The world of birthstones offers a fascinating intersection of geology, history, and human belief. For the months of May and December, the assigned gemstones—emerald, tanzanite, and turquoise—represent a spectrum of color, origin, and symbolism that has captivated civilizations for millennia. Emerald, the quintessential green gem of May, is a classic birthstone with ancient roots, while December's trio—tanzanite, turquoise, and zircon—presents a modern selection of blue-hued stones, each with a distinct geological story and cultural footprint. This article explores the formation, properties, historical significance, and enduring appeal of these remarkable gemstones, drawing exclusively from authoritative gemological sources to provide a comprehensive overview for enthusiasts, collectors, and students of mineralogy.
History and Lore
The historical narratives of these gemstones are as varied as their colors. The emerald's story is particularly ancient, tracing back to the dawn of civilization. Historical accounts place its earliest known mining in Egypt, as far back as 1500 BCE. The gem was deeply revered in ancient Egyptian culture, symbolizing fertility and rebirth. Its association with royalty is epitomized by Cleopatra, the famed Egyptian queen, who was known for her passion for emeralds and adorned herself with them extensively. Egyptian emerald mines were a significant source of the gem in antiquity, and the stone was also traded and valued in other ancient civilizations.
The journey of emerald from antiquity to the modern birthstone list is a story of evolving tradition. The modern concept of birthstones is largely derived from the Breastplate of Aaron, a religious artifact described in the Book of Exodus, which featured twelve gemstones representing the twelve tribes of Israel. While the exact stones on the breastplate are a matter of scholarly debate, emerald is often cited as one of them. Over centuries, this religious and historical significance helped cement emerald's place in various cultural and astrological traditions. Its selection as a birthstone for May is a relatively modern codification, but one that rests on a deep foundation of historical reverence. For centuries, emeralds have been associated with love, loyalty, and wisdom, and were believed by some to possess healing properties, particularly for the eyes.
In contrast, the history of December's birthstones is more recent, particularly for tanzanite. Turquoise, however, boasts an ancient lineage comparable to emerald. It is one of the oldest gemstones in human history, with evidence of its use in jewelry and ceremonial objects dating back to ancient Egypt and Persia. The name "turquoise" itself derives from the French pierre turquoise, meaning "Turkish stone," as it was brought to Europe from the Ottoman Empire. For millennia, it has been a talisman of protection, wisdom, and good fortune in cultures across the globe, from the Native American peoples of the American Southwest to the nomadic tribes of Central Asia.
Tanzanite's history is a testament to modern gem discovery. It is a relative newcomer to the gemological world, first identified in 1967 in the Merelani Hills of Tanzania. Its discovery was rapid and its rise to prominence swift, earning it a place on the modern birthstone list for December. This placement reflects the dynamic nature of birthstone traditions, which can evolve to include newly discovered and popular gemstones. Zircon, the third December birthstone, has a history that bridges ancient and modern. Blue zircon, in particular, has been valued for centuries, though its use as a prominent birthstone is a more contemporary development.
Geological Formation and Sources
The genesis of these gemstones lies in vastly different geological processes, resulting in their unique characteristics and limited sources of origin.
Emerald: Emerald is a variety of the mineral beryl, with its distinctive green color primarily caused by trace amounts of chromium and vanadium. Its formation requires a rare and specific geological environment. Emeralds typically form in pegmatites and hydrothermal veins, where beryllium-rich fluids interact with chromium- and vanadium-bearing rocks under high pressure and temperature. The primary sources of emeralds historically have been Egypt and Colombia. The Colombian deposits, particularly the Muzo and Chivor mines, are world-renowned for producing emeralds with the most prized deep green hue. Other notable sources include Zambia, Brazil, and Zimbabwe, each yielding stones with slightly different color characteristics.
Turquoise: Turquoise is an opaque, blue-to-green mineral composed of hydrated copper and aluminum phosphate. It forms in arid or semi-arid regions where acidic, copper-rich water percolates through aluminum-bearing rocks. This process, known as secondary mineralization, occurs in the near-surface environment. Turquoise is almost exclusively found in specific regions of the world, with the most significant deposits in the United States (particularly Arizona, Nevada, and New Mexico), Iran (historically the source of the finest "Persian turquoise"), and China. The color of turquoise is directly influenced by its copper content (blue) and iron content (green), with the matrix (the host rock) also contributing to its appearance.
Tanzanite: Tanzanite is the blue-to-violet variety of the mineral zoisite. Its formation is tied to a unique geological event. Approximately 585 million years ago, a massive geological event in the East African Rift system altered the host rock, introducing the necessary elements (calcium, aluminum, silicon, and traces of vanadium) for zoisite to form. The heat from this event caused the vanadium-bearing zoisite to develop its signature blue-to-violet color. Tanzanite is found in only one location on Earth: the Merelani Hills of northern Tanzania, near the base of Mount Kilimanjaro. This extreme geographic restriction makes it exceptionally rare; some geologists estimate that the current deposits could be exhausted within a few decades.
Zircon: Zircon is a mineral composed of zirconium silicate. It is one of the oldest minerals on Earth, with crystals found in ancient rocks dating back billions of years. Blue zircon, the variety most often associated with December, is typically heat-treated to achieve its vibrant blue color from a naturally brown or yellowish-brown hue. Major sources for zircon include Cambodia, Sri Lanka, Thailand, and Australia. The gem's durability and high refractive index make it a popular choice for jewelry.
Gemological Properties
Understanding the physical and chemical properties of these gemstones is crucial for their identification, valuation, and care. The following table summarizes key gemological data for the three primary birthstones discussed.
| Gemstone | Mineral Species | Chemical Formula | Mohs Hardness | Refractive Index | Crystal System | Common Treatments |
|---|---|---|---|---|---|---|
| Emerald | Beryl | Be₃Al₂(SiO₃)₆ | 7.5 - 8 | 1.577 - 1.583 | Hexagonal | Oiling, resin filling (common for clarity enhancement) |
| Turquoise | Phosphate Mineral | CuAl₆(PO₄)₄(OH)₈·4H₂O | 5 - 6 | N/A (opaque) | Triclinic | Stabilization, dyeing, waxing (very common) |
| Tanzanite | Zoisite | Ca₂Al₃(SiO₄)₃(OH) | 6.5 - 7 | 1.691 - 1.700 | Orthorhombic | Heat treatment (to achieve blue color) |
| Zircon | Zircon | ZrSiO₄ | 6.5 - 7.5 | 1.925 - 2.015 | Tetragonal | Heat treatment (for color, especially to blue) |
Emerald: With a Mohs hardness of 7.5 to 8, emerald is relatively durable but is known for its frequent inclusions, which are often called "jardin" (French for garden). These inclusions are a natural part of the stone's character and are used by gemologists to identify natural emeralds. Due to their typical inclusions, emeralds are often treated with oil or resin to fill surface-reaching fractures, improving their clarity and stability. This is a widely accepted industry practice, provided it is disclosed.
Turquoise: As a much softer stone (5-6 on the Mohs scale) and being opaque, turquoise is more susceptible to scratching and damage. Its porosity means it is almost always treated in some way to enhance its durability and color. Stabilization, where the stone is impregnated with a clear resin or wax, is the most common treatment. Dyeing is also used to achieve a more uniform blue color. Natural, untreated turquoise of high quality is rare and valuable.
Tanzanite: With a hardness of 6.5 to 7, tanzanite is suitable for most jewelry but requires reasonable care to avoid scratches. Its most notable property is its strong trichroism, meaning it displays three different colors—blue, violet, and reddish-brown—from different crystal directions. Most tanzanite is heat-treated to remove the brownish component and enhance the blue and violet hues, a stable and permanent treatment. The gem's color is also pleochroic, showing different shades of blue and violet depending on the orientation.
Zircon: Zircon is one of the hardest and most brilliant gemstones, with a Mohs hardness of 6.5 to 7.5 and a very high refractive index, giving it exceptional sparkle that can rival diamond. It is, however, more brittle than diamond. The blue color in most commercial zircon is achieved through heat treatment of natural brown zircon crystals. Untreated natural blue zircon is exceptionally rare.
Symbolism and Metaphysical Beliefs
Beyond their physical properties, these gemstones carry a rich tapestry of symbolic meanings and metaphysical beliefs, many of which have persisted from ancient times to the present day.
Emerald: Historically and culturally, emerald has been a symbol of rebirth, love, and fertility. Its vibrant green is associated with spring, renewal, and the lushness of nature. In many traditions, it is believed to promote emotional balance, spiritual growth, and wisdom. Some ancient cultures even attributed protective qualities to emerald, believing it could ward off evil spirits and enhance foresight. Its association with royalty and luxury has also made it a symbol of power and prestige.
Turquoise: Perhaps no other gemstone is as steeped in protective lore as turquoise. It has long been considered a talisman of protection, safeguarding the wearer from harm and bringing good fortune. For Native American cultures, it is a sacred stone, symbolizing the sky and water, and is used in ceremonies and jewelry. It is also believed to promote healing, peace, and wisdom, and to connect the wearer to the spiritual world.
Tanzanite: As a modern gem, tanzanite's metaphysical properties are a blend of contemporary belief and its zoisite heritage. It is often associated with transformation, intuition, and spiritual awakening. Its striking color is believed to stimulate the throat and third-eye chakras, enhancing communication and psychic abilities. Some also associate it with compassion and a sense of calm, making it a popular stone for meditation.
Zircon: Zircon has been associated with purity, clarity, and wisdom. Historically, it was believed to promote honor and purity in the wearer. Blue zircon, in particular, is linked to peace, rest, and tranquility. It is also considered a stone of prosperity and success, believed to attract wealth and good fortune. Its brilliant sparkle is said to inspire joy and a sense of wonder.
Care and Cleaning
Proper care is essential to maintain the beauty and integrity of these gemstones, with each requiring specific handling due to its unique properties.
Emerald: Due to its common inclusions and treatments, emeralds require gentle care. Avoid ultrasonic cleaners and steam cleaners, as the heat and vibrations can cause existing fractures to expand. The best method for cleaning an emerald is with warm, soapy water and a soft brush. It is also advisable to have emerald jewelry professionally inspected and re-oiled periodically by a reputable jeweler. Store emeralds separately to prevent scratching by harder stones.
Turquoise: As a soft and porous stone, turquoise is particularly vulnerable. It should never be exposed to harsh chemicals, perfumes, lotions, or prolonged sunlight, which can cause fading or damage. Cleaning should be done with a soft, damp cloth only; avoid soaking or using any cleaners. Due to its sensitivity, turquoise is often best set in protective settings like bezels and should be removed during activities that could cause impact or exposure to chemicals.
Tanzanite: With a moderate hardness, tanzanite can be cleaned with warm, soapy water and a soft brush. However, it should be kept away from sudden temperature changes and harsh chemicals. Given its relative softness compared to sapphire or diamond, it is best to store tanzanite jewelry separately to avoid scratches. It is also advisable to remove it during physical activities.
Zircon: While zircon is hard and brilliant, it is brittle and can be chipped by a sharp blow. Cleaning is straightforward: use warm, soapy water and a soft brush. Avoid ultrasonic cleaners, as the vibrations may cause fractures in some stones. Store zircon jewelry carefully, ideally in a fabric-lined box away from other gems to prevent scratching or impact.
Conclusion
The birthstones of May and December—emerald, tanzanite, and turquoise—offer a compelling study in diversity. Emerald, with its ancient history and classic green hue, stands as a testament to geological rarity and enduring cultural value. Turquoise, one of the oldest known gems, carries the weight of millennia of protective lore and artistic expression. Tanzanite represents the thrill of modern discovery, a gem whose entire known source is confined to a few square miles of Tanzania. Together, they illustrate the vast range of the mineral kingdom, from the durable and brilliant zircon to the soft and porous turquoise. Their selection as birthstones provides individuals with a meaningful connection to both the natural world and a rich tapestry of human history, making each stone not just a piece of jewelry, but a story of the earth itself.