December is uniquely represented in the modern birthstone chart by a trio of captivating blue gems: tanzanite, turquoise, and zircon. Each stone offers a distinct shade of blue, from the violet-tinged hues of tanzanite to the sky-like serenity of turquoise and the brilliant fire of zircon. This variety provides those born in the final month of the year with a spectrum of choices, allowing for personal expression in jewelry. While all three are celebrated as December birthstones, their histories, geological origins, and gemological properties are remarkably diverse. This article explores the unique characteristics of each stone, from their formation deep within the Earth to their journey into the human world as symbols of protection, healing, and wisdom.
History and Lore
The history of these December birthstones spans millennia and continents, with each stone carrying its own narrative of cultural significance and tradition.
Turquoise holds the most ancient legacy among the trio. Its use as a gemstone dates back over two thousand years in the Southwestern United States, where Native American artists crafted intricate beads, pendants, inlay work, and small sculptures from the material. Turquoise remains an integral part of Southwestern culture today, deeply embedded in its artistic and spiritual traditions. For centuries, this opaque, sky-blue mineral has been associated with protection and health across various cultures.
Zircon, another December birthstone, is one of the oldest minerals on Earth, with some specimens dating back billions of years. However, its history as a popular gemstone is more recent. Known for its exceptional brightness and high luster, zircon can produce a colorful fire that rivals even diamond. Historically, it has been used to mimic more expensive gems, but its own unique qualities have earned it a place of distinction. Its association with December is a modern development, though its presence in jewelry spans centuries.
Tanzanite is the newest addition to the December birthstone family. Discovered in the late 20th century, it was formally added to the modern birthstone list by the American Gem Trade Association in 2002, marking the first change to the official list in 50 years. Its rapid rise to prominence is a testament to its unique beauty. While it lacks the ancient history of turquoise or zircon, its lore is tied to its singular source and the modern gemological world's fascination with its vivid color.
The modern birthstone chart itself is a product of standardization efforts. The National Association of Jewelers (now Jewelers of America) established the first official birthstone chart in the United States, creating a list that is still widely used. Over time, this list has been updated to include new discoveries and alternatives, reflecting both geological discoveries and market trends. For December, this evolution has resulted in a trio of stones, offering a range of colors and price points. Traditional charts also include lapis lazuli as an alternative for December, though modern lists primarily feature the blue trinity.
Geological Formation and Sources
The formation of these gems occurs under vastly different geological conditions, leading to their unique appearances and physical properties.
Turquoise is a secondary mineral formed by the interaction of water with pre-existing rocks containing copper and aluminum. It is found in arid regions where water percolates through copper-rich rocks, depositing the mineral in veins or nodules. The most significant sources of turquoise are in the Southwestern United States, particularly in Arizona, New Mexico, and Nevada, where it has been mined for centuries. Other notable sources include Iran, China, and Egypt. The color of turquoise varies based on its copper (blue) and iron (green) content, with the most prized pieces exhibiting a bright, even blue hue.
Zircon is a primary mineral, meaning it crystallizes directly from magma as it cools. It is commonly found in igneous and metamorphic rocks worldwide. Significant zircon deposits are located in Australia, Cambodia, Myanmar, and Sri Lanka. Australian zircon, for example, often exhibits a rich golden-brown color, while stones from Southeast Asia can display a range of hues. The gem's formation in high-temperature environments contributes to its hardness and durability, though it can be prone to breakage due to its cleavage.
Tanzanite has a remarkably specific origin. It is found in only one place on Earth: a small, four-square-kilometer mining area in the Merelani Hills of northern Tanzania. The stone is a variety of the mineral zoisite and forms during the metamorphism of certain rocks. Its formation is linked to the tectonic activity in the East African Rift Valley. Due to its extremely limited geographic source, tanzanite is considered rarer than diamond. Mining is conducted on a small scale, and the supply is carefully controlled to maintain its value and exclusivity.
While all three stones are mined around the world, their sources are distinct. Turquoise is sourced primarily from the American Southwest and parts of Asia and the Middle East. Zircon comes from a broader range of global locations, with Australia being a leading producer. Tanzanite's source is singular and exclusive to Tanzania, making it a unique gem in the mineral kingdom.
Gemological Properties
Understanding the physical and optical properties of these gems is essential for appreciation, identification, and care. The following table summarizes key gemological data for the three December birthstones, based on information from the provided sources.
| Gemstone | Chemical Composition | Hardness (Mohs Scale) | Key Characteristics | Typical Cut |
|---|---|---|---|---|
| Turquoise | Hydrated copper aluminum phosphate | 5 - 6 | Opaque, color ranges from blue to blue-green to yellowish green. Low hardness makes it easily scratched. | Cabochon (often freeform) |
| Zircon | Zirconium silicate (ZrSiO₄) | 6.5 - 7.5 | High luster, bright gem, can produce colorful fire similar to diamond. Prone to breakage. | Faceted (brilliant or step cuts) |
| Tanzanite | Calcium aluminum hydroxyl sorosilicate | 6.5 - 7 | Trichroic (shows blue, violet, and burgundy), perfect cleavage. | Faceted (brilliant or step cuts) |
Turquoise is an opaque mineral, meaning light does not pass through it. This opacity dictates its typical use in jewelry. It is most often cut into cabochons—smooth, rounded, polished domes—rather than faceted shapes. Freeform cuts are common to maximize the use of the rough material. Its hardness on the Mohs scale ranges from 5 to 6, which is relatively low. This makes turquoise susceptible to scratching and damage from chemicals, acids, and even perspiration. Bright blue is the most preferred color, and the finest specimens exhibit an even, vibrant hue without matrix (the host rock) veining.
Zircon is a transparent gemstone with a high refractive index, giving it exceptional brilliance and fire. Its luster is bright, and its fire can mimic the sparkle of a diamond. While it has a good hardness of 6.5 to 7.5, zircon is brittle and possesses perfect cleavage in two directions. Cleavage is a tendency to break along flat planes of weakness in the crystal structure. This makes zircon vulnerable to breakage during cutting, setting, and wear. It is typically faceted to enhance its brilliance and is available in a variety of cuts, including brilliant and step cuts. Colorless zircon is often used as a diamond simulant, but blue zircon is a popular December birthstone.
Tanzanite is a transparent to translucent variety of zoisite. Its most famous property is its strong trichroism—the ability to display three different colors when viewed from different crystallographic directions. Typically, it shows blue, violet, and burgundy tones. The most valued color is an intense, saturated blue to violet. Like zircon, tanzanite has perfect cleavage, making it brittle and prone to chipping or breaking if struck. It has a hardness of 6.5 to 7, which is moderate but requires careful handling. Most tanzanite is heat-treated to enhance its blue color, a standard and accepted practice in the gem trade. It is usually faceted in brilliant or step cuts to maximize its color and clarity.
Symbolism and Metaphysical Beliefs
Across cultures and history, gemstones have been imbued with symbolic meanings and metaphysical powers. The December birthstones are no exception, each carrying a legacy of belief.
Turquoise is perhaps the most symbolically rich of the three. In Southwestern Native American cultures, it is considered a sacred stone, representing the sky and water. It is believed to offer protection, healing, and good fortune. Historically, it was used as a talisman against injury and evil. Its connection to the sky and water links it to tranquility, peace, and emotional balance. The stone is also associated with wisdom, truth, and the alleviation of negative energy.
Zircon has been associated with wisdom, honor, and purity. In some traditions, it is believed to promote prosperity and attract success. Its brilliant fire has linked it to light and clarity of thought. Some historical beliefs suggest that zircon can help with sleep when placed under a pillow and can ward off nightmares. While its metaphysical properties are less documented than turquoise's, it is often seen as a stone of spiritual grounding and protection.
Tanzanite, as a modern discovery, has quickly developed its own lore. It is often called the "stone of transformation" and is believed to facilitate a higher consciousness, intuition, and spiritual perception. Its unique color and rarity are associated with individuality and vision. Some believe it can open the mind to new possibilities and help in understanding one's purpose. Its calming blue and violet hues are also linked to tranquility and stress relief.
While these metaphysical beliefs are part of the cultural fabric surrounding these gems, it is important to note that they are not scientific facts. They represent centuries of human tradition and personal belief systems that have grown around the natural beauty of these minerals.
Care and Cleaning
Proper care is crucial for maintaining the beauty and integrity of gemstone jewelry, and the requirements differ significantly for these three December birthstones due to their varying hardness and stability.
Turquoise requires the most diligent care. Its low hardness (5-6) and porous nature make it susceptible to damage. It should be protected from scratches, chemicals, and prolonged exposure to water, oils, and cosmetics, which can cause discoloration and dullness. Cleaning should be done with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals. It is best to put on turquoise jewelry last when dressing and remove it before activities like cleaning, swimming, or exercising.
Zircon, despite its good hardness, is brittle due to its cleavage. It should be protected from hard blows and extreme temperature changes, which can cause it to fracture. When cleaning, use warm water, a mild detergent, and a soft brush. It can be rinsed and dried with a lint-free cloth. As with most gems, avoid ultrasonic cleaners, especially if the stone has been fractured or has inclusions.
Tanzanite also has perfect cleavage, making it relatively fragile. It is prone to chipping and breaking if struck. It is not recommended for rings or bracelets that are subject to daily wear and tear; pendants and earrings are safer settings. Cleaning can be done with warm, soapy water and a soft brush. Avoid ultrasonic cleaners and sudden temperature changes, which can stress the stone. Given its relative softness compared to diamonds or sapphires, it should be stored separately to prevent scratching.
For all three gems, removing jewelry during physical activities, housework, and exposure to harsh environments is the best practice to ensure their longevity.
Conclusion
The December birthstones—tanzanite, turquoise, and zircon—offer a remarkable diversity within a single month. From the ancient, sky-blue turquoise cherished by Native American cultures to the fiery, diamond-like zircon found across the globe, and the recently discovered, violet-blue tanzanite from a single valley in Tanzania, each gem tells a unique story of geological formation and human history. Their varied properties, from turquoise's opacity and softness to zircon's brilliance and cleavage, and tanzanite's trichroism and fragility, necessitate different approaches to care and setting. Whether chosen for their symbolic meanings, historical significance, or sheer visual appeal, these three blue gems provide a rich palette of options for those born in December, connecting them to a legacy of beauty that spans from the ancient earth to modern jewelry design.