December is unique in the birthstone calendar, offering not one, but three distinct gemstones to represent those born in the final month of the year: tanzanite, turquoise, and zircon. Each of these stones possesses a captivating blue hue, yet they differ dramatically in their origins, properties, and histories. From the ancient earth of the American Southwest to the volcanic landscapes of Tanzania and the deep geologic formations of Australia, these gems tell a story of cultural significance, scientific wonder, and modern gemology. This article explores the geological formation, gemological properties, historical lore, and practical care of these three December birthstones, providing a comprehensive guide for enthusiasts, collectors, and jewelry buyers.
History and Lore
The history of December’s birthstones is a tapestry woven from ancient traditions and modern additions. The most established of the three, turquoise, has been revered for millennia. In the southwestern United States, Native Americans were using turquoise over 2000 years ago, creating beads, pendants, inlay work, and small sculptures. This ancient artistry solidified turquoise’s role as a vital element of Southwestern culture, a tradition that continues to this day. Historically, turquoise has been a symbol of protection, health, and good fortune across many cultures, from ancient Egypt to Persia.
Zircon, the other traditional December stone, has a long and sometimes misunderstood history. For centuries, it was prized for its brilliance and fire, which are so similar to diamond that it was often used as a diamond alternative. Its high luster and colorful fire made it a popular gem in medieval Europe. However, its reputation was somewhat tarnished in the 20th century when cubic zirconia, a synthetic diamond simulant, became widely available, leading to public confusion between the natural gemstone zircon and the lab-created material.
Tanzanite is the newest addition to the December birthstone family. It was officially added by the American Gem Trade Association in 2002, marking the first change to the birthstone list in 50 years. Discovered in the late 1960s in a single small area of Tanzania, this gem’s vibrant blue-to-violet color immediately captivated the jewelry world. Its rapid rise from a geological curiosity to a globally recognized birthstone is a testament to its unique beauty and the marketing power of a well-known brand.
The modern birthstone list for December was also updated in 1952, a year that saw significant changes to the official charts. At that time, zircon replaced lapis lazuli as a modern birthstone, and blue topaz was also introduced. The evolution of the birthstone chart reflects a blend of historical tradition and contemporary availability, ensuring that those born in December have a range of options to suit their style and budget.
Geological Formation and Sources
Understanding the origins of these gems reveals the diverse geological processes that create such beauty.
Turquoise is a secondary mineral, meaning it forms near the earth’s surface through the interaction of water with pre-existing rocks. It is a hydrous phosphate of copper and aluminum. The most prized blue colors come from copper, while green hues are influenced by iron. Major sources include the southwestern United States (Arizona, New Mexico, Nevada), Iran, and Tibet. The material is often found in nodules or veins within host rock, which is why it is typically cut into cabochons or used in mosaic work rather than faceted.
Zircon is a primary mineral, a zirconium silicate (ZrSiO₄) that crystallizes from magma as it cools. It is one of the oldest minerals on Earth, with some crystals dating back billions of years. Zircon is found in many igneous and metamorphic rocks worldwide. However, the gem-quality crystals used in jewelry are primarily mined from placer deposits in countries like Australia, Cambodia, Sri Lanka, and Thailand. Australia is particularly known for its production of brownish zircons, which are often heat-treated to produce the popular blue color.
Tanzanite is a variety of the mineral zoisite. Its formation is exceptionally rare, believed to have occurred under specific geological conditions approximately 585 million years ago. It is found in only one place on Earth: the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. The gem forms from the metamorphism of limestone by heat and pressure from tectonic activity. Its scarcity is a direct result of this limited geographic occurrence, making it a truly exclusive gemstone.
Gemological Properties
While all three gems are associated with the color blue, their physical and chemical properties differ significantly, which directly impacts their durability, care, and value.
Turquoise is an opaque, non-crystalline mineral. Its hardness on the Mohs scale is relatively low, ranging from 5 to 6, making it susceptible to scratching. It has no cleavage, but its porous nature means it can absorb liquids and chemicals, which may alter its color. Turquoise is often stabilized with wax or resin to enhance its durability and color. Its chemical formula is a hydrated copper aluminum phosphate.
Zircon is a hard and durable gemstone, with a Mohs hardness of 6.5 to 7.5. It has a high refractive index, which gives it exceptional brilliance and fire, rivaling that of diamond. Zircon exhibits strong birefringence (double refraction), which can be observed under magnification. While natural zircons can be yellow, red, or brown, the blue zircon commonly seen in jewelry is almost always the result of heat treatment, which can also lighten or remove undesirable brown tones. Approximately 80% of the zircons sold today are blue, a color achieved through this process.
Tanzanite is a variety of zoisite with a Mohs hardness of 6.5 to 7, making it relatively durable for a colored gemstone, but still more susceptible to damage than harder stones like sapphire. It has perfect cleavage in one direction, meaning it can split easily if struck with force. Its most famous characteristic is its strong trichroism, displaying three different colors—blue, violet, and burgundy—depending on the viewing angle. Most tanzanite sold in jewelry today has been heat-treated to a stable blue to bluish-violet color, as the natural brownish hues are less desirable.
The following table summarizes the key gemological properties of the three December birthstones:
| Gemstone | Chemical Composition | Mohs Hardness | Crystal System | Key Optical Property | Common Treatments |
|---|---|---|---|---|---|
| Turquoise | CuAl₆(PO₄)₄(OH)₈·4H₂O | 5 - 6 | Triclinic (amorphous) | Opaque, waxy luster | Stabilization (wax/resin) |
| Zircon | ZrSiO₄ | 6.5 - 7.5 | Tetragonal | High refractive index, strong birefringence | Heat treatment (for color) |
| Tanzanite | Ca₂Al₃(SiO₄)₃(OH) | 6.5 - 7 | Orthorhombic | Trichroism (blue, violet, burgundy) | Heat treatment (to blue) |
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, each of these gemstones carries a rich legacy of symbolism and metaphysical belief.
Turquoise has long been considered a protective talisman. In many cultures, it is believed to ward off negative energy and bring good fortune. It is often associated with healing, balance, and tranquility. Native American tribes, in particular, view turquoise as a sacred stone, representing the sky and water, and it is frequently used in ceremonial jewelry.
Zircon, historically mistaken for diamond, inherited many of diamond’s symbolic associations. It is thought to promote honor, purity, and wisdom. Blue zircon, in particular, is associated with peace and tranquility. Some beliefs hold that zircon can aid in sleep and bring prosperity to its wearer.
Tanzanite, as a modern discovery, has quickly accumulated its own set of metaphysical meanings. It is often called the “stone of transformation,” believed to facilitate spiritual awakening and higher consciousness. Its striking color is said to stimulate the throat and brow chakras, enhancing communication and intuition. Some also associate it with calm and stress relief.
Care and Cleaning
The different physical properties of these gems dictate specific care instructions to ensure their longevity.
Turquoise requires gentle handling due to its low hardness and porosity. It should be cleaned with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals, as these can damage the stone or remove any stabilizing treatments. Store turquoise jewelry separately to prevent scratching by harder gems.
Zircon is relatively durable but can be brittle due to its perfect cleavage. It is safe to clean with warm soapy water and a soft brush. However, avoid sudden temperature changes, as zircon can fracture under thermal shock. Ultrasonic cleaners are generally not recommended. Its hardness makes it resistant to everyday wear, but it should still be stored carefully.
Tanzanite, with its perfect cleavage, is the most delicate of the three. It is unsuitable for rings or bracelets that are subject to hard knocks. It should be cleaned only with warm, soapy water and a soft cloth. Never use ultrasonic or steam cleaners, and avoid exposing it to rapid temperature changes. When setting tanzanite, jewelers often use protective settings like bezels to minimize the risk of damage.
Conclusion
The December birthstones—tanzanite, turquoise, and zircon—offer a diverse palette of blue hues, each with a unique story. Turquoise connects us to ancient cultures and the earth, with its opaque, soothing color and protective lore. Zircon, with its diamond-like brilliance and fiery sparkle, has a long history as a gem of honor and wisdom, its modern blue variety a product of both geology and human ingenuity. Tanzanite, the newest and most geographically confined of the trio, represents the cutting edge of gemology, its vibrant color and transformative symbolism capturing the modern imagination.
For those born in December, the choice between these three gems is a personal one, influenced by desired color, budget, durability, and the symbolic meaning that resonates most strongly. Whether drawn to the ancient heritage of turquoise, the classic fire of zircon, or the modern allure of tanzanite, December’s birthstones provide a beautiful and meaningful connection to the natural world and its timeless treasures.