The month of August is uniquely represented in the world of gemology by three distinct official birthstones: peridot, spinel, and sardonyx. This trio offers a remarkable diversity in color, origin, and symbolism, providing those born in the eighth month of the year with a wide array of choices for personal adornment and meaning. While peridot stands as the primary modern birthstone, celebrated for its vibrant green glow, spinel and sardonyx serve as historic and traditional alternatives, each with a rich legacy. The collective palette ranges from the brilliant lime-green of peridot to the fiery reds and varied hues of spinel, and the bold, banded patterns of sardonyx. This article delves into the history, geological formation, gemological properties, and cultural significance of each of these three August birthstones, offering a comprehensive guide for gemstone enthusiasts, jewelry buyers, and students of gemology.
History and Lore
The history of the August birthstones spans millennia, with sardonyx being the most ancient of the trio. As a combination of two types of chalcedony, sardonyx has been valued since antiquity for its practical and symbolic uses. In ancient Rome, it was a popular stone for seals and signet rings because hot wax would not adhere to its surface, making it ideal for imprinting official documents. This practical application underscores its long-standing association with stability and authority.
Peridot has a history that is both ancient and often confused with other green gems. The name "peridot" is believed to derive from the Arabic word "faridat," meaning gem. Throughout history, peridot has been frequently mistaken for other green gemstones, including emerald and topaz. Notably, many "emeralds" found in medieval European cathedral treasures have been later identified as peridots. This historical confusion highlights peridot’s enduring appeal and its capacity to rival the beauty of more renowned gems.
Spinel, the most recently added official August birthstone, carries a royal history, often mistaken for ruby. The most sought-after color in spinel is a vivid red that closely rivals the coveted ruby. For centuries, magnificent red spinels were misidentified as rubies, earning them a place in royal collections under the guise of another gem. It was not until more advanced gemological testing was developed that spinel was recognized as a distinct mineral species. Its official inclusion as an August birthstone by the American Gem Trade Association (AGTA) and Jewelers of America (JA) occurred in 2016, adding a modern, versatile option to the traditional list.
The journey of these stones to becoming official birthstones reflects a broader trend in the gem trade. Sardonyx is the traditional August birthstone. Peridot was officially designated as the primary August birthstone in 1912, a standardization effort that sought to provide a single gem for each month. The addition of spinel in 2016 was part of a modern update to these lists, which aims to offer consumers more options in terms of color, affordability, and availability. This evolution demonstrates how birthstone lists are not static but adapt to reflect new discoveries, market trends, and consumer preferences.
Geological Formation and Sources
The three August birthstones originate from vastly different geological processes and are mined in distinct regions across the globe.
Peridot, the gem-quality variety of the mineral olivine, forms deep within the Earth's mantle. It is brought to the surface through volcanic activity. Unlike many gemstones that derive their color from trace impurities, peridot’s distinctive green hue comes from the presence of iron within its own crystal structure. This iron content is also what causes the shade to vary, from yellowish-green to olive to brownish-green. Major sources of peridot include Pakistan, which is known for producing large, high-quality crystals, and the San Carlos Apache Reservation in Arizona, USA, which has been a significant source for centuries. Peridot is also found in Egypt, Myanmar, and Australia.
Spinel is a magnesium aluminum oxide (MgAl₂O₄) that forms in metamorphic rocks and alluvial deposits. It is often found in the same regions as corundum (ruby and sapphire). Key sources for spinel include Myanmar (Burma), which is famed for its "pigeon's blood" red spinels, and Sri Lanka, which produces a wide range of colors. The Luc Yen region in northern Vietnam has been producing high-quality spinel since the 1980s, with mines yielding deep red, purple, pink, violet, and violet-blue stones. A significant 2007 discovery in Tanzania produced pinkish and orangy red spinel, with mines there also yielding purple and blue hues. The gems from Luc Yen are so naturally lustrous that locals refer to them as "spirit polished."
Sardonyx is a banded variety of chalcedony, which is a cryptocrystalline form of quartz (silicon dioxide, SiO₂). It consists of alternating layers of sard (a brownish-red to orange variety of chalcedony) and onyx (typically white or black chalcedony). This banding is a result of the sequential deposition of silica-rich fluids in rock cavities over time. While specific mining locations are not detailed in the provided materials, chalcedony deposits are widespread globally. Sardonyx's formation process is similar to that of other agates and onyxes, requiring specific geological conditions to create its characteristic layered appearance.
Gemological Properties
Understanding the physical and chemical properties of these gemstones is crucial for their identification, care, and use in jewelry. The following table summarizes key gemological data for peridot, spinel, and sardonyx.
| Property | Peridot | Spinel | Sardonyx |
|---|---|---|---|
| Mineral Species | Olivine (Forsterite-Fayalite series) | Spinel | Chalcedony (Quartz) |
| Chemical Formula | (Mg, Fe)₂SiO₄ | MgAl₂O₄ | SiO₂ |
| Crystal System | Orthorhombic | Cubic | Trigonal (microcrystalline) |
| Hardness (Mohs Scale) | 6.5 - 7 | 8 | 7 |
| Refractive Index | 1.65 - 1.69 | 1.71 - 1.73 | 1.53 - 1.54 |
| Specific Gravity | 3.34 - 3.48 | 3.58 - 3.61 | 2.58 - 2.64 |
| Color | Green (yellowish-green to olive) | Red, pink, orange, purple, blue, black | Banded red, brown, white, orange |
| Clarity | Often includes "lily pad" inclusions | Can be clean to heavily included | Opaque to translucent, banded |
Peridot is a relatively hard gemstone with a Mohs hardness of 6.5 to 7, making it suitable for most jewelry types, though care should be taken to avoid hard impacts. Its refractive index is moderate, and it often contains characteristic "lily pad" inclusions, which are tiny, plate-like crystals. The most prized peridot is a vivid olive-green.
Spinel is notably durable, ranking 8 on the Mohs scale, which makes it an excellent choice for rings and other jewelry that experiences daily wear. It is stable when exposed to light and most chemicals, though some colors may fade under high heat. Ultrasonic and steam cleaners are generally safe, but any fractures should be considered; warm, soapy water is a universally safe cleaning method.
Sardonyx, as a variety of chalcedony, has a hardness of 7 on the Mohs scale. It is composed of microscopic quartz crystals, giving it an opaque to translucent appearance. Its defining characteristic is the banding of sard and onyx layers, which creates unique patterns in each stone. Its refractive index and specific gravity are lower than those of peridot and spinel, consistent with its quartz composition.
Symbolism and Metaphysical Beliefs
Beyond their physical beauty, the August birthstones are rich in symbolism and metaphysical lore, each offering a different set of meanings and energies.
Peridot is strongly associated with positive emotions and abundance. It is believed to symbolize joy, healing, and emotional clarity. Many consider it a stone that can boost mood, confidence, and open the heart to love. Its vibrant green color is often linked to the Heart Chakra in crystal healing practices, supporting emotional healing and the release of negative patterns.
Spinel is a stone of renewal, inspiration, and vitality. Its wide range of colors allows it to be matched to specific intentions. Red spinel is often associated with energy and passion, while blue spinel may be linked to calm and communication. It is considered a high-energy stone that can inspire hope, encourage resilience through hard times, and restore depleted energy reserves. Its royal history also lends it an aura of nobility and modern style.
Sardonyx, the most ancient of the trio, is a grounding and protective stone. It stands for strength, stability, and protection. Historically used for seals, it symbolizes authority and steadfastness. In metaphysical beliefs, sardonyx is thought to promote courage, stable relationships, and a sense of security. Its earthy, banded appearance makes it a favorite for those seeking a gem with deep roots and a connection to ancient traditions.
Care and Cleaning
Proper care is essential to maintain the beauty and longevity of any gemstone. The different physical properties of peridot, spinel, and sardonyx dictate specific care guidelines.
Peridot requires careful handling due to its relative softness (6.5-7 on the Mohs scale) and a tendency to be brittle. It should be protected from hard blows and extreme temperature changes, which can cause fracturing. Cleaning is best done with warm, soapy water and a soft brush. Ultrasonic cleaners are generally not recommended, and steam cleaning should be avoided.
Spinel is one of the more durable birthstones. With a hardness of 8, it is resistant to scratching and can withstand the rigors of daily wear. It is stable to light and chemicals, making it relatively low-maintenance. Ultrasonic and steam cleaners are typically safe for spinel without fractures. As with all gemstones, warm, soapy water with a soft brush is a safe and effective cleaning method.
Sardonyx, with a hardness of 7, is also durable for jewelry. As a cryptocrystalline quartz, it is stable and can be cleaned with warm, soapy water and a soft brush. It is generally safe for ultrasonic cleaning, but caution is advised if the stone has any fractures or if it is set in a delicate piece of jewelry. Avoid harsh chemicals and sudden temperature changes.
Conclusion
The August birthstones—peridot, spinel, and sardonyx—offer a remarkable trifecta of beauty, history, and meaning. From the ancient, banded strength of sardonyx to the historically mistaken brilliance of spinel and the universally joyful green of peridot, each stone provides a unique connection to the natural world and human culture. Their diverse origins, from volcanic depths to metamorphic formations, and their distinct gemological properties, from the hardness of spinel to the characteristic inclusions of peridot, make them a fascinating subject of study and appreciation. For those born in August, this trio provides not just a color choice, but a selection of gems with deep symbolic resonance, ensuring that every piece of jewelry can carry a personal and timeless significance.