December, the last month of the Gregorian calendar, is rich not only in cultural traditions but also in the symbolic and geological significance of its birthstones. Unlike most months, which are associated with a single gemstone, December boasts a unique distinction—three birthstones: turquoise, tanzanite, and zircon, with blue zircon being a prominent variety. This multiplicity reflects both the historical evolution of birthstone lists and the desire to offer a range of affordable and meaningful options for jewelry. Each of these gemstones carries its own story of formation, symbolism, and historical use, making them fascinating subjects for gemological study and cultural appreciation.
This article will explore the rich history, geological properties, cultural symbolism, and practical care of these three December birthstones, drawing on the most authoritative and well-documented sources provided. We will also examine the reasons behind the inclusion of multiple stones for December, the timeline of their designation, and how they compare in terms of rarity, value, and aesthetic appeal.
Historical and Cultural Significance
The concept of birthstones is ancient and has evolved significantly over time. Initially, birthstones were derived from biblical references, such as the High Priest's breastplate described in the Book of Exodus, which listed twelve gemstones representing the twelve tribes of Israel. However, these early references did not specifically assign stones to months, and the modern birthstone system was not established until the 19th century.
The December birthstone list, in particular, has undergone notable changes. The earliest recorded December birthstone was ruby, based on the biblical gemstone list. However, by 1870, turquoise was designated as the primary December birthstone, a choice influenced by the popularity of the gem in Western fashion and jewelry, particularly through the influence of luxury brands like Tiffany & Co..
In 1912, the National Association of Jewellers (now the Jewellers of America) updated the list, retaining turquoise as the primary stone but also including lapis lazuli as an alternative. This dual designation reflected the growing interest in alternative gemstones and the desire to offer more options to consumers. In 1952, zircon—specifically blue zircon—was added to the list, marking a significant expansion of the December birthstone repertoire. Finally, in 2002, tanzanite was officially recognized as a December birthstone, a decision that was widely celebrated in the gemological community.
These changes highlight the dynamic nature of birthstone traditions and the influence of both cultural trends and the jewelry industry on their evolution. The inclusion of tanzanite, a gemstone discovered as recently as 1967, demonstrates how modern discoveries can reshape ancient practices.
Geological Formation and Sources
Each of December's birthstones has a unique geological origin and formation process, influenced by the chemical and environmental conditions in which they are formed.
Turquoise
Turquoise is a phosphate mineral composed of copper and aluminum. It forms in weathered copper ore deposits, typically in arid environments where water percolates through the rock and interacts with copper sulfides. This interaction creates an acidic solution that, when it comes into contact with aluminum and potassium in the surrounding rock, precipitates turquoise into cavities and cracks.
The formation of turquoise requires specific conditions: the presence of copper-rich rock, alkaline water, and a low-temperature environment. These conditions are commonly found in volcanic and sedimentary rock formations in arid regions. As a result, turquoise is typically found in countries with such geological profiles, including:
- Iran (historically the most famous source)
- China
- United States (particularly New Mexico and Arizona)
- Egypt (where it was historically mined and used by ancient pharaohs)
- Mexico
- Russia
Turquoise is a porous, opaque gemstone with a Mohs hardness of 5 to 6, making it relatively soft and prone to scratches and discoloration. It is often stabilized or treated with oils or resins to enhance its durability and color.
Tanzanite
Tanzanite is a trigonal mineral belonging to the columbite-tantalite group, and it is chemically a violet-blue variety of the mineral zoisite. It was first discovered in 1967 in Tanzania, specifically in the Merelani Hills near Arusha, which is the only place in the world where tanzanite is found. This exclusivity has contributed to its mystique and value.
Tanzanite forms under high-pressure, low-temperature conditions, typically in metamorphic rock formations. The intense pressure and specific chemical environment in the Merelani Hills create the conditions necessary for tanzanite to crystallize. The gemstone's violet-blue color is due to the presence of trivalent iron, and the color is often enhanced through heat treatment, which is a standard industry practice.
Tanzanite has a Mohs hardness of 6 to 7, making it relatively durable but still sensitive to impact and improper care. Its uniqueness and limited source have made it a highly sought-after gemstone, especially in the world of fine jewelry.
Zircon
Zircon is a zirconium silicate that occurs naturally in a wide range of colors, including red, orange, yellow, green, brown, and blue. The blue zircon often associated with December is created through heat treatment, which alters the gemstone's color from brown or yellow to a brilliant blue. This process is stable and does not affect the gemstone's durability.
Zircon forms in a variety of geological environments, including igneous, metamorphic, and sedimentary rocks, and it is often found in alluvial deposits. Major sources of zircon include:
- Australia
- Madagascar
- India
- Vietnam
- United States
Blue zircon has a Mohs hardness of 6 to 7.5, making it more durable than turquoise but less so than tanzanite. It is a double refractive gemstone, meaning it can display a play of light and a sparkling effect, which adds to its visual appeal.
Gemological Properties
Understanding the physical and optical properties of each December birthstone is essential for both gemologists and jewelry enthusiasts. These properties influence not only the gemstone's aesthetic appeal but also its durability, care requirements, and market value.
| Gemstone | Color Range | Hardness (Mohs) | Transparency | Refractive Index | Chemical Formula | Treatments Commonly Used |
|---|---|---|---|---|---|---|
| Turquoise | Blue to green | 5–6 | Opaque | 1.61–1.65 | CuAl₆(PO₄)₄(OH)₈·4H₂O | Oil, resin, dye |
| Tanzanite | Violet-blue | 6–7 | Transparent to translucent | 1.694–1.701 | Ca₂Al₃(SiO₄)(OH)₃·H₂O | Heat treatment |
| Zircon (Blue) | Blue (after heat treatment) | 6–7.5 | Transparent to translucent | 1.92–2.01 | ZrSiO₄ | Heat treatment |
Turquoise
- Color: Turquoise ranges from deep blue to greenish-blue, often with matrix patterns (veins of the host rock) that enhance its uniqueness.
- Hardness: 5 to 6 on the Mohs scale, making it relatively soft and prone to scratches.
- Transparency: Opaque, with some semi-translucent varieties.
- Refractive Index: 1.61 to 1.65.
- Chemical Formula: CuAl₆(PO₄)₄(OH)₈·4H₂O, a copper aluminum phosphate.
- Common Treatments: Turquoise is often oiled, waxed, or stabilized to enhance its color and durability.
Tanzanite
- Color: Violet-blue to purplish-blue, with a trichroic nature (it shows three different colors when viewed from different angles).
- Hardness: 6 to 7 on the Mohs scale, making it relatively durable.
- Transparency: Transparent to translucent.
- Refractive Index: 1.694 to 1.701.
- Chemical Formula: Ca₂Al₃(SiO₄)(OH)₃·H₂O, a hydrous calcium aluminum silicate.
- Common Treatments: Tanzanite is heat-treated to enhance its color. Untreated material is typically brown or yellow, and the violet-blue color is the result of controlled heating.
Zircon (Blue)
- Color: Blue, achieved through heat treatment of naturally occurring zircon.
- Hardness: 6 to 7.5 on the Mohs scale, making it more durable than turquoise but less so than tanzanite.
- Transparency: Transparent to translucent.
- Refractive Index: 1.92 to 2.01, which gives it a high refractive effect and sparkling appearance.
- Chemical Formula: ZrSiO₄, a zirconium silicate.
- Common Treatments: Blue zircon is heat-treated to achieve its characteristic blue color.
Symbolism and Metaphysical Beliefs
Each December birthstone has a rich symbolic and metaphysical history, with meanings that have evolved over time. These beliefs vary across cultures and eras, but they all contribute to the enduring appeal of these gemstones.
Turquoise
- Ancient Egypt: Turquoise was considered a sacred stone and was used in jewelry and amulets to protect the wearer. Pharaohs like King Tutankhamun were buried with turquoise jewelry, indicating its spiritual and protective significance.
- Ancient China: Chinese artisans carved turquoise into jade-like artifacts over 3,000 years ago. It was believed to bring good fortune and harmony.
- Modern Symbolism: Turquoise is associated with calm, protection, and spiritual clarity. It is often used in healing practices and is believed to enhance intuition and dispel negative energy.
Tanzanite
- Modern Symbolism: Tanzanite is relatively new to the birthstone list but has quickly gained popularity. It is associated with emotional healing, intuition, and spiritual awakening. Some believe it enhances empathy and compassion.
- Spiritual Properties: Tanzanite is said to open the third eye and heart chakras, promoting inner peace and emotional balance. It is also believed to help with decision-making and communication.
Zircon (Blue)
- Ancient Beliefs: Zircon has been used in jewelry for thousands of years, with ancient cultures attributing protective and healing properties to it. It was believed to ward off evil spirits and promote wisdom.
- Modern Symbolism: Blue zircon is associated with mental clarity, confidence, and enhanced creativity. It is believed to enhance focus and stimulate intellectual pursuits.
- Metaphysical Properties: Zircon is thought to boost energy levels and promote a sense of optimism. It is also used in spiritual practices to enhance communication with higher realms.
Care and Maintenance
Proper care and maintenance are essential to preserving the beauty and longevity of December birthstone jewelry. Each gemstone has specific needs due to its hardness, porosity, and sensitivity to chemicals and heat.
Turquoise
- Hardness: 5–6 on the Mohs scale.
- Porosity: Turquoise is porous and can absorb oils, lotions, and perfumes, which can cause it to lose color or become discolored.
- Cleaning: Clean turquoise with a soft cloth and mild soap and water. Avoid using ultrasonic or steam cleaners, as they can damage the stone.
- Storage: Store turquoise in a cool, dry place, preferably in a jewelry box or pouch to prevent scratches and exposure to chemicals.
Tanzanite
- Hardness: 6–7 on the Mohs scale.
- Porosity: Tanzanite is less porous than turquoise, but it is still sensitive to heat and chemicals.
- Cleaning: Use a soft cloth and mild soap and water. Avoid exposure to high heat, as it can alter the color of the stone.
- Storage: Store tanzanite in a jewelry box, preferably with soft lining, to prevent scratches and exposure to direct sunlight.
Zircon (Blue)
- Hardness: 6–7.5 on the Mohs scale.
- Porosity: Zircon is less porous than turquoise but still requires gentle care.
- Cleaning: Clean zircon with a soft cloth and mild soap and water. Avoid exposure to harsh chemicals or abrasive cleaners.
- Storage: Store zircon in a jewelry box, away from direct sunlight and heat, to preserve its color and clarity.
Conclusion
December's selection of birthstones—turquoise, tanzanite, and zircon—offers a rich tapestry of geological, historical, and symbolic significance. Each stone has its own unique properties, origins, and cultural meanings, making them not only beautiful adornments but also meaningful gifts that carry centuries of tradition and significance.
The evolution of the December birthstone list reflects the changing tastes and values of the jewelry industry and the enduring appeal of natural gemstones. From the ancient use of turquoise in Egyptian tombs to the modern discovery and popularization of tanzanite, these gemstones continue to captivate gemologists, jewelers, and collectors alike.
Whether you are drawn to the protective and calming properties of turquoise, the emotional and spiritual benefits of tanzanite, or the mental clarity and confidence-enhancing qualities of zircon, there is a December birthstone to suit every personality and preference.
By understanding the scientific and cultural background of these gemstones, you can make informed choices about how to care for and appreciate them, ensuring their beauty and value endure for generations.