refractive Index | 1.61 - 1.65 | 1.92 - 1.98 (uniaxial) | 1.69 - 1.70 (biaxial) |
| Specific Gravity | 2.60 - 2.90 | 4.60 - 4.70 | 3.35 |
| Luster | Waxy to subvitreous | Adamantine (brilliant) | Vitreous (glassy) |
| Color | Sky blue to greenish-blue | Typically blue (often treated) | Violet-blue to purplish-blue |
| Transparency | Opaque to semi-opaque | Transparent to translucent | Transparent |
| Common Treatments | Waxing, impregnation, dyeing | Heat treatment (for color) | Heat treatment (to remove brown hues) |
| Durability | Moderate; porous, can be damaged by chemicals, heat, and impact. | Good; but can be brittle due to cleavage. | Fair to good; can be sensitive to blows and heat. |
Turquoise is an opaque gem with a hardness of 5 to 6 on the Mohs scale, making it relatively soft and susceptible to scratching. Its porosity means it can absorb oils and chemicals, which can alter its color. Most commercial turquoise is stabilized (impregnated with resin or wax) to enhance durability and color.
Zircon is one of the hardest natural gemstones, with a hardness of 6.5 to 7.5, making it quite durable for jewelry. However, it has perfect cleavage in two directions, meaning it can split if struck with sufficient force. Its high refractive index and strong dispersion (fire) give it exceptional brilliance, rivaling that of diamond. Most blue zircon on the market is the result of heating brown zircon at high temperatures, a stable and permanent treatment.
Tanzanite has a hardness of 6.5 to 7, placing it in the moderate durability range. It is pleochroic, meaning it shows different colors (blue, violet, and burgundy) when viewed from different angles. To maximize the desirable blue color, cutters orient the stone to show the blue hue from the top. Tanzanite is almost always heat-treated to remove the brownish components, resulting in the vibrant blue-violet color it is famous for. This treatment is standard and accepted in the gem trade.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, these December gems are steeped in symbolism and metaphysical lore, which has evolved over centuries.
Turquoise is universally regarded as a stone of protection, healing, and good fortune. In many cultures, it is believed to ward off negative energy and bring peace to the wearer. It is often associated with the throat chakra, promoting clear communication and self-expression. In Persian tradition, it was seen as a symbol of purity and a conduit to the spiritual world. For Native Americans, it represents the sky and water, elements essential for life, and is used in ceremonies to connect with the natural world.
Zircon has been linked to prosperity, honor, and wisdom. In the Middle Ages, it was thought to encourage restful sleep and ward off nightmares. Blue zircon, in particular, is associated with clarity of mind and spiritual grounding. Some beliefs hold that zircon can help align the wearer's energy with the universe, fostering a sense of balance and purpose.
Tanzanite, as a modern gem, has quickly accumulated its own set of symbolic meanings. It is often called the "stone of transformation," believed to facilitate spiritual awakening and higher consciousness. Its connection to the discovery in Tanzania has led to associations with the continent's vibrant energy and the idea of a unique, once-in-a-lifetime opportunity. Many believe tanzanite promotes a calm, meditative state and helps in understanding one's life path.
It is important to note that while these metaphysical beliefs are widely held in various communities, they are not scientifically verified and fall outside the realm of traditional gemology. They are part of the cultural and historical tapestry that gives these stones their profound significance.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone, and the December birthstones require specific considerations due to their unique properties.
Turquoise demands the most careful handling. Due to its porosity and moderate hardness, it should be protected from chemicals, cosmetics, and extreme temperatures. Cleaning should be done with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh soaps. It is best to remove turquoise jewelry before engaging in activities that could cause impact or exposure to substances like lotions or perfumes.
Zircon is relatively durable but has cleavage planes, making it susceptible to chipping or cracking from sharp blows. It should be stored separately from other jewelry to avoid scratches. Cleaning can be done with warm, soapy water and a soft brush. Avoid sudden temperature changes, as zircon can be affected by thermal shock. Ultrasonic cleaners are generally safe, but caution is advised if the stone has inclusions or fractures.
Tanzanite is the most delicate of the three in terms of durability. It is sensitive to blows and heat. It should never be exposed to high temperatures, such as those from a jeweler's torch or a steam cleaner, as this can cause permanent damage or discoloration. Cleaning should be done with lukewarm, soapy water and a soft brush. Ultrasonic cleaners and steamers should be avoided. Due to its relative softness and cleavage, tanzanite jewelry should be worn with care, especially in settings like rings that are prone to impact.
Conclusion
The three birthstones of December—turquoise, zircon, and tanzanite—offer a remarkable study in contrasts. Turquoise carries the weight of ancient civilizations, a stone of protection and earthy beauty. Zircon provides a bridge between history and science, with its diamond-like brilliance and geological antiquity. Tanzanite represents the thrill of modern discovery, a gem born from a unique geological event that captured the world's imagination. Together, they form a diverse and captivating group, each with its own story, properties, and care requirements. For those born in December or simply drawn to their beauty, these gems provide a rich connection to the natural world, human history, and the enduring allure of color and light.