August Birthstones: Peridot, Spinel & Sardonyx; Which One is Right for You?

August claims three official birthstones — more than any other month. Peridot, spinel, and sardonyx each bring a distinct character, from peridot's volcanic green to spinel's rainbow range to sardonyx's banded warmth.

Peridot: The Volcanic Gem

Peridot is the gem variety of olivine, a mineral that forms deep in the earth's mantle and arrives at the surface through volcanic eruptions. It's one of the few gemstones that exists in only one color: green. The shade ranges from yellow-green to olive to rich chartreuse, depending on iron content.

What makes peridot mineralogically fascinating is its origin story. Some peridot crystals arrive on earth inside meteorites — pallasites, specifically, which are stony-iron meteorites containing olivine crystals suspended in a nickel-iron matrix. These extraterrestrial peridots are among the rarest gemstones on earth.

The most important terrestrial source is the San Carlos Apache Reservation in Arizona, which produces about 80% of the world's commercial peridot. High-quality specimens also come from the Suppat Valley in Pakistan and Zabargad Island in Egypt's Red Sea — the original historic source, mined since 1500 BCE.

Peridot Facts

Spinel: The Underrated Gem

For centuries, the world's most famous "rubies" were actually spinels. The 170-carat Black Prince's Ruby in the British Imperial Crown? Spinel. The Timur Ruby, a 361-carat stone inscribed with the names of Mughal emperors? Also spinel.

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Spinel was only added as an August birthstone in 2016 by the American Gem Trade Association, correcting centuries of underappreciation. This magnesium aluminum oxide (MgAl₂O₄) occurs in virtually every color: red, pink, blue, violet, orange, and black.

The most prized variety is "cobalt blue" spinel from Vietnam and Sri Lanka, which produces an intense, neon-like blue rivaling the finest sapphires. Red spinel from Myanmar's Mogok region and Tanzania's Mahenge deposits can rival ruby in color saturation at a fraction of the price.

Sardonyx: The Layered Stone

Sardonyx is a banded variety of chalcedony combining alternating layers of sard (reddish-brown) and onyx (white to black). It's been prized since antiquity for cameo carving — the contrasting layers allow artisans to carve raised white figures against dark backgrounds.

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Roman soldiers wore sardonyx rings carved with Mars or Hercules into battle. The stone was believed to bestow courage and eloquence — a practical combination for military leaders who needed both.

Today, sardonyx is one of the most affordable semi-precious stones, making it an accessible entry point for August-born collectors. Quality specimens show sharp, well-defined bands with strong color contrast.

Collecting August Birthstones

Each of August's three birthstones offers a different collecting experience:

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Peridot is best collected as faceted gems or raw crystal specimens. Large, clean peridot crystals from Pakistan are particularly stunning as display pieces.

Spinel is a gem collector's stone — undervalued relative to its beauty and rarity. Fine spinels in unusual colors (hot pink, cobalt blue, orange) are excellent investments.

Sardonyx shines as carved objects and vintage cameos. Estate jewelry featuring sardonyx cameos connects you to thousands of years of lapidary tradition.

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Comparing the Three August Birthstones

August is the only month with three distinct birthstones spanning three entirely different mineral groups. Understanding their differences helps you choose the right one.

Peridot Identification and Buying Tips

When selecting peridot, color is the primary value factor. The most desirable shade is a rich, saturated green without visible brown or yellow overtones. Peridot has a characteristic oily or greasy luster that distinguishes it from emerald or green tourmaline. Most peridot has visible inclusions (called "lily pads" for their distinctive disc-like shape), which are accepted in the trade. Eye-clean specimens command premium prices.

Be aware that peridot can be confused with green tourmaline or chrome diopside. Peridot's double refraction (you can see doubled facet edges when looking through the stone with magnification) is a reliable identifier.

Spinel: The Gem Collector's Favorite

Spinel (MgAl₂O₄) forms in marble through contact metamorphism and in alluvial deposits. Its cubic crystal system gives it a natural octahedral habit, producing beautifully formed crystal specimens. Spinel's hardness of 8 (equal to topaz) makes it extremely durable for jewelry.

Key spinel varieties for collectors:

• Cobalt blue (Vietnam, Sri Lanka): Intense neon blue caused by cobalt. Among the most expensive spinels.
• Hot pink (Mahenge, Tanzania): Vivid pink to red, sometimes with a neon quality. Mahenge spinel has exploded in popularity and value since the 2007 discovery.
• Red (Mogok, Myanmar): The classic "Balas ruby" color. Fine red spinel can rival ruby in beauty at a fraction of the cost.
• Lavender/gray: Subtle, sophisticated colors gaining popularity with designers.

Sardonyx: History's Favorite Carving Stone

Sardonyx has been continuously used in jewelry and decorative arts for longer than almost any other gemstone. The Romans perfected the art of sardonyx cameo carving, taking advantage of the stone's alternating red-brown (sard) and white (onyx) layers to create intricate raised relief portraits and scenes. This tradition continues today, particularly in Idar-Oberstein, Germany, which has been a center for agate and sardonyx carving since the 15th century.

Sardonyx forms in volcanic rocks where silica-rich fluids fill cavities and deposit alternating layers of chalcedony with different iron oxide content, creating the banding pattern. India, Brazil, Germany, and Madagascar are the primary sources.

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Caring for August Birthstones

Each August birthstone has different care requirements based on its hardness, cleavage, and chemical stability.

Peridot Care

Peridot's Mohs hardness of 6.5-7 makes it moderately durable but softer than quartz (7), meaning it can be scratched by sand, dust, and many common surfaces. Clean peridot with warm soapy water and a soft brush only. Never use ultrasonic cleaners, as peridot commonly contains small inclusions that can fracture under vibration. Avoid steam cleaning as well. Peridot is sensitive to rapid temperature changes and strong acids. Store separately from harder gemstones like sapphire, garnet, and quartz to prevent surface abrasion.

Peridot's green color is caused by iron in the crystal structure and is stable in light. Unlike many green gemstones, peridot will not fade from sun exposure, making it safe for display in bright rooms.

Spinel Care

Spinel is one of the most durable and care-free gemstones available. At Mohs 8 with no cleavage, spinel is harder than tourmaline, garnet, and topaz. It can be cleaned with warm soapy water, ultrasonic cleaners, or steam cleaning. Spinel's colors are stable in light and heat. It is an excellent choice for everyday jewelry, including rings. The only precaution: as with any gemstone, avoid extreme impacts that could cause chipping.

Sardonyx Care

Sardonyx (Mohs 6.5-7) is durable enough for most jewelry applications. As a chalcedony variety, it has excellent toughness (resistance to breaking) due to its microcrystalline structure. Clean with warm soapy water. Sardonyx is slightly porous, so avoid prolonged soaking, strong chemicals, and contact with dyes or oils that could be absorbed. Sardonyx is stable in light and safe for display anywhere.

Building a Birthstone Collection

Collecting all twelve months' birthstones is a popular and rewarding approach to building a crystal collection. Each month adds a new mineral family and a new color to your display. For August, the three-stone representation (peridot's green, spinel's range, sardonyx's bands) gives you one of the most visually diverse months in the birthstone calendar.

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Frequently Asked Questions

Which August birthstone is the best for jewelry?
Spinel (Mohs 8, no cleavage) is the most durable and therefore the best for everyday jewelry, including rings. Peridot (Mohs 6.5-7) is suitable for earrings, pendants, and occasional-wear rings but requires more care. Sardonyx (Mohs 6.5-7) is best for carved pieces, cabochons, and statement jewelry rather than delicate faceted designs.

Is peridot from meteorites available to buy?
Pallasite meteorite specimens containing olivine (peridot) crystals are available from meteorite dealers and some gem shows. They are significantly more expensive than terrestrial peridot due to their extraterrestrial origin and scientific significance. Most specimens are sold as slices or thin sections that show the olivine crystals suspended in the nickel-iron matrix, often backlit to display the green color.

Why was spinel only recently added as an August birthstone?
Spinel was not recognized as a separate species until relatively modern gemological advances. For centuries, fine red spinels were classified as rubies, and blue spinels were called sapphires. As gem identification technology improved, spinel earned its own identity and appreciation. The American Gem Trade Association added spinel as an August birthstone in 2016, finally giving this historically misidentified gem its due recognition.