The final month of the year is uniquely represented by three distinct and captivating gemstones: turquoise, tanzanite, and zircon. This trio offers a remarkable spectrum of color, from the opaque, sky-blue of ancient turquoise to the vivid violet-blue of tanzanite and the fiery brilliance of zircon. As December's birthstones, these gems hold deep historical significance, unique geological origins, and specific gemological properties that appeal to collectors, jewelers, and enthusiasts alike. This article explores the history, formation, characteristics, and care of these three remarkable stones, providing a detailed overview for those born in December or anyone captivated by their beauty.
History and Lore
The historical journey of December's birthstones is as varied as their colors. Turquoise is one of the oldest gemstones known to humanity, with evidence of its use dating back thousands of years. Its name is derived from the French term "pierre tourqueise," meaning "Turkish stone," reflecting the historical trade routes through which it reached Europe. Ancient civilizations, including the Egyptians, Persians, and Native Americans, revered turquoise for its protective qualities and vibrant hue. It was often used in jewelry, ceremonial objects, and amulets, believed to ward off evil and bring good fortune. In many cultures, turquoise was also thought to change color to warn its wearer of impending danger or illness, a belief that added to its mystique.
The journey to its modern status as a birthstone is well-documented. The tradition of assigning specific gems to each month has evolved over centuries, but the modern list was largely standardized in 1912 by the American National Association of Jewelers. Turquoise was included in this original list, solidifying its place as a December birthstone. Its inclusion was a nod to its enduring popularity and deep-rooted cultural significance, particularly in Western jewelry traditions.
Zircon, the third of December's birthstones, has a history intertwined with both admiration and confusion. For centuries, it was confused with lower-quality diamonds due to its high refractive index and brilliant sparkle. The term "zircon" is believed to have originated from the Persian word "zargun," meaning "gold-colored," which speaks to its common yellow and brown varieties. However, the most prized color, a vibrant blue, was historically achieved through heat treatment. Blue zircon was particularly popular during the Victorian era, where it was set in jewelry alongside diamonds. Its status as a birthstone was also formalized in the 1912 list, though it has seen periods of fluctuating popularity. Zircon is not to be confused with cubic zirconia, a synthetic diamond simulant, which is a common point of confusion but highlights the natural gem's historical value.
Tanzanite is the newest addition to the December birthstone family, with its discovery and rise to prominence occurring in the 20th century. Unlike turquoise and zircon, its history is not ancient but is instead a modern gemological story. Its discovery in 1967 in the Merelani Hills of Tanzania immediately captured the attention of the gem world due to its unique and intense violet-blue color. The Tiffany & Co. gemological director, Henry Platt, recognized its potential and launched a major marketing campaign in 1968, promoting it as a "gemstone of a lifetime." This strategic introduction helped establish tanzanite as a desirable and exclusive gem. In 2002, the American Gem Trade Association (AGTA) officially added tanzanite as a birthstone for December, providing a modern alternative to the traditional stones. This addition reflects the evolving nature of birthstone traditions and the gemological community's embrace of new discoveries.
Geological Formation and Sources
The origins of these three gems are as diverse as their histories, each forming under distinct geological conditions and found in specific regions of the world.
Turquoise is a secondary mineral, meaning it forms through the alteration of pre-existing rocks. It is a hydrated phosphate of copper and aluminum, and its formation requires the presence of both copper (which provides the blue color) and aluminum in a low-temperature, arid environment. Typically, turquoise forms in the near-surface weathering zones of copper deposits, where acidic, copper-rich waters react with aluminous rocks like limestone or volcanic ash. This process can take millions of years. The most significant sources of turquoise include the southwestern United States (particularly Arizona, New Mexico, and Nevada), Iran (which produces the prized "Persian turquoise"), and China. The quality of turquoise is often judged by its color, matrix (the host rock that remains within the gem), and stability. Some turquoise is "stabilized" with resins to enhance its durability and color, a common practice in the industry.
Zircon is a zirconium silicate mineral (ZrSiO₄) that forms in igneous and metamorphic rocks. It is one of the oldest minerals on Earth, with crystals found in zircon grains from Western Australia dating back over 4 billion years. Zircon forms during the crystallization of magma, particularly in granitic pegmatites and certain types of volcanic rocks. It is a common accessory mineral in many igneous rocks and is highly resistant to weathering, which is why it is often found in sedimentary deposits as well. The gem-quality zircon used in jewelry is mined from various locations worldwide. The primary sources include Cambodia (notably for blue zircon), Sri Lanka (which produces a variety of colors, including brown, yellow, and green), Thailand, Myanmar, and Australia. The intense blue color most associated with gem zircon is typically the result of heat treatment of brownish zircon crystals, a process that is stable and widely accepted in the gem trade.
Tanzanite is a variety of the mineral zoisite (a calcium aluminum silicate). Its formation is uniquely tied to a specific geological event. Tanzanite is found exclusively in a small, four-square-kilometer mining area in the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. The gem forms through the metamorphism of aluminum-rich rocks (such as gneiss) that were subjected to intense heat and pressure during the formation of the East African Rift. This process introduced vanadium, which is responsible for tanzanite's signature blue-violet color. The scarcity of this specific geological formation makes tanzanite one of the rarest gemstones in the world. Mining is conducted in four zones (A, B, C, and D) within the Merelani Hills, with Zone C being the most productive. The limited geographic origin of tanzanite contributes significantly to its value and allure.
Gemological Properties
Understanding the physical and chemical properties of these gems is essential for their identification, valuation, and care. The following table summarizes key gemological characteristics for turquoise, tanzanite, and zircon.
| Gemstone | Chemical Formula | Crystal System | Mohs Hardness | Refractive Index | Specific Gravity | Common Treatments | Notable Properties |
|---|---|---|---|---|---|---|---|
| Turquoise | CuAl₆(PO₄)₄(OH)₈·4H₂O | Triclinic | 5 - 6 | 1.61 - 1.65 | 2.6 - 2.9 | Stabilization (resin), dyeing | Opaque, often porous, can be stabilized for durability. |
| Tanzanite | Ca₂Al₃(SiO₄)₃(OH) | Orthorhombic | 6.5 - 7 | 1.69 - 1.70 | 3.35 | Heat treatment (standard) | Pleochroic (shows blue, violet, and burgundy), trichroic. |
| Zircon | ZrSiO₄ | Tetragonal | 6.5 - 7.5 | 1.92 - 2.01 | 4.6 - 4.7 | Heat treatment (for blue color) | High refractive index and dispersion ("fire"), can be radioactive. |
Turquoise is an opaque gem, meaning light does not pass through it. Its hardness on the Mohs scale is relatively low (5-6), making it softer and more porous than many other gems. This porosity means it can absorb oils, chemicals, and even water, which can affect its color and stability over time. The chemical formula indicates its composition as a hydrated phosphate of copper and aluminum. Its specific gravity is variable due to the presence of matrix and porosity. Many turquoise stones on the market are stabilized, a process where the porous stone is impregnated with a clear resin or wax to increase durability and prevent color change. This treatment is standard and should be disclosed by reputable sellers.
Tanzanite is a transparent to translucent gemstone with a hardness of 6.5 to 7 on the Mohs scale, making it suitable for jewelry but requiring some care to avoid scratching. Its most defining gemological property is its strong pleochroism—the ability to display different colors when viewed from different crystal directions. Tanzanite exhibits trichroism, typically showing blue, violet, and reddish-brown or burgundy colors. The primary color seen in gemstones is a result of heat treatment, which is a standard and stable industry practice to remove the brownish component and enhance the violet-blue hue. The chemical formula confirms it as a variety of zoisite, with vanadium as the trace element responsible for its color.
Zircon is a transparent gemstone known for its exceptional brilliance and fire, which rivals that of diamond. It has a high refractive index (1.92-2.01) and strong dispersion (0.039), contributing to its dazzling sparkle. Its hardness ranges from 6.5 to 7.5, making it durable enough for most jewelry settings, though it can be brittle due to its tetragonal crystal structure and perfect cleavage in one direction. The chemical formula is simple: zirconium silicate (ZrSiO₄). Blue zircon, the most popular color for jewelry, is almost always the result of heating brown zircon crystals. This treatment is permanent and widely accepted. It is important to note that some zircon crystals can be mildly radioactive due to the presence of uranium and thorium impurities, but this radioactivity is negligible and poses no health risk in jewelry.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, all three December birthstones are steeped in symbolism and metaphysical lore, which has been passed down through generations.
Turquoise has long been associated with protection, wisdom, and good fortune. In many Native American cultures, it is considered a sacred stone, representing life, health, and the sky. It was often used in ceremonial objects and jewelry to connect the wearer with the spiritual world. In ancient Persia, turquoise was believed to ward off the "evil eye" and was worn as a protective amulet. The belief that turquoise changes color to warn of danger or illness is a persistent part of its lore, though it is more likely due to its porosity and reaction to the wearer's body chemistry and environmental conditions. Today, it is often seen as a stone of calm, balance, and emotional stability.
Tanzanite, as a modern gem, carries symbolism linked to its origin and unique color. It is often associated with transformation, new beginnings, and spiritual awakening. Its intense violet-blue color is said to stimulate the higher chakras, promoting intuition and a deeper connection to the divine. Because it is found in only one location on Earth, it is also considered a symbol of uniqueness and preciousness. Some metaphysical beliefs attribute tanzanite with the ability to alleviate stress and anxiety, fostering a sense of peace and clarity.
Zircon has a more complex symbolic history due to its confusion with diamond. Historically, it was believed to promote honor, purity, and wisdom. The blue variety, in particular, was associated with tranquility and peace. In some traditions, zircon was thought to aid in sleep and ward off nightmares. Its brilliant sparkle led to associations with light and enlightenment. In modern crystal healing, zircon is sometimes used to boost self-esteem and alleviate feelings of inadequacy. The stone's association with the 4th wedding anniversary also ties it to themes of enduring love and commitment.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of these gemstones, with each requiring specific handling due to their distinct properties.
Turquoise, with its low hardness and porosity, is the most delicate of the three. It should be protected from harsh chemicals, including cosmetics, perfumes, and household cleaners, which can damage or discolor the stone. Cleaning should be done with a soft, dry cloth. If necessary, a mild soap and lukewarm water solution can be used, but the stone must be dried immediately and thoroughly. Avoid ultrasonic and steam cleaners, as they can cause cracking or discoloration. Stabilized turquoise is more durable but should still be treated with care. It is best to store turquoise jewelry separately to prevent scratching by harder gems.
Tanzanite requires careful handling due to its good cleavage (a tendency to break along flat planes). It is susceptible to damage from sharp blows and should be removed during physical activities or heavy manual work. Cleaning tanzanite is relatively straightforward: use warm, soapy water and a soft brush, then rinse and dry thoroughly. Ultrasonic cleaners and steam cleaning are not recommended, as the vibrations and heat can potentially cause damage, especially if the stone has any inclusions or fractures. Given its hardness of 6.5-7, it is suitable for rings but may be better placed in earrings or pendants where it is less likely to receive impacts.
Zircon is relatively durable due to its hardness, but it has perfect cleavage in one direction, making it susceptible to chipping or cracking if struck with force. It is also sensitive to rapid temperature changes, which can cause internal stress. For cleaning, use warm, soapy water and a soft brush. Avoid ultrasonic cleaners and steam cleaning, as the vibrations and heat can exacerbate any existing cleavages or inclusions. Zircon should be stored carefully, ideally in a soft cloth pouch or a separate compartment in a jewelry box, to prevent scratching harder stones and to avoid damage from impacts.
Conclusion
The December birthstones—turquoise, tanzanite, and zircon—offer a remarkable diversity that reflects the richness of the natural world. Turquoise carries the weight of ancient history and protective symbolism, with its opaque, sky-blue color evoking the skies and waters of our planet. Tanzanite represents the pinnacle of modern gemology, a rare and beautiful stone born from a unique geological event, captivating with its trichroic brilliance. Zircon, with its fiery sparkle and ancient origins, bridges the gap between the past and present, its brilliant fire often mistaken for diamond. Together, they provide a stunning array of options for those born in December, each with its own story, scientific properties, and care requirements. Understanding the history, formation, and characteristics of these gems deepens the appreciation for their enduring beauty and significance.