The month of December is uniquely associated with three distinct birthstones: tanzanite, turquoise, and zircon. This trio offers a remarkable spectrum of blue hues, from the deep violet-blue of tanzanite to the sky-blue of turquoise and the brilliant fire of zircon. Each stone possesses its own unique geological origin, historical significance, and gemological characteristics. While modern lists often present these options, traditional lists also include turquoise and lapis lazuli for December, reflecting the evolving nature of birthstone selections over time. This article provides a detailed exploration of these three December birthstones, drawing upon their geological formation, gemological properties, historical lore, and practical care, offering gemstone enthusiasts and collectors a thorough understanding of these captivating gems.
Historical and Cultural Significance
The concept of birthstones has ancient roots, with the modern list standardized in 1912. However, the tradition of associating specific gems with months or zodiac signs dates back centuries. For December, the stones have seen additions and changes, with tanzanite being a very recent addition in the 20th century, while turquoise and zircon have longer, more storied histories.
Turquoise holds one of the longest histories as a gemstone, with evidence of its use spanning over 2000 years. In the Southwestern United States, Native American cultures utilized turquoise extensively for beads, pendants, inlay work, and small sculptures, embedding it deeply into their artistic and cultural traditions. This ancient usage established turquoise as a stone of historical and cultural importance long before its formal adoption as a birthstone. Its enduring appeal is evident in its continued significance in Southwestern culture today.
Zircon is another gem with a venerable history, though the provided sources focus primarily on its visual properties rather than its ancient lore. It is noted for its bright appearance and high luster, with some specimens producing a colorful fire similar to that of diamond. This characteristic has likely contributed to its desirability across various periods.
Tanzanite is the newest member of the December birthstone family. Its history is intrinsically linked to its discovery, which occurred relatively recently. The sources indicate that tanzanite was added to the modern birthstone list in 1952. Prior to this, topaz was listed as a December birthstone, but the discovery of large topaz deposits in Brazil reduced its cost, and tanzanite was introduced as a new, valuable alternative. This addition reflects the dynamic nature of the modern birthstone chart, which continues to evolve to include newly discovered and popular gemstones.
The modern birthstone lists for December, as compiled from multiple sources, consistently include tanzanite, turquoise, and zircon. Some lists also note blue zircon and blue topaz as alternatives, though the primary trio remains the focus. The traditional list for December, which often includes turquoise and lapis lazuli, shows the historical preferences that predate the modern standardization.
Geological Formation and Sources
Understanding the geological origins of these birthstones provides insight into their rarity, value, and unique characteristics. Each of the three December stones forms under different conditions and is sourced from distinct regions of the world.
Tanzanite is a variety of the mineral zoisite. Its formation is geologically unique, occurring in a very limited area. The primary and most significant source of tanzanite is the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. This singular source location contributes to its rarity and value. The geological conditions required for its formation are specific, making it one of the rarest gemstones in the world.
Turquoise is a hydrous phosphate of copper and aluminum. It forms in arid regions where acidic, copper-rich groundwater seeps through and reacts with minerals containing aluminum and phosphorus, such as feldspar. The sources mention that turquoise has been mined in the Southwestern United States for thousands of years, with this region being a historically and culturally significant source. Other notable sources include Iran, which is famous for its high-quality "Persian turquoise," and China, Egypt, and Mexico. The color of turquoise is heavily influenced by its copper content (which provides the blue hue) and the presence of iron (which can create greenish tones).
Zircon is a zirconium silicate mineral 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 is found worldwide, the sources specifically highlight its occurrence in various regions, though they do not list specific countries for the December birthstone zircon. However, gem-quality zircon is notably mined in countries such as Cambodia, Myanmar, Sri Lanka, Australia, and the United States. The gem's formation often involves high temperatures and pressures, and it can be found in a range of colors, with the blue variety being particularly popular for December.
The sources also note that large deposits of topaz were discovered in Brazil, which reduced its price and contributed to its replacement in some lists by tanzanite. This highlights how new mining discoveries can influence the market and birthstone charts.
Gemological Properties
A detailed examination of the gemological properties of tanzanite, turquoise, and zircon reveals their distinct characteristics, which affect their durability, appearance, and care requirements.
Tanzanite is a relatively recent addition to the gemological world, and its properties are well-documented. It is a variety of zoisite, with a chemical formula of Ca2Al3(SiO4)3(OH). On the Mohs scale of hardness, tanzanite ranks between 6 and 7, making it moderately durable but susceptible to scratching and breakage if not handled with care. The sources specifically note that tanzanite has "perfect cleavage and will break easily," which is a critical consideration for jewelers and wearers. Its most prized color is a vivid violet-blue, often described as "sapphire blue," and it is typically heat-treated to enhance its color. The refractive index of tanzanite ranges from approximately 1.69 to 1.70, and it exhibits strong pleochroism, showing different colors (blue, violet, and burgundy) when viewed from different angles.
Turquoise is an opaque mineral with a chemical formula of CuAl6(PO4)4(OH)8·4H2O. It has a relatively low hardness, typically between 5 and 6 on the Mohs scale, which makes it prone to scratching. The sources explicitly state that turquoise has a "low hardness and is easily scratched." Its opacity means it is almost always cut as a cabochon (a smooth, rounded dome) rather than faceted. The color ranges from sky blue to blue-green to yellowish green, with the most prized being a bright, even blue. The presence of the host rock (matrix) can create attractive patterns, such as the "spiderweb" matrix found in some specimens. Turquoise is also porous and can be susceptible to chemicals, oils, and changes in humidity, which can affect its color and stability over time.
Zircon is a gemstone with exceptional optical properties. Its chemical formula is ZrSiO4. It ranks high on the Mohs scale, with a hardness of 7 to 7.5, making it significantly more durable than tanzanite and turquoise. However, zircon is also known for its brittleness and can be prone to chipping due to its perfect cleavage in one direction. The sources highlight zircon's "high luster" and its ability to produce "colorful fire that is similar to diamond," referring to its high refractive index (1.92 to 2.01) and strong dispersion (0.039), which gives it brilliant sparkle. Zircon occurs in a variety of colors, but the blue variety, often achieved through heat treatment of brown zircon, is the most common for December. It is typically faceted to maximize its brilliance.
The following table summarizes key gemological properties of the three December birthstones, based on the information provided in the sources:
| Property | Tanzanite | Turquoise | Zircon |
|---|---|---|---|
| Chemical Formula | Ca2Al3(SiO4)3(OH) | CuAl6(PO4)4(OH)8·4H2O | ZrSiO4 |
| Mohs Hardness | 6 - 7 | 5 - 6 | 7 - 7.5 |
| Crystal System | Orthorhombic | Triclinic | Tetragonal |
| Key Optical Property | Strong Pleochroism | Opaque (no refraction) | High Refractive Index, Dispersion |
| Typical Cut | Faceted | Cabochon | Faceted |
| Common Treatments | Heat treatment for color | Stabilization, dyeing | Heat treatment for color |
| Durability Notes | Moderate; perfect cleavage | Low hardness; easily scratched | Brittle; perfect cleavage |
Symbolism and Metaphysical Beliefs
While gemological properties are grounded in science, the symbolic and metaphysical beliefs associated with gemstones are part of their cultural legacy. The provided sources offer limited information on this aspect, focusing more on historical use and physical characteristics. However, some general beliefs can be inferred from common knowledge, though it is important to note that these are not explicitly supported by the provided chunks.
Turquoise has long been associated with protection, healing, and good fortune. In many cultures, including those of the Native American Southwest, Iran, and ancient Egypt, it was believed to ward off evil and bring health. Its blue color is often linked to the sky and water, symbolizing tranquility and peace.
Zircon, with its diamond-like fire, has historically been associated with wisdom, honor, and purity. In some traditions, it was believed to promote sleep and ward off evil spirits. The blue variety, in particular, is sometimes linked to calmness and clarity of thought.
Tanzanite, as a modern discovery, lacks the ancient lore of turquoise and zircon. However, it has quickly been adopted into metaphysical circles, where it is often associated with spiritual awakening, transformation, and enhanced intuition. Its unique violet-blue color is said to stimulate the higher chakras and promote a connection to higher consciousness.
It is crucial to approach these metaphysical claims with an understanding that they are based on tradition and belief rather than scientific evidence. The sources provided do not delve into these aspects, so such information should be considered supplementary to the gemological and historical facts.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone. The differing physical properties of tanzanite, turquoise, and zircon necessitate specific care instructions.
Tanzanite requires careful handling due to its perfect cleavage and moderate hardness. It should be protected from sharp blows and extreme temperature changes, which can cause cracking. Cleaning should be done with warm, soapy water and a soft brush. Ultrasonic cleaners and steam cleaners are not recommended, as the vibrations and heat can damage the stone. Given its cleavage, it is best to store tanzanite jewelry separately to avoid contact with harder gems that could scratch it.
Turquoise, with its low hardness and porous nature, is the most delicate of the three. It is susceptible to scratches, chemicals, and changes in humidity. Many turquoise stones are treated (stabilized) to improve durability, but care is still necessary. Clean turquoise with a soft, dry cloth; avoid water and chemicals, which can seep into the stone and alter its color or cause damage. Do not use ultrasonic cleaners or steam. Store turquoise away from direct sunlight and extreme temperatures to prevent fading or cracking.
Zircon, despite its higher hardness, is brittle and has perfect cleavage. It can chip or break if subjected to a sharp impact. It is generally safe to clean with warm, soapy water and a soft brush. However, like tanzanite, it should be kept away from ultrasonic cleaners and steam due to the risk of exacerbating any existing fractures. When storing zircon jewelry, ensure it is padded and kept separate from other stones to prevent chipping.
Conclusion
The three birthstones of December—tanzanite, turquoise, and zircon—offer a captivating study in diversity. From the ancient, culturally rich turquoise to the billion-year-old zircon and the modern marvel of tanzanite, each gem tells a unique story of geological formation, historical significance, and gemological wonder. Their shared association with the color blue provides a thematic link, yet their individual characteristics—from hardness and cleavage to origin and treatment—demand distinct appreciation and care. For those born in December, this trio provides a range of choices, allowing for personal expression based on color preference, durability needs, and historical resonance. As with all gemstones, understanding their properties and respecting their vulnerabilities ensures that these birthstones can be cherished for generations.