The month of December is uniquely represented by three distinct birthstones: tanzanite, turquoise, and zircon. While all three are celebrated for their captivating blue hues, they differ profoundly in their geological origins, physical properties, and historical journeys. This article provides a detailed exploration of these three gems, drawing upon authoritative gemological data to guide enthusiasts, collectors, and prospective buyers. We will examine each stone’s history, formation, gemological characteristics, and symbolic significance, offering a comprehensive guide to the blue birthstones of winter.
History and Lore
The tradition of assigning specific stones to months has evolved over centuries, with December’s selection reflecting a blend of ancient heritage and modern discovery.
Turquoise boasts the longest history among the three. It has been used as a gemstone for thousands of years, with evidence of its use in the Southwestern United States dating back over 2,000 years. Here, Native American artists crafted beads, pendants, inlay work, and small sculptures from the stone. Turquoise remains an integral part of Southwestern culture today. Its status as a December birthstone is traditional; it appears on historical birthstone lists alongside lapis lazuli.
Zircon has a history of being mistaken for other, more valuable gems. Its high luster and colorful fire, similar to diamond, once led it to be used as a diamond alternative. As a modern birthstone, zircon was added to most lists in 1952, replacing lapis lazuli. This addition coincided with a period when topaz was relatively costly, though the discovery of large Brazilian topaz deposits later altered the market.
Tanzanite is the newest addition to the December family. It is a product of the 20th century, with its discovery and subsequent popularization occurring relatively recently. Its status as a birthstone was solidified through modern gemological marketing and trade associations, and it is now widely recognized as one of the three primary stones for December.
Geological Formation and Sources
Each of these gems forms under unique geological conditions and is sourced from specific regions of the world.
Turquoise is a hydrous phosphate of copper and aluminum. It forms in arid regions where acidic, copper-rich groundwater seeps through aluminum-bearing rocks. The mineral precipitates into veins, nodules, or crusts. The most prized turquoise often comes from Iran (historically known as Persian turquoise) and the Southwestern United States (notably Arizona, New Mexico, and Nevada). The color is directly influenced by the presence of copper (blue) and iron (green).
Zircon is a zirconium silicate (ZrSiO₄) that crystallizes from magma as it cools. It is one of the oldest minerals on Earth, found in many igneous and metamorphic rocks. Significant gem-quality zircon is mined in Sri Lanka, Cambodia, Myanmar, and Australia. Australian zircon, often found in sedimentary deposits, is particularly noted for its quality.
Tanzanite is the blue to violet variety of the mineral zoisite. Its formation is exceptionally rare, occurring only in a single, small mining area in the Merelani Hills of northern Tanzania. This geographic exclusivity is a key factor in its value and allure. The gem is formed through a complex process of metamorphism and hydrothermal alteration, where the presence of vanadium imparts its distinctive color.
Gemological Properties
Understanding the physical and optical characteristics of these gems is essential for identification, valuation, and care. The following table summarizes key properties, based on data from gemological sources.
| Property | Tanzanite | Turquoise | Zircon |
|---|---|---|---|
| Chemical Formula | Ca₂Al₃(SiO₄)₃(OH) | CuAl₆(PO₄)₄(OH)₈·4H₂O | ZrSiO₄ |
| Crystal System | Orthorhombic | Triclinic | Tetragonal |
| Hardness (Mohs) | 6.5 - 7 | 5 - 6 | 6.5 - 7.5 |
| Refractive Index | 1.69 - 1.70 | 1.61 - 1.65 | 1.92 - 2.01 |
| Specific Gravity | 3.35 | 2.6 - 2.9 | 4.6 - 4.7 |
| Typical Treatment | Heat | Stabilization, dyeing | Heat (often to enhance color) |
| Color Range | Blue to bluish violet to bluish purple | Blue to blue-green to yellowish green | Yellow, red, brown; heat-treated to blue, green, etc. |
Hardness and Durability: - Zircon is the hardest of the three (6.5-7.5 on the Mohs scale), making it relatively durable for jewelry, though it can be brittle due to its tetragonal crystal structure. - Tanzanite (6.5-7) is also fairly durable but requires careful handling to avoid chipping or abrasion. - Turquoise is the softest (5-6) and is porous. It is often stabilized (impregnated with a clear resin) to improve its durability and color consistency.
Color and Treatment: - Turquoise is prized for its sky-blue to greenish hues. Most turquoise on the market is treated to enhance color and stability. Natural, untreated turquoise of high quality is rare and valuable. - Zircon naturally occurs in yellow, red, and brown hues. The vibrant blue color that is most popular in the market (comprising about 80% of sold zircon) is achieved through heat treatment of brownish specimens. - Tanzanite is almost always heat-treated to transform its naturally brownish-yellow or greenish hues into the desirable blue-violet colors. This treatment is standard and accepted in the gem trade.
Symbolism and Metaphysical Beliefs
Across cultures and history, these stones have been imbued with symbolic meanings and metaphysical properties.
Turquoise has long been associated with protection, healing, and wisdom. In many Native American cultures, it is considered a sacred stone that connects the wearer to the sky and the earth. It is often seen as a symbol of good fortune and tranquility.
Zircon, due to its diamond-like brilliance, has historically been associated with wisdom, honor, and purity. It is sometimes believed to promote restful sleep and alleviate pain. Its varied colors have led to different associations; for example, golden zircon might be linked to prosperity.
Tanzanite, as a modern discovery, has quickly accumulated symbolic meaning. It is often called the "stone of transformation" and is believed to facilitate spiritual awakening, communication, and the manifestation of one's goals. Its unique blue-violet color is associated with calmness and intuition.
Care and Cleaning
Proper maintenance is crucial for preserving the beauty and longevity of these birthstones.
Turquoise: Due to its porosity and softness, turquoise is susceptible to damage from chemicals, heat, and prolonged exposure to water, which can cause fading or cracking. It should be cleaned with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals. Store it separately to prevent scratching.
Zircon: While harder, zircon can be brittle. It is best cleaned with warm water, mild soap, and a soft brush. Avoid sudden temperature changes and mechanical shocks. Ultrasonic cleaners are generally safe, but caution is advised for stones with inclusions or fractures.
Tanzanite: With a hardness of 6.5-7, tanzanite is moderately durable but can be prone to chipping if struck. It is sensitive to heat and should never be exposed to high temperatures (such as in a jeweler's torch or steam cleaner). Clean with warm, soapy water and a soft brush. Avoid ultrasonic cleaners and harsh chemicals.
Conclusion
The December birthstones—tanzanite, turquoise, and zircon—offer a remarkable spectrum of blue, from the sky-blue of turquoise to the violet-blue of tanzanite and the fiery blue of treated zircon. Each stone carries its own narrative: turquoise with its ancient cultural legacy, zircon with its historical mimicry of diamond and modern treatment, and tanzanite with its singular geographic origin and recent rise to prominence. For the gem enthusiast or jewelry buyer, understanding their distinct histories, properties, and care requirements allows for an informed appreciation of these three exceptional gems that brighten the darkest month of the year.