A Guide to the Four Official Birthstones of December: Tanzanite, Turquoise, Zircon, and Blue Topaz

December holds a unique distinction in the calendar of birthstones. While most months are associated with a single gem, December boasts four officially recognized stones: Tanzanite, Turquoise, Zircon, and Blue Topaz. This abundance offers those born in the final month of the year a rich palette of colors, histories, and properties from which to choose. All four gems share a common thread of captivating blue hues, evoking the cool tones of winter skies and icy landscapes, yet each possesses a unique identity forged by geological processes, historical lore, and modern gemology.

The evolution of this list reflects both tradition and modernity. Historically, Turquoise and Zircon were the primary gems for December. The 20th century brought new discoveries and commercial interests, leading to the addition of Blue Topaz and, most recently, Tanzanite in 2002. This comprehensive guide explores the history, geological origins, gemological properties, and symbolic meanings of these four remarkable gemstones, providing an expert overview for enthusiasts, collectors, and anyone captivated by the beauty of December's birthstones.

History and Lore: A Journey Through Time

The tradition of assigning gemstones to specific months has ancient roots, with practices dating back to Mesopotamia and later adopted by Greek and Roman cultures. The December stones, in particular, have a history of evolution. Originally, only Turquoise and Zircon graced the list as December’s gems. The list expanded over time, reflecting the discovery of new deposits and the growing appreciation for these stones in the world of jewelry.

Turquoise is arguably the oldest of the four, with a history spanning thousands of years. It was revered by ancient civilizations, including the Egyptians, who adorned themselves with this sky-blue stone. The name "turquoise" itself is derived from the French phrase "pierre tourques," meaning "Turkish stone," as the gem was first brought to Europe from Turkey. It has long been associated with protection, good fortune, and spiritual grounding. Turquoise was often used in amulets and talismans, believed to ward off evil and bring peace to the wearer.

Zircon is another of the original December stones, with a history that is often confused due to its similarity in name and appearance to cubic zirconia, a synthetic diamond simulant. However, natural zircon is one of the oldest minerals on Earth, with deposits found that are billions of years old. For centuries, colorless zircon was mistaken for diamond due to its high brilliance and fire. Historically, zircon has been associated with wisdom, clarity, and wealth. It was believed to promote a restful sleep and protect travelers.

Blue Topaz, while not a traditional December stone, has become an integral part of the modern list. Its use in jewelry dates back to ancient times, but its popularity surged in the 20th century. The stone is known for its clear, crisp blue color, reminiscent of a winter sky. Its addition to the December list provided consumers with a more durable and affordable blue gemstone option.

Tanzanite is the most recent addition, officially recognized as a December birthstone in 2002. Its history is entirely modern. Discovered in the Merelani Hills of Northern Tanzania in 1967, this gem was introduced to the world by Tiffany & Co., who named it after its country of origin. Its rapid rise to prominence is a testament to its unique beauty and rarity. Tanzanite represents transformation and new beginnings, a fitting symbol for a gemstone that burst onto the scene in the latter half of the 20th century.

Geological Formation and Sources

Each of December's birthstones forms under unique geological conditions, resulting in distinct chemical compositions and physical properties. Their origins are concentrated in specific regions around the globe, making them geographically significant.

Turquoise is a hydrous phosphate of copper and aluminum. It forms in arid regions where acidic, copper-rich groundwater seeps through aluminum-bearing rocks. Over millions of years, this process creates deposits where the mineral combines with water to form turquoise. The finest quality turquoise comes from Iran, but significant sources also include the Southwestern United States (Arizona, New Mexico, Nevada), China, and Egypt. The stone's color, ranging from sky blue to greenish-blue, is directly influenced by the amount of copper (blue) or iron (green) present during its formation.

Zircon is a zirconium silicate and is a common mineral found in igneous and metamorphic rocks. It forms from magma as it cools and crystallizes. The blue variety of zircon, which is the most popular for December, is created by heating colorless or brownish zircon to high temperatures, a process that removes the impurities causing the original color. Major sources for zircon include Cambodia, Sri Lanka, Thailand, and Australia. The stone is known for its exceptional brilliance and fire, which rivals that of a diamond.

Tanzanite is a variety of the mineral zoisite and owes its existence to a unique geological event. It is found in only one place in the world: the Merelani Hills of Northern Tanzania, near the base of Mount Kilimanjaro. The gem formed approximately 585 million years ago when tectonic plates shifted, causing intense heat and pressure that transformed the existing zoisite crystals, introducing the elements (vanadium and chromium) responsible for its signature blue-violet color. Its singular source location makes it at least a thousand times rarer than diamond.

Blue Topaz is a silicate mineral of aluminum and fluorine. It forms in igneous rocks, particularly in the final stages of magma crystallization. While topaz occurs naturally in a variety of colors, the vibrant blue seen in most jewelry is often the result of irradiation and heat treatment of colorless topaz. The primary sources of topaz are Brazil, but it is also found in Nigeria, Sri Lanka, and Pakistan.

Gemological Properties

The physical and optical characteristics of these gemstones dictate their durability, brilliance, and suitability for jewelry. Understanding these properties is essential for both jewelers and consumers.

Chemical Composition and Hardness

The four stones differ significantly in their hardness on the Mohs scale, a critical factor for their care and wearability.

Zircon is the hardest of the group, with a Mohs hardness of 6.5 to 7.5. Its chemical formula is ZrSiO₄. While relatively durable, it is brittle and can be prone to chipping if knocked against a hard surface.
Blue Topaz has a Mohs hardness of 8, making it quite durable and resistant to scratching. Its chemical formula is Al₂(F,OH)₂SiO₄.
Tanzanite has a Mohs hardness of 6.5 to 7. It is a member of the zoisite family, with a chemical formula of Ca₂Al₃(SiO₄)₃(OH). It possesses perfect cleavage in one direction, meaning it can split easily if struck with force, requiring protective settings for jewelry.
Turquoise is the softest and most porous of the four, with a Mohs hardness of 5 to 6. Its chemical formula is a hydrated phosphate of copper and aluminum, CuAl₆(PO₄)₄(OH)₈·4H₂O. Its porosity makes it susceptible to absorbing oils and chemicals, which can alter its color over time.

Color and Clarity

The defining feature of December's birthstones is their blue coloration, though the specific shades and optical effects vary widely.

Turquoise is prized for its distinctive "egg blue" to greenish-blue color, often exhibiting a host rock matrix in the form of dark veins or webbing, which is considered part of its character.
Zircon is known for its exceptional brilliance and fire. The blue variety is typically a bright, clear, and intense blue. Colorless zircon was historically used as a diamond substitute.
Tanzanite is renowned for its rich, saturated blue with a distinct violet undertone. It is strongly trichroic, meaning it can display three different colors (blue, violet, and reddish-brown) when viewed from different crystal directions. This pleochroism is a key identifier.
Blue Topaz ranges from a pale, sky blue to a deep, saturated "Swiss Blue" or "London Blue." The clarity is typically high, with eye-clean stones being common.

Comparative Properties Table

Gemstone	Mohs Hardness	Chemical Composition	Key Color	Typical Treatments
Turquoise	5 - 6	CuAl₆(PO₄)₄(OH)₈·4H₂O	Sky blue to greenish-blue	Stabilization, dyeing
Tanzanite	6.5 - 7	Ca₂Al₃(SiO₄)₃(OH)	Blue-violet	Heating (to remove brown tones)
Zircon	6.5 - 7.5	ZrSiO₄	Bright blue (heat-treated)	Heating (for color)
Blue Topaz	8	Al₂(F,OH)₂SiO₄	Pale to deep blue	Irradiation, heating

Symbolism and Metaphysical Beliefs

Beyond their physical beauty, December's birthstones are deeply imbued with symbolic meaning and metaphysical properties, cherished for their perceived ability to influence the mind, body, and spirit.

Turquoise is widely regarded as a stone of protection, grounding, and healing. It is believed to act as a steadying force, providing a sense of calm and peace, especially when life feels chaotic. Many cultures have viewed it as a good-luck charm, a guardian against negative energy, and a conduit for spiritual attunement. It is also associated with the immune system and is said to support detoxification.

Tanzanite is a stone of transformation, linked to new beginnings, spiritual growth, and heightened intuition. Its unique blue-violet hue is said to foster compassion, calmness, and a deeper understanding of oneself. It is believed to open the mind to new possibilities and encourage a positive outlook on life. Some sources also suggest it has properties that can improve skin and hair health.

Zircon is associated with clarity, wisdom, and prosperity. It is believed to sharpen focus, enhance mental clarity, and promote wise decision-making. Zircon is also thought to attract wealth and success while protecting the wearer during travel. For those seeking a restful night, zircon is often turned to for its supposed ability to ward off nightmares and encourage peaceful sleep.

Blue Topaz, while its metaphysical properties are less extensively documented in the provided sources compared to the others, is generally associated with calmness, clarity, and communication. Its cool blue color is linked to soothing energies, helping to reduce stress and promote clear, honest expression.

Care and Cleaning

Proper care is paramount to maintaining the beauty and longevity of any gemstone jewelry. Due to their differing properties, each of December's stones requires specific attention.

Turquoise: As the most delicate of the four, turquoise requires gentle handling. It is porous and can be damaged by chemicals, including those found in cosmetics, lotions, and even some soaps. Clean it only with warm, soapy water and a soft cloth. Avoid ultrasonic cleaners and steam cleaners. Store it separately to prevent scratching.

Tanzanite: With its good hardness but perfect cleavage, tanzanite is fragile. It should not be subjected to rough wear or sudden temperature changes. The safest method for cleaning is warm, soapy water and a soft brush. Ultrasonic and steam cleaners are not recommended as they can cause the stone to fracture.

Zircon: Although relatively hard, zircon is brittle. It can be damaged by a sharp blow, so settings should protect the stone from impact. Cleaning can be done with warm, soapy water and a soft brush. While generally stable, some zircon may be sensitive to light, but this is rarely a concern with the blue, heat-treated varieties used in jewelry.

Blue Topaz: As the most durable of the group with a hardness of 8, blue topaz is well-suited for everyday wear. It can be safely cleaned with warm, soapy water and a soft brush. It is also generally safe to use an ultrasonic cleaner, though caution is always advised. However, prolonged exposure to strong heat or sunlight could potentially cause fading in some treated stones, though this is uncommon.

Conclusion

December's birthstones offer a remarkable diversity that sets them apart from all other months. The selection of Tanzanite, Turquoise, Zircon, and Blue Topaz provides a spectrum of blues, from the soft sky tones of turquoise to the deep, violet-tinged hues of tanzanite. Each stone carries a unique narrative—from the ancient protective legends of turquoise and the ancient wisdom of zircon to the modern discovery of tanzanite and the commercial appeal of blue topaz.

For those born in December, the choice is not limited to a single gem but extends to a collection of stones, each with its own geological story, symbolic power, and aesthetic appeal. Whether chosen for its historical significance, its metaphysical properties, or simply its stunning color, any of these four gems serves as a beautiful and meaningful emblem for the final month of the year. Their enduring beauty and rich heritage ensure that they will continue to be cherished for generations to come.