The month of December is uniquely represented in the world of gemstones by a trio of distinct and captivating gems: turquoise, tanzanite, and zircon. Unlike months with a single birthstone, December offers a spectrum of blue, from the earthy, opaque turquoise to the vivid, pleochroic tanzanite and the brilliant, multifaceted zircon. Each stone carries its own history, geological origin, and set of properties, providing those born in the final month of the year with a diverse array of choices. This article delves into the characteristics, lore, and practical aspects of these three December birthstones, drawing upon gemological data and historical context to provide a comprehensive guide for enthusiasts, collectors, and jewelry buyers.
History and Lore
The historical significance of each December birthstone is as varied as their colors. Turquoise holds the distinction of being one of the oldest known gemstones, with a legacy deeply rooted in the ancient cultures of the Americas. In the Southwestern United States, Native Americans were utilizing turquoise over 2,000 years ago, crafting it into beads, pendants, intricate inlay work, and small sculptures. This ancient artistry cemented turquoise's role not merely as an ornament but as a culturally significant material, a tradition that continues to be an important part of Southwestern culture today. Its enduring appeal is partly due to its accessibility; turquoise jewelry is generally not extremely expensive, making genuine turquoise an affordable option for many.
Zircon's history is intertwined with its remarkable visual properties. For centuries, it has been prized for its high luster and colorful fire, which closely resembles that of diamond. This similarity led to zircon being used historically as a diamond alternative, a role it fulfilled before the advent of modern simulants like cubic zirconia. Its journey to becoming a modern birthstone is a more recent development. According to the provided materials, zircon replaced lapis lazuli as a birthstone for December in 1952. This change was part of a broader update to birthstone lists, which also included the addition of other stones like spinel and citrine as modern alternatives.
Tanzanite is the newest member of the December birthstone family. While its history is not as ancient as turquoise's, its rapid rise to prominence is notable. The provided sources indicate that it was added to most birthstone lists in 1952, the same year as zircon's inclusion. At that time, topaz was a relatively costly gem, but the discovery of large deposits in Brazil subsequently reduced its price, making it more accessible. Tanzanite's addition reflects the evolving nature of birthstone lists, which continue to incorporate new and popular gemstones. Its unique color-changing property—a feature where the stone appears to shift from blue to bluish purple to bluish violet depending on the viewing angle—has contributed significantly to its modern appeal.
Geological Formation and Sources
The origins of these three gems are as diverse as their appearances. Turquoise is an opaque mineral, a hydrous phosphate of copper and aluminum. Its formation is closely tied to specific geological environments where acidic, copper-rich waters interact with aluminum-bearing rocks. This process can occur in arid regions, which explains its prevalence in the Southwestern United States and other desert areas globally. The material is often found in veins or nodules within host rock, which is why it is typically cut into cabochons, often freeform shapes, to maximize the use of the rough material rather than being cut into standardized calibrated shapes.
Zircon is a mineral with the chemical formula ZrSiO₄. It forms in a variety of rock types, including igneous and metamorphic rocks. As a durable and resistant mineral, it can survive weathering processes and be found in sedimentary deposits. While the provided sources do not specify current mining locations for zircon, its widespread occurrence in nature is well-established in gemological literature. The sources do note that most natural zircons are found in yellow, red, or brown colors, with the more popular blue color being predominantly the result of heat and irradiation treatments applied to these naturally occurring stones.
Tanzanite, a variety of the mineral zoisite, has a much more localized geological origin. It is found only in a single, small mining area in the Merelani Hills of Tanzania, near the base of Mount Kilimanjaro. This extreme rarity of source is a key factor in its value and allure. The formation of tanzanite is associated with the unique geological conditions of this region, where heat and pressure have transformed the original zoisite into the blue-violet variety. The vast majority of tanzanite sold in jewelry today has been heat-treated to achieve its signature blue to bluish violet color, a stable treatment that enhances the stone's natural hue.
Gemological Properties
Understanding the physical and optical properties of each gemstone is crucial for proper identification, care, and appreciation. The following table summarizes key gemological data for the three December birthstones, based on the information provided in the sources.
| Gemstone | Chemical Composition | Hardness (Mohs Scale) | Typical Colors | Key Optical/Physical Features | Common Treatments |
|---|---|---|---|---|---|
| Turquoise | Hydrous copper aluminum phosphate | Not specified in sources | Blue to blue-green to yellowish green | Opaque; often found in nodules or veins. | Generally not treated, though stabilization is common in the trade. |
| Tanzanite | Calcium aluminum hydroxyl sorosilicate (Zoisite) | Not specified in sources | Blue, bluish purple, bluish violet | Pleochroic (color shifts with viewing angle); often transparent. | Heat treatment is standard to develop the blue color. |
| Zircon | Zirconium silicate (ZrSiO₄) | Not specified in sources | Natural: yellow, red, brown. Treated: blue, green, others. | High luster; high refractive index gives it a "fire" similar to diamond. | Heat and irradiation treatments are common to produce blue, green, and other colors. |
Turquoise: As an opaque mineral, turquoise's value is primarily judged by its color and matrix (the host rock inclusions). The most prized color is a bright, even sky blue, free from dark veining or mottling. Its hardness is not specified in the provided chunks, but it is generally known in the gemological community to be relatively soft (typically 5 to 6 on the Mohs scale), which makes it durable enough for jewelry but susceptible to scratches and chemical damage. Its opacity means it is always cut en cabochon.
Tanzanite: This gemstone is prized for its transparency and vivid color. Its most defining characteristic is its strong pleochroism, meaning it displays different colors when viewed from different crystallographic directions. The primary color seen in cut stones is a rich blue-violet, but it can show reddish or greenish tints depending on the orientation. While its hardness is not listed in the sources, it is moderately hard (around 6.5 to 7 on the Mohs scale), making it suitable for jewelry but requiring some care to avoid impact damage.
Zircon: Zircon is renowned for its exceptional brilliance and fire, which rival those of diamond. Its high refractive index and strong dispersion contribute to this effect. The natural color range of zircon is broad, but the market is dominated by blue zircon, which is almost always the result of treating brown or yellowish zircons with heat. This treatment is stable and widely accepted in the trade. The hardness of zircon is significant; it is a relatively hard and durable gemstone (around 7.5 on the Mohs scale), though it can be brittle and susceptible to cleavage, requiring careful handling during cutting and setting.
Symbolism and Metaphysical Beliefs
The symbolic meanings attributed to these stones are drawn from both ancient traditions and modern interpretations, as reflected in the provided materials.
Turquoise is deeply associated with protection and healing. Its long history in Native American culture imbues it with a sense of connection to the earth and ancestral wisdom. In many cultures, it is considered a protective talisman against negative forces and is believed to bring good fortune and health. Its calming blue-green hues are often linked to tranquility and emotional balance.
Tanzanite, as a newer gemstone, has developed its own set of modern metaphysical associations. It is often linked to transformation, vision, and spiritual awakening. Its unique color-changing property is sometimes interpreted as a symbol of higher consciousness and the ability to see beyond the ordinary. Some modern sources suggest it promotes calm and clarity, though this is not widely accepted in formal gemology.
Zircon carries the legacy of its historical use as a diamond substitute, which associates it with clarity, purity, and prosperity. It is believed to enhance self-confidence and promote spiritual growth. The blue variety, in particular, is linked to peace and tranquility. While these beliefs are popular in crystal healing circles, they are not supported by scientific evidence and should be considered as part of the stone's cultural lore rather than its proven properties.
Care and Cleaning
Proper maintenance is essential to preserve the beauty and longevity of any gemstone jewelry. The care instructions for each December birthstone are dictated by their inherent physical properties.
Turquoise, due to its relative softness and porosity, requires gentle care. It should be cleaned with a soft, damp cloth and mild soap. Avoid harsh chemicals, ultrasonic cleaners, and steam cleaners, as these can damage the stone or its surface treatment (many turquoise stones are stabilized with wax or resin). It is also advisable to remove turquoise jewelry before engaging in physical activities or applying cosmetics, lotions, or hairsprays, which can cause discoloration over time.
Tanzanite is moderately hard but can be brittle. It is best cleaned with warm water, a mild detergent, and a soft brush. Ultrasonic cleaners and steam cleaning are not recommended, as the vibrations and heat can cause fractures in the stone. Due to its pleochroism, the cut of the stone is critical to displaying its best color, so it should be handled with care to avoid chips or scratches that could affect its appearance.
Zircon is relatively hard but can be brittle, making it susceptible to chipping if struck against a hard surface. It is generally safe to clean with warm soapy water and a soft brush. However, some heat-treated zircons, particularly blue zircon, may be sensitive to extreme temperature changes. As with all gemstones, it is prudent to avoid exposing zircon to harsh chemicals, ultrasonic cleaners, and steam. Storing zircon jewelry separately from other pieces can prevent scratching due to its hardness.
Conclusion
The birthstones of December—turquoise, tanzanite, and zircon—offer a remarkable diversity in color, origin, and history. Turquoise connects us to ancient traditions and the earth, with its opaque, soothing hues. Tanzanite represents modernity and rarity, captivating with its dynamic color change and singular source. Zircon combines historical significance with brilliant optical properties, providing a durable and fiery alternative to diamond. Together, they provide a rich palette from which December-born individuals can choose a gemstone that resonates with their personal style and appreciation for natural beauty. Understanding their geological backgrounds, gemological properties, and care requirements allows for a deeper appreciation of these remarkable minerals and ensures their preservation for generations to come.