The month of August is marked by a unique legacy of three birthstones—peridot, spinel, and sardonyx—each possessing distinct origins, qualities, and cultural significance. Unlike other birth months represented by a single gem, August holds the distinction of being one of only three months (alongside June and December) to be associated with multiple stones. This article delves into the science, history, and symbolism of these August birthstones, offering a comprehensive exploration for enthusiasts, jewelry buyers, and gemology students alike.
From their historical importance in ancient civilizations to their modern popularity in fine jewelry, August’s gemstones reflect both the vitality of summer and the enduring connection between natural beauty and human tradition. Each stone’s characteristics and meanings have evolved through centuries, capturing the imagination and symbolism of those who wear them. Below is an in-depth analysis of each August birthstone, drawing exclusively from authoritative and historical sources.
Historical Significance and Lore
The tradition of assigning gemstones to one’s birth month dates back thousands of years, with early references found in biblical, Roman, and medieval manuscripts. However, the formalized list of modern birthstones is much more recent, with major changes occurring in the 20th century.
August, for instance, has historically been linked to sardonyx—a banded chalcedony in brown, red, and white tones—due to its long-standing use in ancient cultures, particularly in Rome and Greece. By the early 21st century, both peridot and spinel were added to the list as alternatives to sardonyx, reflecting not only their aesthetic appeal but also a broader appreciation for diverse gemstone selections.
Ancient Egyptian records mention the use of peridot as early as 1500 BCE, where it was called the "gem of the sun" and believed to be a gift from the sun god, Ra. The Romans later adopted peridot for use in adornments, often embedding it in jewelry and ornaments for its brilliance and golden green hue.
Similarly, spinel has a long but undervalued history. Its deep red, cobalt blue, and pink hues have often been mistaken for ruby, emerald, and sapphire, leading to centuries of misclassification. Notably, many believed a famous 18th-century ruby to actually be a remarkable red spinel, weighing over 300 carats.
These historical narratives not only enrich our understanding of August birthstones but also underscore their timeless appeal and the evolving perceptions they hold in both cultural and commercial markets.
Geological Formation and Sources
The uniqueness of August’s birthstones lies in their geological origins and the varied environments in which they are formed. Each gemstone has distinct mineralogical and formation processes that contribute to its allure.
Peridot: A Deep-Earth Beauty
Peridot is the gem variety of olivine, a mineral that forms deep within the Earth's mantle at high temperatures and pressures. This process explains why peridot is often found in igneous rocks, specifically those formed from cooled lava. Interestingly, peridot can also be discovered within lunar and meteoritic materials, a phenomenon captured in a famous find on the Asteroid 4-Vesta, where the mineral was observed in extraterrestrial rock samples.
The primary sources of peridot today are Zambia, Vietnam, Madagascar, and The United States (Arizona). Zambian peridot, especially, is renowned for its vibrant and rich olive-green color, making it highly desirable in the gemstone trade.
Peridot's formation in molten rock results in a relatively uniform crystal structure, with inclusions (internal features) that can include two-phase liquids trapped inside the crystal. These inclusions, known as "fingerprint inclusions," often form characteristic swirling patterns under magnification. They are not detrimental to the gemstone’s beauty but instead serve as distinguishing features that help gemologists identify peridot.
Spinel: The Misunderstood Marvel
Spinel is a magnesium aluminum oxide with a diverse chemical composition that allows for a dazzling array of colors, including red, blue, pink, and black. Its formation is primarily associated with metamorphic and igneous rock environments, where heat and pressure transform minerals over millions of years.
The finest red and pink spinel is commonly found in Afghanistan, Sri Lanka, and Myanmar (Burma). Notably, the Star of India, a famous star sapphire in the American Museum of Natural History, was later correctly identified as a red or "ruby" spinel, highlighting the gem’s historical misattribution.
Spinel is also mined in Brazil, Nepal, and Vietnam, where its vibrant colors make it a popular alternative to more common gemstones like ruby and sapphire. Its isostructural crystal system—where the same atomic arrangement allows for a wide variety of colors—makes it a versatile and attractive gemstone in modern jewelry design.
Sardonyx: The Stone of Layers
Sardonyx is a type of chalcedony, itself a microcrystalline variety of silicon dioxide (SiO₂). It is defined by its banded appearance, alternating layers of sard (a reddish-brown chalcedony) and onyx (a black or white chalcedony). This banding is both visually striking and historically significant, as it was highly favored in sealing rings used in ancient Rome and during the Renaissance.
Sardonyx deposits are found in several countries, including India, Germany, Brazil, and the United States. Some of the most ancient and prized sardonyx stones were sourced from the Near East and Mediterranean regions, particularly from quarries in Phrygia (modern Turkey). Roman scholars such as Pliny the Elder wrote extensively about sardonyx, often describing its use in engraved intaglios and signet rings.
Although synthetically produced sardonyx is common in modern times, the most authentic and valuable specimens are those that exhibit naturally occurring banded patterns, with each layer representing a different geological episode.
Gemological Properties
To choose and care for a gemstone effectively, it’s essential to understand its physical and optical properties. Peridot, spinel, and sardonyx each possess unique characteristics that influence their usage in jewelry and their susceptibility to damage.
Peridot: The Green Dynamo
Peridot is a silicate mineral with the chemical formula (Mg,Fe)₂SiO₄. Its color varies from olive-green to rich yellow-green, depending on the amount of iron in the crystal structure. The gem’s transparency typically ranges from translucent to transparent, with a refractive index (RI) of 1.65 to 1.69, giving it a bright, glassy luster.
On the Mohs scale of hardness, peridot rates between 6.5 and 7, which makes it relatively durable but still susceptible to scratches from harder materials like quartz or topaz. As such, it is not the best choice for high-impact jewelry such as rings, but performs well in pendants and earrings.
Peridot also has a conchoidal fracture and no cleavage, meaning it shatters in a curved pattern when struck. While this can be a risk in jewelry, peridot is still widely used due to its striking appearance and affordability compared to other colored gems.
Spinel: A Hard and Resilient Beauty
Spinel’s chemical formula is MgAl₂O₄, and it exists in a wide range of colors, including red, pink, orange, blue, and black. The gem is prized for its high luster and clarity, with a refractive index of 1.718, often outshining even sapphire in brilliance when properly cut.
On the Mohs scale, spinel has a hardness of 8, which is significantly harder than peridot and closer in durability to sapphire or zircon. This makes spinel an excellent choice for rings and daily wear. It is also tough and has no cleavage, ensuring that it is less prone to chipping or breaking than many other gemstones.
Color variations in spinel are determined by trace elements such as chromium, manganese, or iron. For example, red spinel is often due to chromium impurities, while pink spinel results from manganese. The gem’s isotropic crystal structure (lacking double refraction) gives it a consistent and dazzling light return.
Sardonyx: The Banded Marvel
Sardonyx, being a form of chalcedony, is primarily composed of silicon dioxide (SiO₂). Its transparency ranges from opaque to translucent, and the banding is a result of alternating mineral layers deposited during formation.
The Mohs hardness of sardonyx is 6.5 to 7, similar to peridot, and it has a conchoidal fracture. However, because of its banded and often opaque nature, it is more frequently used in cameo carvings, engraved seals, and intaglios rather than faceted gems.
The refractive index ranges from 1.48 to 1.53, and the gem is dichroic (displaying two colors), a feature that can enhance its appeal in cabochon or carved stones. One of sardonyx’s most notable traits is that its colors are very stable under light, which is ideal for long-term display and wear.
Care and Maintenance
Caring for August birthstones is essential to preserving their beauty and value over time. Given their unique properties, different considerations apply to each gemstone.
Peridot
Due to its 6.5–7 hardness, peridot can be scratched by harder gemstones or materials if not stored properly. Always store peridot separately from harder gemstones like topaz or quartz.
When it comes to cleaning, a soft microfiber cloth and mild soapy water are ideal. Ultrasonic or steam cleaners are not recommended because peridot may contain two-phase inclusions that can expand and potentially damage the stone if subjected to excessive vibrations or heat.
Spinel
Spinel's hardness of 8 and lack of cleavage make it highly durable and suitable for everyday wear. You can place spinel in an ultrasonic or steam cleaner for a quick and efficient clean. However, always avoid exposure to harsh chemicals during cleaning, and clean the gem after wearing it in situations involving oils or lotions.
Sardonyx
Sardonyx’s resilience comes from its chalcedony structure and banded density. It should be cleaned with mild soap and warm water.
Ultrasonic cleaning is generally safe, but because of its porous nature, exposure to strong detergents or caustic solutions may affect its surface polish and luster. Always ensure that any engraved or carved surfaces are cleaned gently, using a soft-bristled brush to reach into grooves and bands.
Jewelry Context and Market Trends
August birthstones are increasingly favored in modern jewelry due to their vibrant colors, durability, and symbolic meanings. Their resurgence in popularity has been fueled by both historical appreciation and contemporary design trends.
In recent years, peridot has enjoyed a revival in affordable jewelry and engagement designs, with its lime-green hues being especially popular in stacked rings and ethically sourced collections. The gem is also a favorite of bohemian and naturalistic styles, often paired with gold-filled settings and other earthy gemstones like raw quartz and jasper.
Spinel's versatility and hardness have earned it a place in haute joaillerie, where it is appreciated for its rarity and brilliance. High-quality red or blue spinel is now more accurately identified and valued due to modern gemological advancements. Retailers are increasingly educating consumers on the value of spinel as a durable and affordable alternative to ruby and sapphire.
Sardonyx, though less dominant in mainstream jewelry, is experiencing a niche appreciation in vintage and heirloom markets. Its banded appearance and historical association with sealing rings make it a favorite among jewelry historians and enthusiasts of antique and custom-made pieces.
Conclusion
The August birthstones—peridot, spinel, and sardonyx—represent a unique convergence of geology, history, and symbolism. Unlike many other months that are limited to a single gemstone, August offers three options, each with a distinct allure and purpose. Peridot is a green gem of spiritual clarity and strength, formed in the Earth's depths and believed to hold ancient protective powers. Spinel, once mistakenly used in place of ruby, is a gem of brilliance and durability, now recognized for its rare color variety and affordability. Sardonyx, the original August birthstone, is a stone of layered history and engraved artistry, favored by the ancients for its cultural and symbolic significance.
Whether cherished for their beauty, history, or energetic symbolism, these three gemstones are a meaningful choice for those born in August or receiving a gift inspired by this bright and vibrant month. With their diverse origins, rich histories, and practical care requirements, peridot, spinel, and sardonyx are not just beautiful gemstones—they are timeless symbols of light, protection, and personal connection.