The month of August is unique in the birthstone calendar, offering a diverse trio of gemstones: the vibrant green peridot, the versatile spinel, and the banded sardonyx. Each of these stones carries its own distinct history, geological origin, and symbolic meaning, providing August-born individuals with a wide spectrum of colors and styles to choose from. While peridot has long been recognized as the primary August birthstone, spinel and sardonyx have been incorporated into modern lists, reflecting the evolving nature of birthstone traditions. This article explores the gemological properties, historical significance, and cultural lore of these three remarkable gemstones, drawing upon authoritative sources to provide a comprehensive guide for enthusiasts, collectors, and jewelry buyers.
History and Lore
The tradition of associating specific gemstones with birth months has deep roots, evolving over centuries from ancient beliefs to modern commercial standards. The modern birthstone chart was first standardized in the United States by the National Association of Jewelers (now Jewelers of America) in the early 20th century. Since then, the list has undergone several revisions to include additional stones, offering more choices and reflecting new discoveries and market trends.
For August, the primary modern birthstone is peridot. However, the list has expanded to include spinel and sardonyx. Spinel was added to the August birthstone list relatively recently, providing a durable and colorful alternative. Sardonyx, a banded variety of chalcedony, is listed as a traditional or alternative birthstone for August in some charts. Its use dates back thousands of years, particularly in the creation of cameos, which have been popular in jewelry for at least 2,000 years.
The historical journey of these stones is intertwined with trade, exploration, and cultural exchange. Peridot, for instance, has been known since antiquity, with sources in Egypt and other regions. Spinel, often mistaken for ruby or sapphire throughout history, was only recognized as a distinct mineral in the late 18th century. Sardonyx, with its distinctive bands, was prized by ancient civilizations for engraving and cameos, valued for both its aesthetic appeal and workability.
Geological Formation and Sources
Understanding the geological origins of these gemstones enhances appreciation for their natural beauty and rarity. Each of the August birthstones forms under different conditions and is sourced from distinct regions around the world.
Peridot
Peridot is the gem-quality variety of the mineral olivine, a magnesium iron silicate. It forms deep within the Earth's mantle and is brought to the surface through volcanic activity. Unlike many gemstones, peridot can be found in a single color—a distinctive olive green—though the shade can vary from yellowish-green to brownish-green depending on the iron content. Significant sources of peridot include Egypt, Myanmar, and the United States (notably Arizona and Hawaii). The gemstone is also found in meteorites, though such extraterrestrial peridot is extremely rare and not typically used in jewelry.
Spinel
Spinel is a magnesium aluminum oxide with a complex crystal structure. It occurs in a wide range of colors, including red, blue, pink, purple, and black. The red variety, which closely resembles ruby, has been a source of historical confusion. Spinel forms in metamorphic rocks and is often found in alluvial deposits. Major sources include Myanmar (Burma), Sri Lanka, Thailand, and Vietnam. The gem's durability—ranking 8 on the Mohs hardness scale—makes it suitable for all types of jewelry, and its color variety ensures it can cater to diverse aesthetic preferences.
Sardonyx
Sardonyx is a banded variety of chalcedony, a microcrystalline form of quartz. It consists of alternating layers of sard (a brownish-red chalcedony) and onyx (a black or white chalcedony), creating straight, parallel bands. This gemstone forms in volcanic rock cavities and is often found in regions with significant volcanic activity. Notable sources include India, Brazil, Germany, and the United States (particularly in the Great Lakes region). Sardonyx has been used for centuries in cameos and intaglios, where its layered structure allows for intricate carving and design.
Gemological Properties
The physical and optical characteristics of a gemstone determine its durability, appearance, and value. The table below summarizes key gemological properties for the three August birthstones, based on data from authoritative sources.
| Gemstone | Chemical Formula | Mohs Hardness | Crystal System | Typical Colors | Key Characteristics |
|---|---|---|---|---|---|
| Peridot | (Mg,Fe)₂SiO₄ | 6.5–7.0 | Orthorhombic | Olive green | Single-color variety; forms in mantle; found in volcanic rocks |
| Spinel | MgAl₂O₄ | 8.0 | Cubic | Red, blue, pink, black, etc. | High durability; often mistaken for ruby or sapphire |
| Sardonyx | SiO₂ (quartz) | 6.5–7.0 | Microcrystalline | Banded brown, red, black, white | Layered structure; ideal for carving and cameos |
Peridot
Peridot has a Mohs hardness of 6.5 to 7.0, making it moderately durable but susceptible to scratching if not handled with care. Its refractive index ranges from 1.65 to 1.69, and it exhibits strong dichroism, meaning it can show slightly different shades of green when viewed from different angles. Peridot is typically cut into faceted gems to enhance its brilliance, though cabochon cuts are also common for larger stones. Clarity is generally good, with inclusions often resembling small, parallel needles or tiny gas bubbles.
Spinel
Spinel ranks 8 on the Mohs scale, placing it among the harder gemstones suitable for daily wear. It has a refractive index of approximately 1.72 and a high specific gravity (3.58–3.61). Spinel is known for its exceptional clarity, with few inclusions, and it lacks the pleochroism common in many colored gemstones. This gemstone is cut in a variety of styles, from simple faceted rounds to elaborate designer cuts, to showcase its vibrant colors.
Sardonyx
Sardonyx, as a variety of chalcedony, has a Mohs hardness of 6.5 to 7.0. It is opaque and typically cut en cabochon or carved into cameos to highlight its banded patterns. The gemstone's luster is waxy to vitreous, and its specific gravity ranges from 2.60 to 2.64. Due to its layered structure, sardonyx is not typically faceted; instead, it is valued for its intricate banding, which can be enhanced through polishing and carving.
Symbolism and Metaphysical Beliefs
Gemstones have long been attributed with symbolic meanings and metaphysical properties, often tied to their color, historical use, or cultural lore. While these beliefs are not scientifically verified, they remain an important aspect of the gemstone's cultural legacy.
Peridot
Peridot is often associated with strength, protection, and good fortune. Ancient Egyptians referred to it as the "gem of the sun," believing it could ward off evil spirits and bring happiness. It is also linked to healing and renewal, with some traditions suggesting it can alleviate stress and promote emotional balance. In modern metaphysical beliefs, peridot is said to foster growth, abundance, and positive energy.
Spinel
Spinel's symbolism varies by color, but it is generally regarded as a stone of vitality and renewal. Red spinel, in particular, has been associated with passion and energy, while blue spinel is linked to calmness and clarity. Historically, spinel was thought to protect against harm and bring prosperity. Its durability is often seen as a metaphor for resilience and longevity.
Sardonyx
Sardonyx has been valued since antiquity for its protective and communicative properties. In ancient Rome, it was believed to bring courage and eloquence, making it a popular choice for signet rings and amulets. The stone is also associated with honor and integrity, and its layered bands are said to symbolize unity and balance. In some traditions, sardonyx is used to enhance self-control and discipline.
Care and Cleaning
Proper maintenance is essential to preserve the beauty and longevity of gemstone jewelry. The care requirements for each August birthstone depend on its hardness, cleavage, and other physical properties.
Peridot
Due to its moderate hardness (6.5–7.0) and lack of cleavage, peridot is relatively durable but can be scratched by harder materials. It is safe to clean peridot jewelry using warm, soapy water and a soft brush. Avoid ultrasonic cleaners and steam cleaning, as sudden temperature changes can cause damage. Store peridot separately from other jewelry to prevent scratching.
Spinel
Spinel's high hardness (8.0) and lack of cleavage make it one of the more durable gemstones. It can be cleaned with warm, soapy water and a soft cloth. Ultrasonic cleaners are generally safe for spinel, but it is advisable to avoid extreme temperature changes. Due to its durability, spinel is well-suited for rings and other frequently worn pieces.
Sardonyx
As a variety of chalcedony, sardonyx has moderate hardness (6.5–7.0) and is relatively tough. It can be cleaned with mild soap, water, and a soft brush. Avoid harsh chemicals and ultrasonic cleaners, as they may damage the stone's surface or affect its polish. Sardonyx is often used in carved pieces, which require gentle handling to preserve intricate details.
Conclusion
The August birthstones—peridot, spinel, and sardonyx—offer a remarkable range of colors, histories, and properties. Peridot, with its vibrant green hue, is the traditional modern choice, symbolizing strength and renewal. Spinel provides exceptional durability and a spectrum of colors, making it a versatile and affordable alternative. Sardonyx, with its ancient legacy in carving and cameos, adds a touch of classical elegance. Together, these gemstones reflect the diversity of nature and the enduring appeal of birthstone traditions. Whether chosen for their beauty, symbolism, or personal significance, each stone carries a unique story waiting to be discovered.