December is a month of profound transitions, marked by the winter solstice in the Northern Hemisphere and the summer solstice in the Southern. It is a time of celebration, reflection, and natural phenomena, from the Geminid meteor shower to the long polar nights. For those born in this final month, their identity is intertwined with a unique group of birthstones: turquoise, zircon, and tanzanite. These three gems, while distinct in their geological origins and visual characteristics, are collectively celebrated as the traditional birthstones for December. Each stone carries its own rich history, lore, and scientific properties, offering a diverse palette of color and meaning for the December-born.
The tradition of assigning specific stones to months is a practice that has evolved over centuries, culminating in modern lists established by organizations like the American Gem Society. For December, the trio of turquoise, zircon, and tanzanite provides a range of options, from the ancient sky-blue of turquoise to the fiery brilliance of zircon and the velvety blue-violet of tanzanite. This article will delve into the history, lore, geological formation, and gemological properties of these three remarkable stones, exploring how each contributes to the rich tapestry of December's identity.
History and Lore
The history of December’s birthstones is a journey through time, from ancient civilizations to modern gemology. While the modern list is relatively recent, the individual stones have been prized for millennia.
Turquoise, perhaps the most ancient of the trio, has been a symbol of protection and good fortune for thousands of years. Its name derives from the French pierre turquoise, meaning "Turkish stone," reflecting its historical trade route from Persia to Europe. Ancient Egyptians adorned themselves with turquoise, believing it offered protection and connection to the divine. It was used in the elaborate burial masks of pharaohs and in elaborate jewelry. In the American Southwest, Native American cultures have held turquoise sacred for centuries, using it in ceremonies, jewelry, and art, where it is believed to be a piece of the sky that fell to earth. Its association with good fortune and success, as noted in historical accounts, has made it a perennial favorite.
Zircon boasts a history that is both long and sometimes confused. The term "zircon" likely comes from the Persian zargun, meaning "gold-colored," which reflects the stone’s common brownish-yellow hue. However, blue zircon has been particularly valued. In medieval Europe, zircon was believed to induce sound sleep, ward off evil, and bring prosperity. Its high refractive index and strong dispersion (fire) have made it a popular diamond simulant throughout history, often leading to confusion between the two. While it has been known since antiquity, its status as a December birthstone is a more modern development, solidified in the 20th century.
Tanzanite is the newest member of the December family. Its discovery is a recent event in gemological history, dating back to 1967. Found in the Merelani Hills of Tanzania, this blue-violet variety of the mineral zoisite was quickly recognized for its unique color and rarity. Its story is one of modern gemology, with its rapid rise to fame and its inclusion in the official birthstone list in 2002 by the American Gem Society. The stone’s name itself honors its country of origin, and its discovery is often cited as one of the most significant gemological finds of the 20th century. Some sources note that tanzanite is considered rarer than diamonds, a testament to its limited geographic source.
The journey of these stones to their official status as December birthstones was formalized through lists created by the American Gem Society and later adopted by the jewelry industry. While turquoise has long been associated with December, the inclusion of zircon and tanzanite reflects a broader, more inclusive understanding of the month’s gems, offering choices for different tastes and budgets.
Geological Formation and Sources
Understanding the origin of these stones requires a look at the diverse geological processes that create them and the specific locations where they are found.
Turquoise is a secondary mineral that forms in the arid regions of the world. It is not found in igneous or metamorphic rocks but rather forms in the near-surface environment where water containing dissolved copper and aluminum percolates through porous rock. This water evaporates, leaving behind the hydrated phosphate minerals that constitute turquoise. The most famous sources are in the American Southwest (Arizona, New Mexico, Nevada), where it is closely associated with copper deposits. Other significant sources include Iran (historically the finest "Persian turquoise"), China, and Egypt. The color and matrix (the host rock embedded in the stone) vary significantly by location, creating distinct regional varieties.
Zircon is a mineral that forms in a variety of rock types, particularly in igneous rocks like granite and metamorphic rocks. It is a common accessory mineral found in many geological environments. However, the gem-quality blue zircon used in jewelry is almost exclusively produced through heat treatment of brownish zircon crystals. These crystals are mined in several locations worldwide, with Cambodia and Sri Lanka being notable sources for material that turns a vivid blue upon heating. Other sources include Myanmar, Australia, and the United States. The natural blue color in zircon is extremely rare, and most commercial blue zircon on the market is the result of this thermal enhancement.
Tanzanite has the most restricted source of the three. It is found in only one location on Earth: the Merelani Hills in the Lelatema Mountains of northern Tanzania, near Mount Kilimanjaro. This unique geological environment, where specific conditions of heat and pressure transformed zoisite into tanzanite, has led to its extreme rarity. Mining occurs in four small blocks within this area, and the supply is finite. The stone’s formation is linked to a tectonic event that occurred over 500 million years ago, making it a geological marvel. Its scarcity is a key factor in its value and appeal.
Gemological Properties
The three December birthstones differ significantly in their physical and optical properties, which affect their durability, appearance, and care requirements.
| Property | Turquoise | Zircon (Blue) | Tanzanite |
|---|---|---|---|
| Chemical Formula | Hydrated copper aluminum phosphate | ZrSiO₄ (Zirconium silicate) | Ca₂(Al,OH)₂(SiO₄) (Zoisite variety) |
| Crystal System | Triclinic | Tetragonal | Orthorhombic |
| Hardness (Mohs) | 5 - 6 | 6.5 - 7.5 | 6.5 - 7 |
| Refractive Index | 1.610 - 1.650 | 1.925 - 2.013 | 1.691 - 1.700 |
| Specific Gravity | 2.60 - 2.90 | 4.60 - 4.70 | 3.35 |
| Color | Sky blue, blue-green, green | Colorless, yellow, brown, red, blue (heated) | Blue, violet, brownish (heated) |
| Durability | Low; porous, susceptible to cracking and discoloration | Good; can be brittle due to cleavage | Fair to good; can be brittle due to cleavage |
Turquoise is the softest and most fragile of the three. With a hardness of 5 to 6 on the Mohs scale, it is easily scratched and can be damaged by chemicals, sweat, and cosmetics. Its porous nature means it can absorb liquids and oils, which may alter its color over time. High-quality turquoise is often stabilized with resins to enhance its durability and color consistency. The presence of a matrix (the host rock) is common and is often valued for the unique patterns it creates.
Zircon is the hardest of the trio, with a hardness of 6.5 to 7.5, making it suitable for jewelry, though its brittleness requires careful setting. Its most remarkable optical property is its high refractive index, which gives it exceptional brilliance and fire, often exceeding that of a diamond. This "fire" is the dispersion of light into spectral colors, a characteristic that makes blue zircon particularly dazzling. However, zircon can have strong cleavage in some directions, making it vulnerable to impact if struck at the wrong angle. The blue color in commercial zircon is almost always the result of heat treatment, a stable and permanent process.
Tanzanite has a hardness of 6.5 to 7, similar to zircon, but it is also noted for its strong trichroism—the ability to show three different colors (blue, violet, and burgundy) when viewed from different crystal directions. This property makes the cutting of tanzanite a skilled art, as cutters must orient the stone to display its most desirable blue-violet hue. Like zircon, tanzanite can have cleavage planes, making it susceptible to breakage if struck. Most tanzanite on the market is heat-treated to remove brownish components and achieve the vivid blue color for which it is famous. This treatment is considered permanent and is widely accepted in the gem trade.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, these stones are steeped in symbolism and metaphysical lore, beliefs that have persisted for centuries.
Turquoise is universally regarded as a stone of protection, healing, and good fortune. In many cultures, it is believed to ward off negative energy and bring calm and balance to the wearer. It is often associated with the throat chakra, believed to aid in communication and self-expression. Its connection to the sky and water in Native American lore reinforces its symbolism of life, wisdom, and spiritual grounding. The stone’s ability to change color was historically seen as a warning of danger or illness, adding to its mystical reputation.
Zircon has a long history of metaphysical associations. It is often linked to prosperity, honor, and wisdom. In some traditions, it is believed to promote sound sleep and protect travelers. The blue variety, in particular, is associated with clarity of thought and spiritual growth. Its diamond-like appearance has led to it being called the "Meditation Stone," thought to help in connecting with higher realms of consciousness. While these beliefs are not scientifically verified, they contribute to the stone’s enduring appeal.
Tanzanite, as a modern discovery, has quickly developed its own set of symbolic meanings. It is often associated with transformation, intuition, and spiritual awareness. Its unique blue-violet color is said to stimulate the throat and third-eye chakras, enhancing communication and psychic abilities. Some believe it brings a sense of calm and a connection to higher guidance. Given its rarity, it is also seen as a stone of abundance and a symbol of a unique destiny.
It is important to note that these metaphysical beliefs are part of cultural and personal traditions and are not recognized by scientific gemology. They add a layer of meaning and personal connection for many wearers.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of these birthstones, with requirements varying significantly based on their properties.
Turquoise requires the most careful handling. Due to its porosity and softness, it should be cleaned only with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals, including household cleaners and cosmetics. It is best to put turquoise jewelry on after applying lotions and perfumes. Store it separately to avoid scratches from harder materials. For stabilized turquoise, mild soap and lukewarm water can be used with a soft brush, but it must be dried immediately and thoroughly.
Zircon is more durable but still requires caution. Its brittleness means it can be chipped or cracked by a hard blow. It is generally safe to clean with warm soapy water and a soft brush. Avoid ultrasonic cleaners, as vibrations can cause fractures in stones with inclusions or cleavage. Sudden temperature changes should also be avoided, as they can cause thermal shock. Store zircon separately to prevent scratching other gems or being scratched itself.
Tanzanite, with its hardness of 6.5 to 7, is moderately durable but is prone to chipping and cracking due to its cleavage. It is sensitive to rapid temperature changes and should not be exposed to extreme heat. Cleaning should be done gently with warm soapy water and a soft brush. Ultrasonic cleaners and steam cleaning are not recommended, as they can damage the stone. It is also advised to remove tanzanite jewelry during strenuous activities to avoid impact. Professional cleaning and inspection by a jeweler are recommended for pieces set in rings or bracelets.
Conclusion
The birthstones of December—turquoise, zircon, and tanzanite—offer a captivating spectrum of color, history, and meaning. From the ancient, protective sky-blue of turquoise to the brilliant, fire-filled blue of heat-treated zircon and the rare, trichroic blue-violet of tanzanite, each stone provides a unique connection to the month’s spirit. Their stories are woven from the fabric of geology, history, and human belief, spanning from the arid mines of the American Southwest to the volcanic hills of Tanzania. For those born in December, these gems are more than mere adornments; they are tangible links to a rich heritage of natural beauty and cultural significance, offering a personal stone that resonates with their individual identity and style.