The month of December is uniquely associated with two distinct gemstones: the historically significant Zircon and the modern addition of Tanzanite. These stones, while different in composition and appearance, both capture the essence of winter with their captivating colors and unique optical properties. Zircon, a gemstone with a history stretching back centuries, offers a vibrant fire and a spectrum of colors, most notably the treated blue that dominates the market. Tanzanite, a relative newcomer to the gem world, is prized for its mesmerizing pleochroism and rich violet-blue hues. This article delves into the geological origins, gemological characteristics, historical significance, and cultural lore of these two December birthstones, providing a comprehensive guide for enthusiasts, collectors, and those born in the final month of the year.
Zircon: The Gem of Many Colors and Historic Fire
Zircon is a gemstone that serves as a birthstone for the month of December. It is a bright gem with high luster, and many specimens produce a colorful fire that is similar to diamond. Because of these properties, zircon was once used as an alternative stone for diamond. Zircon gives the shopper an opportunity to select from a variety of colors. Blue is the most popular zircon color. Most natural zircons are yellow, red or brown, but heat and irradiation treatments can transform them into blue, green and many other colors. About 80% of the zircons sold today are blue, with the color produced by treatment. Zircon replaced lapis lazuli as a modern birthstone in 1952.
The historical journey of zircon is marked by its mistaken identity and its eventual recognition as a distinct and valuable gem. For centuries, many people confused zircon with diamond due to its high refractive index and brilliant luster. This confusion led to zircon being called "jacinth" or "hyacinth" in historical texts. However, despite its diamond-like sparkle, zircon is a different mineral altogether. Its use as a diamond simulant in the past highlights its visual appeal and durability, though it is much softer than diamond and more prone to damage.
The color variety of zircon is one of its most appealing attributes. While natural zircon is most commonly found in yellow, red, or brown shades, the gem can be treated to produce a wide array of colors. The most sought-after color in the market today is blue. This blue color is typically achieved through a controlled heating process, which transforms the original brown or yellow crystals into a stable and attractive blue. Other colors such as green, yellow, and even reddish hues can also be produced through treatment. The ability to enhance zircon's color has made it a versatile and affordable choice for jewelry, allowing consumers to select from a color suite that includes rose, peach, yellow, green, blue, honey, white, champagne, cognac, and mocha shades.
Tanzanite: The New Gem with a Unique Color Play
Tanzanite is the newest birthstone for the month of December. Most tanzanite sold in jewelry today has a blue to bluish purple to bluish violet color that is produced by heat treatment. Its color has an interesting feature - it changes depending upon the angle of viewing. This phenomenon is known as pleochroism, and it is a defining characteristic of tanzanite. When viewed from different directions, a single tanzanite crystal can display three distinct colors: blue, violet, and burgundy. This dramatic color shift makes tanzanite a captivating and dynamic gemstone, ensuring that no two stones look exactly alike from every angle.
Tanzanite's story is a modern gemological tale. It was discovered in the late 1960s in the Merelani Hills of Tanzania, East Africa, and was quickly recognized for its unique beauty. The gemstone was initially named "blue zoisite" but was later rebranded as "tanzanite" by Tiffany & Co., who recognized its potential and became its primary promoter. Its rarity is a key part of its allure; it is found in only one location in the world, making it significantly rarer than diamond. This geographic limitation adds to its value and desirability.
The heat treatment process is crucial for most tanzanite on the market. In its natural state, tanzanite is often a brownish color. A careful heating process, which mimics the natural geological conditions that would eventually transform the stone, removes the brownish tint and reveals the gem's signature blue-violet color. This treatment is widely accepted in the industry and is considered permanent. The resulting gem is stable and suitable for all types of jewelry, though its moderate hardness requires careful handling.
Geological Formation and Sources
Understanding the geological origins of these gems adds depth to their appreciation. Zircon is a mineral belonging to the nesosilicate group, with a chemical formula of ZrSiO₄. It is one of the oldest minerals on Earth, often found in igneous and metamorphic rocks. It forms in high-temperature environments and can be found in granites and pegmatites. Significant sources of gem-quality zircon include Australia, Cambodia, Myanmar, and Sri Lanka. Australian zircon, particularly from the state of Queensland, is known for its high-quality brown and golden-yellow crystals. Cambodian zircon is often celebrated for its fine blue color after treatment. These locations provide the raw crystals that are cut and treated to become the beautiful gems found in jewelry stores.
Tanzanite, on the other hand, has a very specific and limited origin. It is a variety of the mineral zoisite, which is a calcium aluminum silicate hydroxide. The only known source of gem-quality tanzanite is the Merelani Hills in the Manyara Region of Tanzania. This area is not large—estimated to be only a few square kilometers—and the gemstone is found in a single vertical vein. The formation of tanzanite is linked to a unique geological event. Around 500 million years ago, tectonic plate movements and volcanic activity in the East African Rift created the conditions for the formation of zoisite crystals. The process was interrupted, and the crystals were not subjected to the intense heat and pressure that would have completely metamorphosed them. Instead, they were exposed to later heat from volcanic activity, which altered their chemistry and color. This specific and rare sequence of events makes tanzanite's occurrence a geological anomaly. The mining of tanzanite is a significant economic activity in Tanzania, and efforts are being made to ensure responsible mining practices to preserve this finite resource.
Gemological Properties: A Scientific Comparison
A detailed look at the gemological properties of zircon and tanzanite reveals their differences and helps in understanding their care and value. The following table summarizes key properties based on the information provided in the sources.
| Property | Zircon | Tanzanite |
|---|---|---|
| Mineral Group | Nesosilicate | Zoisite (Amphibole group) |
| Chemical Formula | ZrSiO₄ | Ca₂Al₃(SiO₄)₃(OH) |
| Crystal System | Tetragonal | Orthorhombic |
| Mohs Hardness | 6.5 - 7.5 | 6.5 - 7 |
| Luster | Adamantine (high brilliance) | Vitreous (glassy) |
| Refractive Index | High (1.92-2.01) | 1.691 - 1.700 |
| Pleochroism | Weak to strong (varies by color) | Strong (blue, violet, burgundy) |
| Typical Treatments | Heat, Irradiation (for color) | Heat (to remove brown tint) |
| Common Colors | Blue (treated), yellow, red, brown | Blue-violet, violet-blue |
| Durability | Fair to good; can be brittle | Fair; moderate hardness, good cleavage |
Zircon's most notable property is its high refractive index, which gives it a brilliance and fire that rivals diamond. This "fire" is the dispersion of light into spectral colors, a characteristic that made it a popular diamond simulant. However, zircon has perfect cleavage in two directions, making it susceptible to chipping or breaking if struck hard. Its hardness, ranging from 6.5 to 7.5 on the Mohs scale, makes it suitable for jewelry but not as durable as sapphire or diamond. It is important to protect zircon from sharp blows and extreme temperature changes, which can cause cracking.
Tanzanite's defining gemological feature is its strong pleochroism. This is a direct result of its crystal structure and the presence of vanadium, which is responsible for its color. The pleochroic colors are typically blue along the c-axis, violet along the b-axis, and burgundy along the a-axis. Gem cutters must orient the stone carefully to display the most desirable blue-violet hue in the final gem. With a Mohs hardness of 6.5 to 7, tanzanite is moderately hard but has good cleavage, meaning it can split along certain planes if struck. This makes it a gem that requires careful setting and wearing, ideally not in rings that are exposed to daily knocks, but rather in pendants, earrings, or occasional-wear rings.
History, Lore, and Symbolism
The cultural significance of these gemstones spans centuries and continents. Zircon has a rich history. In the Middle Ages, it was believed to ward off evil and protect travelers. It was also thought to promote honor and purity in its wearer. The blue variety of zircon, in particular, was associated with wisdom and prosperity. Its historical use as a diamond substitute also gave it a place in royal and aristocratic jewelry, where it provided the sparkle of a diamond at a more accessible price point. As a modern birthstone, it carries the legacy of being a gem of clarity and spiritual grounding.
Tanzanite, being a modern discovery, does not have an ancient lore. However, its symbolism has been carefully crafted since its introduction. It is often called the "stone of transformation" due to its dramatic color change and its recent geological birth. It is said to promote spiritual growth, calm the mind, and encourage a higher consciousness. Some also associate it with the throat chakra, believing it enhances communication and self-expression. As a gift, tanzanite is particularly meaningful for those born in December, representing a unique and rare beauty, much like the individual it is given to.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of both zircon and tanzanite. Due to their moderate hardness and cleavage, both stones require gentle handling.
For Zircon: * Cleaning: Use warm, soapy water and a soft brush. Avoid ultrasonic cleaners, as the vibrations can cause fractures in stones with inclusions or cleavage planes. Steam cleaning is also not recommended due to the risk of thermal shock. * Storage: Store zircon jewelry separately in a soft cloth or a lined jewelry box to prevent scratching by harder gems like diamond or sapphire. * Wearing: Avoid wearing zircon jewelry during activities that could expose it to hard knocks, such as sports or heavy manual work. Remove before applying lotions or chemicals.
For Tanzanite: * Cleaning: Similar to zircon, use only mild soap, warm water, and a soft brush. Ultrasonic cleaners and steam cleaners are not safe for tanzanite and can cause damage. * Storage: Store tanzanite separately to avoid scratches. Its cleavage makes it vulnerable, so it should not be stored where it can be jostled or pressed. * Wearing: Due to its cleavage and moderate hardness, tanzanite is best suited for jewelry that is not subjected to daily wear and tear, such as pendants and earrings. If set in a ring, it should have a protective setting and be worn with care.
Conclusion
Zircon and tanzanite, the two birthstones for December, offer a fascinating study in contrasts. Zircon is an ancient gem with a storied past, prized for its brilliant fire and versatile colors, most famously the treated blue that has become its modern hallmark. Tanzanite is a gem of the modern era, born from a unique geological event in a single location on Earth, captivating the world with its dramatic pleochroism and rich violet-blue hues. Both stones, while differing in their origins and properties, share a common appeal: they provide a beautiful and meaningful connection to the month of December. Whether one is drawn to the historical elegance of zircon or the contemporary rarity of tanzanite, each gem offers a unique narrative of color, science, and symbolism, making them enduring treasures for those born in the winter month and for all who appreciate the wonders of the mineral kingdom.