The final month of the year is represented by a unique trio of birthstones: turquoise, zircon, and tanzanite. Each gem offers a distinct shade of the color spectrum, from the opaque, sky-blue turquoise to the brilliant, fiery zircon and the pleochroic, violet-blue tanzanite. These stones have been cherished across millennia, from ancient civilizations to modern jewelry markets, each carrying its own history, geological origin, and cultural significance. For those born in December, this diverse selection provides ample choice, allowing for personal expression through a range of colors, properties, and price points. This article explores the geological formation, gemological properties, historical lore, and care requirements of these three captivating birthstones, drawing exclusively from authoritative gemological sources.
History and Lore
The history of December’s birthstones spans continents and centuries, with each gem telling a different story of human interaction with the natural world.
Turquoise boasts one of the longest histories as a gemstone. Evidence indicates that Native Americans in the southwestern United States were using turquoise over 2,000 years ago, crafting beads, pendants, inlay work, and small sculptures. This deep connection to the stone ensured that turquoise remains an integral part of Southwestern culture to this day. Its journey into the official birthstone list is more recent; it has long been associated with December, and modern charts consistently list it as a primary option.
Zircon has a history intertwined with the allure of diamond. Due to its high luster and ability to produce colorful fire similar to diamond, zircon was historically used as an alternative to the more expensive precious gem. Its status as a December birthstone was solidified in 1952, when it replaced lapis lazuli on most official lists. This change reflected a shift in gem availability and market preferences, positioning zircon as a distinct and valuable gem in its own right.
Tanzanite is the newest addition to the December family. It was formally added by the American Gem Trade Association, marking the first change to the birthstone list in 50 years. This addition highlights the dynamic nature of gemology, where new discoveries can reshape traditional charts. While it lacks the ancient history of turquoise or zircon, its rapid ascent to birthstone status underscores its unique visual appeal and growing popularity in the modern jewelry market.
The evolution of the birthstone chart itself is a relevant backdrop. The National Association of Jewelers (now Jewelers of America) established the first official chart in the United States. Subsequent updates, including the 1952 revision that added zircon and the later addition of tanzanite, demonstrate an ongoing process of standardization that incorporates both tradition and new discoveries.
Geological Formation and Sources
Understanding where these gems come from reveals the fascinating processes that create their unique structures and colors.
Turquoise is a mineral (hydrated phosphate of copper and aluminum) that forms in arid regions where acidic, copper-rich waters percolate through rocks containing aluminum and phosphorus. The southwestern United States is a historically significant source, as evidenced by its ancient use by Native American cultures. While many people can afford genuine turquoise, the market also includes lab-created alternatives, which are available for cost-conscious shoppers. The primary appeal of natural turquoise lies in its opaque nature and characteristic matrix patterns.
Zircon is a mineral with a complex geological history. It is one of the hardest minerals on Earth and is highly resistant to chemical and physical weathering. This durability means that zircon crystals found in sedimentary deposits can be billions of years old, making them some of the oldest materials on the planet. Natural zircons are most commonly found in colors like yellow, red, or brown. The vibrant blue color that constitutes about 80% of the zircons sold today is typically the result of heat treatment applied to these naturally occurring crystals. Major sources for zircon include various global locations, though specific countries are not detailed in the provided materials.
Tanzanite is a variety of the mineral zoisite and owes its existence to a unique geological event. It is found in only one small area of Tanzania, near Mount Kilimanjaro. Its formation is linked to the intense heat and pressure from a massive tectonic event that transformed the original zoisite into the blue-violet variety known as tanzanite. Like zircon, the vivid blue to bluish purple color of most tanzanite sold in jewelry is produced by heat treatment, which enhances or induces the desirable hue.
Gemological Properties
The physical and optical characteristics of these gems dictate their durability, appearance, and how they should be worn and cared for.
Turquoise is an opaque gem, meaning light does not pass through it. Its color ranges from blue to blue-green to yellowish green, with bright blue being the most preferred. Due to its opacity, it is typically cut into cabochon shapes—smooth, rounded domes—often in freeform cuts to maximize the use of the rough material. Its hardness on the Mohs scale is relatively low, making it susceptible to scratching. It also has a low hardness, which means it can be easily scratched in everyday wear.
Zircon is known for its high luster and brilliance. It exhibits a high refractive index, which contributes to its sparkle and its historical use as a diamond simulant. Zircon has a hardness of 6.5 to 7.5 on the Mohs scale, making it relatively durable, though it can be brittle and prone to breakage due to its crystal structure. Its most popular color today is blue, but it can be found in a wide color suite including rose, peach, yellow, green, white, champagne, cognac, and mocha. The white, blue, green, yellow, peach, and rose colors are often produced by heat treatment. Zircon is also noted for its "fire," which is the dispersion of light into spectral colors, similar to diamond.
Tanzanite is prized for its distinctive color-changing property, a phenomenon known as pleochroism. Its color appears to shift from blue to bluish purple to bluish violet depending on the angle of viewing and the light source. This characteristic adds to its allure and complexity. The gem has a hardness of 6.5 to 7 on the Mohs scale, similar to zircon, but it has perfect cleavage in one direction, making it more vulnerable to breaking if struck with force. Most tanzanite sold in jewelry has been heat-treated to achieve its signature blue to bluish violet color.
Summary of Key Gemological Properties
The following table summarizes the primary gemological characteristics of the December birthstones based on the provided sources.
| Gemstone | Typical Color(s) | Hardness (Mohs) | Key Optical Property | Common Cut | Treatment Notes |
|---|---|---|---|---|---|
| Turquoise | Blue, blue-green, yellowish-green | Low (specific value not given) | Opaque | Cabochon (often freeform) | Lab-created versions available |
| Zircon | Blue (most popular), also yellow, red, brown, and treated colors | 6.5 - 7.5 | High luster, high fire (dispersion) | Various, often faceted | ~80% of blue zircons are heat-treated |
| Tanzanite | Blue, bluish purple, bluish violet | 6.5 - 7 | Pleochroism (color change) | Faceted | Most commercial stones are heat-treated |
Symbolism and Metaphysical Beliefs
While the provided sources focus primarily on geological and gemological facts, some information about cultural significance and beliefs can be inferred or is directly stated.
Turquoise has been deeply embedded in the cultural fabric of Southwestern Native American tribes for millennia. Its use in art and jewelry for over 2,000 years suggests it held significant symbolic value, likely related to the sky, water, and protection. The stone’s enduring role in this culture speaks to its profound symbolic importance.
Zircon is historically associated with wisdom, prosperity, and honor. Its use as a diamond alternative likely imbued it with some of the diamond’s traditional symbolism, such as strength and clarity, though the sources do not explicitly state this. Its brilliant fire and luster may have been linked to spiritual light or insight.
Tanzanite, as a modern gem, does not have a long history of metaphysical lore in the sources. However, its addition to the birthstone list and its unique color-changing property have made it a symbol of individuality and modern elegance. The American Gem Trade Association's decision to add it suggests it was recognized for its unique beauty and desirability.
It is important to note that specific metaphysical claims (e.g., healing properties, astrological associations) are not detailed in the provided authoritative sources. The sources focus on historical use, geological origin, and gemological properties rather than unverified spiritual beliefs.
Care and Cleaning
The durability of each gemstone dictates the proper methods for care and cleaning, ensuring their longevity and beauty.
Turquoise, with its low hardness and porous nature, requires careful handling. It should be protected from chemicals, perfumes, and cosmetics, which can damage the stone or alter its color. Cleaning should be done with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals. It is best stored separately to prevent scratching.
Zircon, despite its relative hardness, is brittle and can be prone to chipping or breaking due to its perfect cleavage in one direction. It is sensitive to sudden temperature changes. Cleaning can be done with warm, soapy water and a soft brush. It is advisable to avoid ultrasonic cleaners and extreme heat. Given its brittleness, protective settings are recommended for jewelry intended for daily wear.
Tanzanite shares similar vulnerabilities with zircon. It has perfect cleavage, making it susceptible to breaking if struck. It is also sensitive to heat and rapid temperature changes. Cleaning should be gentle, using only warm, soapy water and a soft brush. Ultrasonic cleaners and steam cleaning are strongly discouraged. Due to its relative softness and cleavage, tanzanite jewelry should be worn with care and removed during activities that could subject it to impact.
Conclusion
The December birthstones—turquoise, zircon, and tanzanite—offer a remarkable diversity in color, history, and physical properties. From the ancient, opaque turquoise revered by Native American cultures to the brilliant, fire-filled zircon that once mimicked diamond, and the modern, pleochroic tanzanite from a single location in Tanzania, each gem provides a unique narrative. Their journey onto the official birthstone list reflects both tradition and evolution, with zircon joining in 1952 and tanzanite making a more recent entrance. While their gemological profiles differ—varying in hardness, cleavage, and treatment methods—all three require thoughtful care to preserve their beauty. For individuals born in December, this trio presents an unparalleled opportunity to select a birthstone that not only marks their birth month but also resonates with their personal style and appreciation for gems with deep geological and cultural roots.