For those born in the final month of the year, December offers a unique and diverse selection of birthstones: turquoise, tanzanite, and zircon. Each of these gems presents a distinct shade of blue, from the earthy, opaque tones of turquoise to the vibrant, violet-blue of tanzanite and the brilliant, fiery sparkle of zircon. This trio reflects the varied landscapes and histories of their origins, providing a wide spectrum of choices for personal adornment and symbolic meaning. This article provides a comprehensive exploration of these three December birthstones, detailing their historical significance, geological origins, gemological properties, and practical care, drawing exclusively from established gemological sources.
History and Lore
The history of these December birthstones spans millennia and continents, with each stone carrying a unique narrative.
Turquoise: An Ancient Talisman
Turquoise is arguably one of the most ancient gemstones used as a talisman and decorative element. Archaeological evidence indicates that Native Americans in the Southwestern United States were using turquoise over 2000 years ago. These ancient artists crafted beads, pendants, inlay work, and small sculptures from the stone. Its importance persisted through the centuries, and turquoise is still an integral part of Southwestern culture today, often set into sterling silver jewelry. Its enduring appeal lies in its distinctive color and its perceived protective qualities.
Zircon: The Diamond Imitator and Beyond
Zircon has a long history of being mistaken for more valuable gemstones, particularly diamond, due to its exceptional brilliance and fire. For centuries, colorless zircon was used as a diamond simulant. However, its value as a gemstone in its own right has been recognized for much longer. The gem is celebrated for its high luster, and many specimens produce a colorful fire that is similar to diamond. This unique optical property, combined with its natural occurrence in a range of colors, has secured its place in the gemological world.
Tanzanite: A Modern Discovery
In stark contrast to the ancient histories of turquoise and zircon, tanzanite is a 20th-century discovery. It was first found in the Merelani Hills of Tanzania in 1967. Its vivid violet-blue color, a result of vanadium and chromium impurities in the mineral zoisite, was unlike any other blue gemstone on the market. This discovery led to its rapid popularity and its official addition to the modern birthstone list by the American Gem Trade Association in 2002, marking the first change to the official U.S. birthstone chart in 50 years.
The journey to official birthstone status for these gems is part of a longer evolution. The National Association of Jewelers (now Jewelers of America) established the first official birthstone chart in the United States, creating a standardized list that is still widely used. Over time, this list has been updated to include new discoveries and alternative options. For December, the modern chart has expanded from its traditional offerings, incorporating tanzanite and zircon alongside turquoise.
Geological Formation and Sources
The formation and mining locations of these three gems are as diverse as their appearances.
Turquoise: A Hydrated Mineral
Turquoise is not a silicate mineral like most gemstones but a hydrous phosphate of copper and aluminum. It forms in arid regions where acidic, copper-rich groundwater seeps through aluminum-bearing rocks, such as volcanic ash. The slow evaporation of this water leads to the deposition of turquoise in nodules or veins. While the Southwestern United States has historically been a significant source, major deposits are also found in Iran, Egypt, and China. Its formation process often results in an opaque stone, which is typically cut into cabochons.
Zircon: A Primary Zirconium Silicate
Zircon is a primary mineral, meaning it crystallizes directly from magma. It is one of the oldest minerals on Earth, with some crystals dating back billions of years. Zircon forms in igneous and metamorphic rocks. Commercial sources are found in several countries, including Australia (which produces most of the world's zircon), Sri Lanka, and parts of Asia. Its formation under high temperatures and pressures contributes to its durability and unique crystal structure.
Tanzanite: A Single-Source Gemstone
Tanzanite's geological story is exceptionally unique. It is found in only one location on Earth: the Merelani Hills near Mount Kilimanjaro in Tanzania. This gemstone is a variety of the mineral zoisite, which formed from the heating and alteration of rocks during a massive geological event millions of years ago. The specific conditions that created tanzanite are believed to be confined to a very small area, making it a truly single-source gemstone and adding to its rarity and allure.
Gemological Properties
Understanding the physical and chemical properties of a gemstone is crucial for its identification, valuation, and care. The following table summarizes the key gemological data for the three December birthstones, based on the provided sources.
| Gemstone | Chemical Composition | Hardness (Mohs Scale) | Typical Treatments | Key Optical Properties |
|---|---|---|---|---|
| Turquoise | Hydrous Copper Aluminum Phosphate | 5-6 (Low Hardness) | Stabilization, Dyeing | Opaque, waxy luster |
| Zircon | Zirconium Silicate (ZrSiO₄) | 6.5-7.5 | Heat treatment (for color) | High luster, strong birefringence, "fire" |
| Tanzanite | Calcium Aluminum Hydroxyl Silicate (Zoisite) | 6.5-7 | Heat treatment (standard) | Trichroic (shows three colors), pleochroism |
Turquoise
Turquoise is characterized by its opacity and typical blue to blue-green to yellowish green color. The most prized color is a bright, uniform blue. Its hardness ranges from 5 to 6 on the Mohs scale, making it relatively soft compared to other gemstones. This low hardness, combined with its porous nature, makes it susceptible to scratching and chemical damage. Most turquoise is treated to enhance its color and durability; a common method is stabilization, where the stone is impregnated with a clear resin or wax. Lab-created turquoise is also available for cost-conscious shoppers.
Zircon
Zircon is a gemstone of brilliance and fire. It has a high luster and, for colorless varieties, a dispersion (fire) higher than that of diamond. Its hardness of 6.5 to 7.5 on the Mohs scale makes it durable enough for most jewelry settings, though it can be brittle due to its tetragonal crystal structure. Zircon occurs in a variety of colors, including blue, yellow, green, brown, and red. Blue zircon, often a light sky blue, is the most popular color for December, typically achieved through heat treatment of brown zircon crystals.
Tanzanite
Tanzanite's most famous characteristic is its trichroism—the ability to show three different colors (violet-blue, blue, and burgundy) when viewed from different crystal directions. Its color ranges from ultramarine blue to violet. With a hardness of 6.5 to 7, it is moderately durable but can be susceptible to chipping if hit hard. Virtually all tanzanite on the market has been heat-treated to remove the brownish-orange hues of the raw zoisite and produce the desirable blue and violet colors. This treatment is stable and permanent, and it is considered a standard industry practice.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, these gemstones have been imbued with symbolic meaning and metaphysical properties throughout history.
- Turquoise has long been regarded as a stone of protection and healing. In many cultures, including those of Native Americans and ancient Persians, it was believed to ward off evil and bring good fortune. Its association with the sky and water links it to tranquility and peace. The Complete Birthstone Chart Reference Table notes its key symbolism as Protection, Healing, and Wisdom.
- Zircon is often associated with wisdom, honor, and purity. In some traditions, it is believed to promote spiritual growth and aid in sleep. Its fiery sparkle is said to inspire ambition and self-confidence.
- Tanzanite, as a modern discovery, has quickly acquired symbolic meaning. It is often called the "stone of transformation," believed to facilitate a higher consciousness, intuition, and spiritual perception. Its symbolism, as listed in the reference table, aligns with Protection, Healing, and Wisdom.
It is important to note that metaphysical beliefs are cultural and personal interpretations, not established scientific facts. They are included here as part of the rich cultural history surrounding these gems.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone jewelry. The properties outlined in the sources directly inform the recommended care methods.
Turquoise Care
Due to its low hardness (5-6) and porous nature, turquoise requires gentle handling. * Avoid Exposure: Keep turquoise away from chemicals, including perfumes, lotions, and household cleaners, as they can cause discoloration and damage the stone's surface. * Cleaning: Clean only with a soft, dry cloth. Avoid ultrasonic cleaners, steam cleaners, and even warm soapy water, which can penetrate the stone and affect any stabilizing treatments or the stone itself. * Storage: Store turquoise separately from other jewelry to prevent scratches.
Zircon Care
With a hardness of 6.5-7.5, zircon is relatively durable but can be brittle. * Avoid Hard Impacts: Due to its brittleness, avoid wearing zircon jewelry during strenuous activities where it might be struck. * Cleaning: Clean zircon with warm, soapy water and a soft brush. It is generally safe for ultrasonic cleaners, but caution is advised if the stone has any fractures. Avoid sudden temperature changes, which can cause cracking. * Storage: Store zircon separately to prevent scratching softer gems.
Tanzanite Care
Tanzanite's hardness of 6.5-7 makes it suitable for most jewelry, but its cleavage (a tendency to split along certain planes) requires care. * Protect from Impacts: Like zircon, tanzanite should be protected from hard blows. It is not recommended for rings worn daily on the hand due to the risk of impact. * Cleaning: The safest method is warm, soapy water with a soft brush. Avoid ultrasonic cleaners and steam, as the vibrations and heat can potentially damage the stone. * Storage: Store tanzanite jewelry in a soft cloth or padded box, separate from other pieces.
Conclusion
The three December birthstones—turquoise, tanzanite, and zircon—offer a remarkable diversity within a shared color palette. Turquoise connects us to ancient traditions and the earth, with its opaque, soothing hues. Zircon provides brilliant sparkle and fire, a gemstone with a long history of being prized for its beauty. Tanzanite represents modernity and rarity, a recent discovery that has captivated the world with its unique trichroic color. Each stone, with its distinct geological origin, gemological properties, and cultural significance, provides a meaningful choice for December birthdays. Whether selected for its historical lore, symbolic meaning, or simply its captivating beauty, any of these three gems serves as a timeless and personal talisman for the last month of the year.