August is one of the few months of the year that boasts three official birthstones: peridot, spinel, and sardonyx. This trio offers a remarkable spectrum of color, from the vibrant lime green of peridot to the rich reds and blues of spinel and the banded earth tones of sardonyx. For centuries, these gems have been valued not only for their beauty but also for their durability and symbolic significance. Peridot, with its unique formation in volcanic rock and meteorites, has been mistaken for emerald throughout history. Spinel, often confused with ruby and sapphire due to its similar colors and durability, has recently gained recognition as a gem worthy of its own identity. Sardonyx, an ancient material prized for cameos, provides a connection to classical artistry. Together, these stones represent the diverse and resilient character of the month of August, offering options for every taste and style of jewelry.
The journey to their modern status is a study in gemological history and tradition. While peridot has long been associated with August, spinel and sardonyx were added to official lists in the 20th century, expanding the choices available to those born in this summer month. Understanding the unique properties, origins, and lore of each stone allows for a deeper appreciation of their value. This article will explore the geological formation, historical significance, gemological properties, and care instructions for peridot, spinel, and sardonyx, drawing upon established gemological knowledge to provide a comprehensive guide to the August birthstones.
Historical Significance and Lore
The historical narrative of August's birthstones is a blend of ancient reverence and modern standardization. Peridot, in particular, has a long and storied past. For centuries, fine peridot crystals have been mistaken for emeralds. The most famous historical example is the "Topaz of St. John," a large, brilliant green gem in the shrine of the Three Kings at the Cologne Cathedral in Germany. For centuries, this gem was believed to be a magnificent emerald, but modern analysis has confirmed it is, in fact, a peridot. This case highlights the historical confusion between these two green gems and underscores peridot's long-standing presence in religious and royal collections.
The association of specific gems with the month of August is a more modern development. The concept of birthstones is often traced back to the Breastplate of Aaron, a religious garment described in the Old Testament that was set with twelve different gemstones, each representing one of the twelve tribes of Israel. The modern birthstone list, however, was formalized by the American National Association of Jewelers (now Jewelers of America) in 1912. This list standardized the birthstones for each month, with peridot being designated for August. In 1952, the list was updated to include spinel as an alternative August birthstone, and later, sardonyx was also recognized, particularly in traditional lists. This evolution reflects a growing understanding of gemology and a desire to provide a broader range of choices.
Spinel, while often overlooked in historical texts, has a rich history of its own. Some of the most famous "rubies" in history, such as the Black Prince's Ruby and the Timur Ruby in the British Crown Jewels, are actually large red spinels. These magnificent stones were mined in the famed Badakhshan region of Central Asia, a historical source for fine spinel. For centuries, these gems were valued alongside true rubies for their color and size, and it is only in relatively recent times that spinel has been properly identified and appreciated as a distinct gem species.
Sardonyx has a history that is deeply intertwined with classical art. As a banded variety of chalcedony, its layered structure made it an ideal material for carving cameos and intaglios. The ancient Greeks and Romans were masters of this art form, creating intricate portraits and mythological scenes on sardonyx. These carved gems were highly prized as signets, amulets, and decorative jewelry. The durability and contrasting bands of sardonyx allowed artisans to create dramatic and visually striking pieces, many of which have survived as testaments to the skill of ancient craftsmen.
Geological Formation and Sources
Each of the August birthstones forms under distinct geological conditions, contributing to their unique characteristics and global distribution.
Peridot is the gem variety of the mineral olivine, which is a magnesium iron silicate. Its formation is particularly unique. Peridot is formed deep within the Earth's mantle and is brought to the surface by volcanic activity. Large peridot crystals have also been found in pallasite meteorites, which are stony-iron meteorites that formed in the early solar system. This extraterrestrial origin gives peridot a truly cosmic pedigree. The most significant commercial sources of peridot include Arizona, USA; the island of Zabargad in the Red Sea (historically a major source); Pakistan; and Myanmar. Arizona peridot is often found in basaltic lava flows, while material from Pakistan and Myanmar is typically mined from metamorphic rocks.
Spinel is a magnesium aluminum oxide (MgAl₂O₄) that forms in the metamorphic rock environment, particularly in magnesium-rich limestones and dolomites that have been subjected to high heat and pressure. It can also form in alluvial deposits. Historically, the most important source for red and blue spinel was the Badakhshan region of Afghanistan and Tajikistan, which supplied the world for centuries. Today, the majority of commercial spinel comes from Sri Lanka, which is renowned for its vibrant colors. Other notable sources include Vietnam, Myanmar, and Tanzania, which produces large, clean crystals in a variety of colors.
Sardonyx is a variety of chalcedony, which is a microcrystalline form of quartz (silicon dioxide, SiO₂). It is formed in the cavities of volcanic rocks. As silica-rich water evaporates, layers of silica are deposited, creating the characteristic parallel bands of alternating colors—typically a brownish-red or orange layer (sard) and a white or black layer (onyx). Sardonyx is found in several locations, including Brazil, India, Germany, and the United States. The quality of sardonyx is judged by the sharpness and contrast of its bands, as well as its overall color and translucency.
Gemological Properties
Understanding the physical and optical properties of these gems is essential for identification, valuation, and proper care. The following table summarizes key gemological data for the three August birthstones.
| Property | Peridot | Spinel | Sardonyx (Chalcedony) |
|---|---|---|---|
| Chemical Formula | (Mg,Fe)₂SiO₄ | MgAl₂O₄ | SiO₂ |
| Crystal System | Orthorhombic | Cubic | Trigonal (microcrystalline) |
| Mohs Hardness | 6.5 - 7 | 8 | 6.5 - 7 |
| Refractive Index | 1.635 - 1.690 | 1.718 | 1.53 - 1.54 |
| Specific Gravity | 3.22 - 4.39 | 3.58 - 3.61 | 2.58 - 2.64 |
| Common Colors | Olive to olive-green | Red, blue, pink, purple, black, white | Banded brown, black, white, orange |
| Transparency | Transparent to translucent | Transparent to translucent | Translucent to opaque |
| Key Identifiers | Single refraction, unique olive-green color | Single refraction, high hardness, often flawless | Banded structure, microcrystalline texture |
Peridot is a relatively hard gem, making it suitable for most types of jewelry, though it can be prone to chipping if struck hard. Its most distinctive feature is its color, which ranges from a light yellowish-green to a deep olive-green. The color is caused by the presence of iron. Peridot is a single-refractive gem, meaning it does not exhibit dichroism. It often contains inclusions, such as "lily pads" (small, disk-shaped fluid inclusions) or needle-like crystals, which can help gemologists identify it.
Spinel is one of the hardest and most durable of all gemstones, with a Mohs hardness of 8. This makes it an excellent choice for rings and other jewelry that will be worn daily. Like peridot, spinel is single-refractive. Its most famous colors are a vibrant red (often compared to ruby) and a rich blue (compared to sapphire), but it occurs in a vast array of colors. Red spinel gets its color from trace amounts of chromium, while blue spinel is colored by iron or titanium. Spinel is typically very clean, with few inclusions, which contributes to its brilliance and clarity.
Sardonyx is a variety of chalcedony, which is composed of microscopic quartz crystals. This gives it a waxy luster and a hardness of 6.5 to 7, similar to peridot. Its defining characteristic is its banding, which results from the alternating deposition of different colored layers of silica. Sardonyx is often cut en cabochon (a smooth, rounded shape) to best display its bands. It is not as brilliant or refractive as peridot or spinel due to its microcrystalline nature, but its unique pattern and historical use in carved gemstones give it a distinct appeal.
Symbolism and Metaphysical Beliefs
Throughout history, gemstones have been attributed with symbolic meanings and metaphysical powers. These beliefs add a layer of cultural significance to the physical beauty of the stones.
Peridot has long been associated with protection, healing, and prosperity. In ancient times, it was believed to ward off evil spirits and nightmares. The ancient Egyptians mined peridot on the Red Sea island of Zabargad, and they called it the "gem of the sun." It was thought to have protective powers and was often set in gold. Peridot is also linked to the heart chakra in modern crystal healing practices, where it is believed to promote emotional balance, compassion, and forgiveness. Its vibrant green color is associated with growth, renewal, and vitality.
Spinel, while historically confused with ruby and sapphire, has developed its own set of symbolic meanings. Its durability and wide range of colors have made it a symbol of resilience and versatility. In some traditions, red spinel is associated with passion and vitality, while blue spinel is linked to wisdom and clarity. Because spinel often forms in well-defined crystals, it is sometimes seen as a stone of order and structure. Its recent elevation to a distinct birthstone status has given it a new identity, representing individuality and the breaking of old confusions.
Sardonyx has a rich history of symbolism tied to its use in cameos and amulets. In ancient Rome, sardonyx was a stone of courage and protection. Roman soldiers would often wear sardonyx rings or amulets, believing they would grant them strength in battle and protect them from harm. It was also associated with eloquence and was used as a seal stone for important documents. In later traditions, sardonyx became a stone of marital happiness and stability, with its alternating bands symbolizing the harmony and balance of a successful partnership. Its connection to ancient art and craftsmanship gives it a symbolic link to creativity and legacy.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone jewelry. The physical properties of peridot, spinel, and sardonyx dictate specific care instructions.
Peridot requires careful handling due to its moderate hardness and perfect cleavage in one direction. This means it can be split along a specific plane if struck with sufficient force. It is best to avoid ultrasonic cleaners and steam cleaners for peridot, as sudden temperature changes can cause fractures. The safest method for cleaning peridot is with warm water, a mild dish soap, and a soft brush. After cleaning, rinse thoroughly and dry with a soft, lint-free cloth. When storing peridot jewelry, keep it separate from other gems to prevent scratches, as peridot is softer than many other gemstones.
Spinel is one of the most durable birthstones and is relatively easy to care for. Its high hardness (8 on the Mohs scale) and lack of cleavage make it resistant to scratching and breaking. Spinel can be safely cleaned with warm soapy water and a soft brush. It is also generally safe for ultrasonic cleaning, though it is always best to check with a professional jeweler if the stone is set in a delicate or older mounting. Because spinel is durable, it can be worn daily without much concern, but like all fine jewelry, it should be removed during strenuous activities to avoid impact.
Sardonyx, as a variety of chalcedony, is relatively durable but can be scratched by harder materials. It is safe to clean with warm, soapy water and a soft brush. Avoid harsh chemicals and ultrasonic cleaners, as they may damage the stone or its setting. Sardonyx is often used in cameos and beads, which can be more delicate. For carved sardonyx pieces, gentle cleaning is paramount to preserve the fine details of the carving. Store sardonyx jewelry separately to prevent it from being scratched by harder gems.
Conclusion
The three birthstones of August—peridot, spinel, and sardonyx—offer a compelling trio that embodies both beauty and resilience. Peridot, with its cosmic origins and vibrant green hue, provides a connection to the earth and the heavens. Spinel, with its exceptional durability and dazzling array of colors, challenges historical misconceptions to stand as a gem of distinct character. Sardonyx, with its ancient roots in artistry and symbolism, offers a tangible link to the classical world. Together, they provide a diverse palette of options for those born in August, from the classic elegance of a peridot ring to the brilliant sparkle of a spinel pendant or the historical gravitas of a sardonyx cameo. Understanding the unique story, properties, and care of each stone allows for a deeper appreciation of these remarkable gems, ensuring they can be cherished for generations to come.