The month of December is uniquely represented by three distinct birthstones: Turquoise, Zircon, and Tanzanite. Each offers a different interpretation of the color blue, allowing individuals born in the final month of the year a choice that aligns with their personal style and preferences. These gems possess rich histories, unique geological origins, and specific gemological properties that set them apart. Turquoise, with its ancient cultural significance and opaque beauty; Zircon, prized for its brilliance and historical use as a diamond simulant; and Tanzanite, the newest addition with its captivating color-change phenomenon. This article explores the history, formation, properties, and care of these three celebrated birthstones, providing a comprehensive guide for gemstone enthusiasts, jewelry buyers, and students of gemology.
History and Lore
The tradition of birthstones dates back centuries, with roots in the Breastplate of Aaron described in the Old Testament, which featured twelve gemstones representing the twelve tribes of Israel. Over time, this concept evolved, and by the 18th century, lists of birthstones by month were common in Europe. The modern list of birthstones, however, was standardized in the United States. The National Association of Jewelers released the first modern birthstone list in 1912, which replaced opaque traditional stones like bloodstone and sardonyx with clearer gems. This list has been updated several times to reflect market trends and availability, with the most recent additions in 2002 and 2016.
Turquoise is one of the oldest gemstones used by humans. In the southwestern United States, Native Americans were using turquoise over 2000 years ago. Ancient artists there produced beads, pendants, inlay work, and small sculptures. Turquoise remains an important part of Southwestern culture. The stone is also significant in other cultures; for example, it is believed to have been cherished by ancient Egyptians, Persians, and Chinese. Its name is derived from the French "pierre tourquoise," meaning "Turkish stone," likely because the stone was first brought to Europe from Turkey.
Zircon has a long and sometimes misunderstood history. Due to its high luster and refractive index, it was once used as an alternative to diamonds, a role that led to confusion with the synthetic material cubic zirconia, which is not related to natural zircon. The gem has been known since medieval times, and its name is derived from the Persian "zargun," meaning "gold-colored." Zircon was added to most birthstone lists in 1952, replacing lapis lazuli as a modern birthstone for December. At that time, topaz was a relatively costly gem, but the discovery of large deposits in Brazil greatly reduced the price of topaz, influencing birthstone lists.
Tanzanite is the newest birthstone for December, added to the list in 2002. Its history is remarkably short. The gem was first discovered in 1967 in the Merelani Hills of Tanzania, near Mount Kilimanjaro. Initially mistaken for sapphire, it was later identified as a variety of the mineral zoisite. The stone was renamed "tanzanite" by Tiffany & Co. in 1968, which launched a major marketing campaign that rapidly increased its popularity. Its unique color and limited geographic source have made it a coveted gem in a short time.
Geological Formation and Sources
Each of the December birthstones forms under different geological conditions and is mined in specific regions of the world.
Turquoise is a hydrous phosphate of copper and aluminum, forming in arid regions where acidic, copper-rich groundwater interacts with aluminum-bearing minerals. This process occurs in the near-surface environments of dry climates. The southwestern United States is a significant source of turquoise, with notable deposits in Arizona, Nevada, and New Mexico. The stone is also mined in Iran (historically the source of the finest "Persian turquoise"), China, and Afghanistan. The color of turquoise is directly influenced by its copper content; higher copper levels yield a more intense blue.
Zircon is a zirconium silicate (ZrSiO₄) that crystallizes from magma in igneous rocks like granite and syenite. It is also found in metamorphic rocks and as a detrital mineral in sedimentary deposits. Zircon is extremely durable and resistant to weathering, which is why it is often found in placer deposits (sands and gravels). The primary sources of gem-quality zircon include Australia (which produces most of the world's blue zircon), Sri Lanka, Myanmar, and Cambodia. Australia's zircon deposits are often associated with heavy mineral sands.
Tanzanite is a variety of the mineral zoisite, with its blue-to-violet color resulting from the presence of vanadium and heat treatment. It forms in the metamorphic rocks of the Merelani Hills in Tanzania, which is currently the only known source of gem-quality tanzanite in the world. The gem is found in a very small mining area, about 4 kilometers long and 2 kilometers wide, making it rarer than diamond. The stone is typically extracted from alluvial deposits where weathering has released the crystals from their host rock.
Gemological Properties
Understanding the physical and optical properties of these gemstones is essential for identification, valuation, and care.
| Property | Turquoise | Zircon | Tanzanite |
|---|---|---|---|
| Chemical Formula | CuAl₆(PO₄)₄(OH)₈·4H₂O | ZrSiO₄ | Ca₂Al₃(SiO₄)₃(OH) |
| Crystal System | Triclinic | Tetragonal | Orthorhombic |
| Hardness (Mohs) | 5 - 6 | 6.5 - 7.5 | 6 - 7 |
| Refractive Index | 1.610 - 1.650 | 1.925 - 2.015 | 1.691 - 1.700 |
| Specific Gravity | 2.60 - 2.90 | 4.60 - 4.70 | 3.35 |
| Luster | Waxy to subvitreous | Adamantine (brilliant) | Vitreous |
| Transparency | Opaque | Transparent to translucent | Transparent |
| Color Range | Blue to blue-green to yellowish green | Blue is most popular; also yellow, red, brown, white | Blue to bluish violet, often with pleochroism (color change) |
Turquoise is almost always opaque and is valued for its uniform color. Its hardness is relatively low, making it susceptible to scratching. It has a waxy to subvitreous luster and is often cut into cabochons, especially freeform shapes to maximize the rough. The most prized color is a bright, even blue.
Zircon is one of the few gemstones that can rival the brilliance of a diamond due to its high refractive index and strong dispersion (fire). It is typically transparent and is cut into faceted shapes like rounds, ovals, and cushions. Natural zircon is commonly yellow, red, or brown. Most blue zircon on the market today (approximately 80%) is the result of heat treatment, which transforms the original brown or yellow crystals into a desirable blue hue. Zircon is also known for its high birefringence, which can sometimes be visible under magnification.
Tanzanite is known for its strong pleochroism, meaning it displays different colors when viewed from different crystallographic directions. The most prized color is a vivid violet-blue. Virtually all tanzanite sold in jewelry is heat-treated to achieve its stable blue to violet-blue color; untreated crystals are often brownish. The stone is typically cut into calibrated shapes for jewelry and can be faceted or carved. Its hardness of 6 to 7 is adequate for jewelry but requires care.
Symbolism and Metaphysical Beliefs
Gemstones have long been attributed with symbolic meanings and healing powers, a tradition that continues today.
Turquoise is often called the "stone of the sky" and is believed to be a protective amulet. Historically, it was thought to change color to warn its owner of danger or illness. It is associated with wisdom, tranquility, and good fortune. In many cultures, it is believed to balance energies and promote emotional stability.
Zircon is said to bring prosperity and honor to its wearer. It is also believed to promote spiritual growth and help with grounding. Blue zircon, in particular, is associated with peace and tranquility. Some traditions hold that zircon can help relieve pain and aid in sleep.
Tanzanite is a relatively new stone in the metaphysical realm but has quickly gained a following. It is often called the "stone of transformation" and is believed to facilitate higher consciousness and spiritual awareness. It is associated with calmness, clarity, and the ability to see beyond the mundane. Some believe it can help overcome grief and stimulate the throat and third eye chakras.
It is important to note that while these beliefs are part of the cultural lore surrounding gemstones, they are not scientifically verified. They represent a rich tapestry of human history and belief systems.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone jewelry. The physical properties of each December birthstone dictate specific care instructions.
Turquoise is the most delicate of the three due to its porosity and lower hardness. It is susceptible to chemicals, including those found in cosmetics, hairspray, and even perspiration. These can cause discoloration or damage to the stone's surface. To clean turquoise, use only a soft, damp cloth. Avoid ultrasonic cleaners, steam cleaners, and harsh chemicals. Store it separately to prevent scratches from harder materials.
Zircon is relatively durable due to its hardness, but it can be brittle and prone to chipping if struck. It is generally safe to clean with warm soapy water and a soft brush. Avoid sudden temperature changes, as zircon can be sensitive to heat shocks. While it can withstand the ultrasonic cleaner, it is safer to use it with caution, especially if the stone has inclusions.
Tanzanite has a moderate hardness but is brittle due to its perfect cleavage in one direction. It should be protected from sharp blows and pressure. Cleaning should be done with warm soapy water and a soft brush. Ultrasonic cleaners and steam cleaners are not recommended, as the vibrations and heat can cause the stone to crack or cleave. It is best to remove tanzanite jewelry during physical activities.
For all three stones, it is advisable to remove jewelry before swimming, bathing, or engaging in activities that may expose them to harsh chemicals or physical impact. Regular inspections by a professional jeweler can help ensure settings remain secure and stones are in good condition.
Conclusion
The December birthstones—Turquoise, Zircon, and Tanzanite—offer a diverse selection for those born in the last month of the year. Turquoise carries the weight of ancient history and cultural significance, with its opaque, sky-blue beauty. Zircon provides brilliant sparkle and a wide range of colors, most famously the treated blue that replaced lapis lazuli in the modern birthstone list. Tanzanite, the newest member, captivates with its unique color-change properties and exclusive source in Tanzania. Each stone has distinct geological origins, gemological properties, and care requirements. Understanding these characteristics allows buyers to make informed choices and enthusiasts to appreciate the unique qualities of these remarkable gems. Whether chosen for their historical lore, their vibrant colors, or their symbolic meanings, the December birthstones remain enduring symbols of beauty and personal expression.