The month of December is uniquely associated with four distinct gemstones: Topaz, Tanzanite, Zircon, and Turquoise. This multiplicity offers a fascinating study in the evolution of birthstone traditions, from ancient historical lists to modern standardized charts. While each stone possesses its own unique geological story and aesthetic appeal, they are all united by their designation as the birthstone for the twelfth month of the year. This article explores the history, properties, and significance of these December birthstones, drawing upon the rich tapestry of information available from gemological and historical sources.
History and Lore: The Evolution of December's Gems
The concept of a single birthstone per month is a relatively modern development. Historically, birthstones were linked to the twelve stones on the breastplate of the High Priest of ancient Israel, as described in the Book of Exodus. However, the specific stones assigned to each month have shifted over centuries, influenced by trade, availability, and cultural preferences.
The modern list of birthstones was largely standardized in 1912 by the American National Association of Jewelers (now Jewelers of America), with subsequent updates. The December birthstone list has seen particular evolution. Initially, Turquoise was the primary stone associated with December, valued for millennia across cultures from ancient Egypt to Persia and the American Southwest. Its vibrant blue-green hues have long been associated with protection, wisdom, and tranquility.
In the 20th century, Blue Topaz gained prominence as a December birthstone, especially in North America. Topaz, a silicate mineral, occurs in a wide range of colors, but the brilliant blue variety became commercially popular due to its clarity and affordability. Its association with December is often linked to its historical use in jewelry, particularly during the Art Deco period of the 1920s and 1930s, where its cool blue tones complemented the era's geometric designs. As noted in one source, "topaz jewellery reached its peak in the 18th and early 19th centuries," and the "postwar Art Deco period" saw a resurgence in its popularity.
Tanzanite, a relatively recent discovery, was added to the December list by the Jewelry Industry Council of America in 2002. Found only in the Merelani Hills of Tanzania, this vivid blue to violet gemstone was first identified in 1967. Its inclusion reflects a modern adaptation of birthstone lists to incorporate newly discovered and significant gemological materials.
Blue Zircon is the December birthstone listed in the traditional British and European lists. Zircon is one of the oldest minerals on Earth, with formations dating back billions of years. Historically, zircon was mistaken for diamond due to its high brilliance and dispersion. The blue variety, often achieved through heat treatment of brown zircon, is prized for its "unusually bright lustre and high dispersion, rivalling that of diamond."
The inclusion of multiple stones for December allows for personal preference and cultural context. For instance, the modern U.S. list includes Blue Topaz as the primary stone, with Tanzanite and Zircon as alternatives. This reflects a trend toward offering consumers a wider range of choices in color and price point.
Geological Formation and Sources
Understanding the origins of these gems reveals their distinct journeys from the Earth's interior to our jewelry boxes.
Topaz is a silicate mineral of aluminum and fluorine, crystallizing in igneous rocks like granite and rhyolite. Major sources include Brazil, which is the world's leading producer of topaz, particularly for blue varieties. Other significant sources are Sri Lanka, Nigeria, and the United States (notably in Texas and Utah). The blue color in most commercial topaz is the result of irradiation and heat treatment, a standard industry practice that enhances the stone's natural pale blue to a more saturated hue.
Tanzanite is a variety of the mineral zoisite and owes its existence to a unique geological event. It formed approximately 585 million years ago when the tectonic plates of East Africa were colliding, creating intense heat and pressure that transformed the host rock. It is found exclusively in a single, small mining area in the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. This extreme rarity is a key factor in its value and allure.
Zircon (not to be confused with synthetic cubic zirconia) is a zirconium silicate mineral. It forms in a variety of rock types, including granite, gneiss, and metamorphic rocks. Natural zircon occurs in many colors, but blue is among the most sought-after for jewelry. The blue color in zircon is typically the result of heat treatment applied to brown zircon crystals. Major sources for gem-quality zircon include Cambodia, Sri Lanka, Thailand, and Australia. Zircon is notably the oldest mineral on Earth, with some crystals dating back 4.4 billion years.
Turquoise is a hydrated phosphate of copper and aluminum. Its formation requires a specific combination of copper-rich groundwater percolating through rocks containing aluminum and phosphorus. This process occurs in arid regions, leading to the formation of nodules or veins in the host rock. The most famous sources are in the American Southwest (Arizona, New Mexico, Nevada), Iran (historically the source of the finest "Persian turquoise"), and China. The color, which ranges from sky blue to green, is directly influenced by the presence of copper (blue) and iron (green).
Gemological Properties
The four December birthstones differ significantly in their physical and chemical properties, which affect their durability, care, and suitability for different types of jewelry.
| Property | Topaz (Blue) | Tanzanite | Zircon (Blue) | Turquoise |
|---|---|---|---|---|
| Chemical Formula | Al₂SiO₄(F,OH)₂ | Ca₂Al₃(SiO₄)₃(OH) | ZrSiO₄ | CuAl₆(PO₄)₄(OH)₈·4H₂O |
| Crystal System | Orthorhombic | Orthorhombic | Tetragonal | Triclinic |
| Hardness (Mohs) | 8 | 6.5 - 7 | 6.5 - 7.5 | 5 - 6 |
| Specific Gravity | 3.49 - 3.57 | 3.35 | 4.6 - 4.7 | 2.6 - 2.9 |
| Refractive Index | 1.609 - 1.627 | 1.691 - 1.700 | 1.92 - 2.01 | 1.61 - 1.65 |
| Luster | Vitreous | Vitreous to Greasy | Adamantine to Vitreous | Waxy to Vitreous |
| Durability | Very Good | Fair to Good | Good | Fair to Poor (porous) |
| Key Treatments | Irradiation, Heat | Heat (to remove brown tones) | Heat (for color) | Stabilization (common) |
Topaz is a relatively hard and durable gemstone, ranking 8 on the Mohs scale. This makes it suitable for all types of jewelry, including rings and bracelets that may experience daily wear. Its vitreous luster and excellent clarity contribute to its brilliance. The most prized blue topaz shades include Swiss Blue (a bright, medium blue), Sky Blue (a lighter, pastel blue), and London Blue (a deep, saturated blue-green). The deep blue of London Blue topaz is achieved through a combination of irradiation and heat treatment, starting from a pale brown or colorless crystal.
Tanzanite is softer than topaz, with a hardness of 6.5 to 7 on the Mohs scale. While durable enough for earrings and pendants, it is less suitable for rings or bracelets unless set in protective settings and worn with care. Its defining characteristic is its strong trichroism, displaying three different colors: blue, violet, and burgundy. The most valuable tanzanite shows a vivid violet-blue hue. Like many colored stones, tanzanite is almost always heat-treated to remove the brownish tones and enhance its blue-violet color. This treatment is permanent and is considered standard practice in the gem trade.
Zircon is notable for its high refractive index and strong dispersion, giving it a brilliance that can rival diamond. With a hardness of 6.5 to 7.5, it is reasonably durable but can be brittle due to its crystal structure. Blue zircon is typically produced by heating brown zircon crystals to high temperatures, which can create a permanent blue color. However, some blue zircon may fade if exposed to prolonged high heat or strong light, so care should be taken. Zircon is often used as a diamond simulant due to its optical properties, but it is a distinct and valuable gem in its own right.
Turquoise is the softest and most porous of the four December stones, with a hardness of 5 to 6. This makes it susceptible to scratching, chipping, and chemical damage. Its porous nature means it can absorb oils, lotions, and perfumes, which can darken or stain the stone over time. To enhance durability and color consistency, most turquoise used in jewelry is "stabilized" – a process where the stone is impregnated with a clear resin or polymer. Natural, untreated turquoise is rarer and often commands a premium, especially for high-grade specimens with even color and minimal matrix (the host rock veins). The most prized turquoise is a uniform, robin's egg blue, historically associated with Persian mines.
Symbolism and Metaphysical Beliefs
Each of the December birthstones carries a rich legacy of symbolism and metaphysical beliefs, often tied to its color and historical lore.
Topaz has long been associated with warmth, clarity, and communication. In ancient times, it was believed to have cooling properties, both physically and emotionally. Some traditions hold that topaz can promote truth, forgiveness, and mental clarity. The blue variety, in particular, is linked to the throat chakra, thought to aid in honest communication and self-expression. It is also considered a stone of friendship and love, often given as a token of affection.
Tanzanite, as a modern gem, has quickly developed its own symbolic meanings. It is often called the "stone of transformation," believed to facilitate spiritual awakening and higher consciousness. Its striking blue-violet color is associated with the crown and third-eye chakras, promoting intuition and psychic abilities. Some believe tanzanite can help in overcoming grief and loss, encouraging a forward-looking perspective. Its rarity is also symbolic of individuality and uniqueness.
Zircon is one of the oldest birthstones, carrying ancient symbolism. It is traditionally associated with wisdom, honor, and purity. In medieval times, zircon was believed to promote rest and ward off evil spirits. Blue zircon, in particular, is thought to enhance spiritual growth and attract prosperity. Its high dispersion and brilliance are linked to mental clarity and the ability to see the truth in situations. Zircon is also considered a stone of grounding, helping to connect the physical and spiritual realms.
Turquoise is perhaps the most culturally diverse in its symbolism. For Native American tribes, particularly in the Southwest, turquoise is a sacred stone representing the sky, water, and earth. It is believed to offer protection, health, and good fortune. In many cultures, turquoise is seen as a stone of peace, communication, and emotional balance. It is said to absorb negative energy and protect the wearer from harm. The color change of turquoise (from blue to green) is sometimes interpreted as reflecting the wearer's health and emotional state.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of December birthstones, given their varying hardness and porosity.
Topaz is relatively easy to care for due to its high hardness. It can be cleaned with warm water, mild soap, and a soft brush. Avoid ultrasonic cleaners and steam cleaning, as sudden temperature changes can cause fractures, especially in stones that have been treated. Store topaz jewelry separately to prevent scratching by harder stones.
Tanzanite requires gentle handling due to its moderate hardness and potential for cleavage. Clean it with a soft cloth, warm water, and a mild detergent. Avoid ultrasonic cleaners and steam, as vibrations and heat can damage the stone. It is best to remove tanzanite jewelry before physical activities to prevent impact.
Zircon is relatively durable but can be brittle. Clean it with a soft brush, warm water, and mild soap. Avoid ultrasonic cleaners and sudden temperature changes, which can cause the stone to crack. Due to its high refractive index, zircon can show off its brilliance when clean, so regular gentle cleaning is recommended.
Turquoise is the most delicate and requires the most careful maintenance. It should be wiped with a soft, dry cloth after wear to remove oils and sweat. Avoid exposure to chemicals, including perfumes, lotions, and household cleaners, as they can damage the stone. Do not soak turquoise in water, especially if it is not stabilized, as it can absorb water and become discolored or weakened. Store turquoise jewelry in a soft pouch, away from other jewelry to prevent scratching.
Conclusion
The December birthstones—Topaz, Tanzanite, Zircon, and Turquoise—offer a remarkable diversity in color, history, and meaning. From the ancient, protective allure of turquoise to the modern, transformative energy of tanzanite, each stone provides a unique connection to the natural world and human culture. Their varying gemological properties dictate different care requirements, making it important for owners to understand the specific needs of their chosen gem. Whether chosen for their birth month, aesthetic appeal, or symbolic significance, these stones continue to captivate gem enthusiasts and jewelry lovers alike, each holding a distinct place in the pantheon of precious gems.