Sardonyx: The Original August Birthstone with 4,000 Years of History

A gemstone curator's guide to August's original birthstone, its banded beauty, and why collectors still seek it out.

If you ask most people to name August's birthstone, they will say peridot. Some gemstone enthusiasts might add spinel. But the original August birthstone, the one listed in 1912 when the American National Association of Jewelers first standardized the birthstone chart, was sardonyx.

I have been sourcing gemstones for over a decade, and sardonyx is one of those stones that teaches you to look beyond sparkle. It does not flash or shimmer. Instead, it pulls you in with precise, layered bands of reddish-brown and white that look almost painted by hand. It is a gemstone built for carving, for storytelling, and for people who appreciate history as much as beauty.

This guide covers everything you need to know about sardonyx: its ancient roots, what makes it unique among chalcedony varieties, where it comes from, and why it still deserves a place in the August birthstone conversation.

4,000 Years of History

Sardonyx has one of the longest documented histories of any gemstone. Ancient civilizations prized it not as a decorative stone but as a functional one, valued for its layered structure that made it ideal for detailed carving.

Roman soldiers wore sardonyx rings and talismans engraved with images of Mars, the god of war. They believed these carvings granted courage in battle and protection from harm. The stone became one of the most popular materials for cameos and intaglios (engraved seals used to stamp wax on official documents). Its naturally layered bands made it perfect for relief carving: artisans could carve a white figure against a dark reddish-brown background, all within a single stone.

The tradition extended well beyond Rome. Sardonyx appears in biblical references as one of the stones set in the breastplate of the high priest. Throughout the Renaissance, European gem cutters continued the Roman tradition of carving elaborate cameo portraits and mythological scenes into sardonyx. The city of Idar-Oberstein in Germany became a global center for agate and sardonyx cutting, a reputation it maintains to this day.

By the time the 1912 birthstone list was formalized, sardonyx had been treasured for roughly four millennia. It earned the August spot on pure historical weight.

What Is Sardonyx, Exactly?

Sardonyx is a banded variety of chalcedony, the same mineral family that includes agate, carnelian, and onyx. Its name is a straightforward combination of its two components: sard (a brownish-red chalcedony colored by iron oxide) and onyx (chalcedony with parallel bands, typically black or white).

What sets sardonyx apart from other banded agates is the specific color combination. The reddish-brown sard layers alternate with white or black onyx layers in parallel, well-defined bands. This crisp contrast is what made the stone so valuable to ancient carvers and what continues to give it visual impact today.

If you are familiar with carnelian (the orange-red chalcedony), sardonyx is essentially its banded cousin. Where carnelian is a solid, uniform color, sardonyx displays dramatic stripes. The iron oxide content determines the depth of the reddish-brown tones, ranging from warm honey to deep chocolate.

All of these stones (sardonyx, carnelian, agate, and onyx) are varieties of microcrystalline quartz. They share similar hardness and durability but differ in color, pattern, and how they formed within volcanic rock cavities millions of years ago.

Where Sardonyx Comes From

Sardonyx forms in volcanic and sedimentary rock environments where silica-rich solutions slowly deposit layers of chalcedony over millions of years. The alternating conditions during formation create the distinctive banding patterns.

The major sources include:

• India has been the primary traditional source for centuries, producing stones with particularly vivid reddish-brown and white contrast.
• Brazil yields large quantities of banded chalcedony, including high-quality sardonyx specimens.
• Germany, specifically the Idar-Oberstein region, has been a historic center for agate and sardonyx cutting since the Roman era. While much of the raw material is now imported, the cutting expertise remains world-class.
• Uruguay produces excellent agate and sardonyx, often alongside amethyst geodes.
• United States, particularly in Oregon and parts of the Southwest, produces collectible sardonyx specimens.
• Madagascar has become an increasingly important source for a range of chalcedony varieties, including sardonyx.

Why Peridot Replaced Sardonyx

The story of sardonyx losing its August birthstone spotlight follows a pattern I have seen with other traditional birthstones. The history of birthstones is full of these shifts, and the reasons usually come down to changing consumer expectations.

Sardonyx is stunning in carvings and cabochons, but it does not have the transparent, faceted sparkle that modern jewelry buyers have come to expect. It is an opaque stone. You cannot facet it into a brilliant cut that catches light from across the room.

Peridot, with its bright lime-green color and ability to take a beautiful faceted cut, offered exactly what the modern market wanted: a transparent, sparkling gemstone in a distinctive color. It became the commercially dominant August birthstone. More recently, spinel was added as a third August birthstone in 2016, giving August babies even more options.

But sardonyx was never "replaced" in the official sense. It remains a recognized August birthstone. The shift was cultural and commercial, not a formal demotion. For collectors who value historical significance, artistic heritage, and the quiet beauty of banded stone, sardonyx is still the definitive August gemstone.

Evaluating and Caring for Sardonyx

What to Look For

The most valued sardonyx specimens display well-defined, high-contrast bands with vivid reddish-brown and clean white layers. Uniform, parallel banding is the gold standard. Stones where the color transitions are sharp rather than blurry command the highest appreciation from collectors and carvers alike.

The depth of the reddish-brown sard layers matters as well. Rich, warm tones with good saturation are preferred over muddy or washed-out browns. In carved pieces, look for how skillfully the artist used the natural banding to create contrast between the foreground and background of the design.

Durability

Sardonyx rates 6.5 to 7 on the Mohs hardness scale, making it durable enough for most jewelry applications. It is comparable to quartz in toughness, meaning it resists scratching well and can handle everyday wear in rings, brooches, and pendants.

Care and Cleaning

Warm soapy water and a soft brush are all you need. Avoid ultrasonic cleaners and harsh chemical solutions, as these can damage the stone's surface or affect any treatments. Store sardonyx jewelry separately from harder gemstones like sapphires or diamonds to prevent scratching.

Common Jewelry Settings

Sardonyx has traditionally been popular in men's jewelry: signet rings, cufflinks, and tie bars. It also appears in brooches, carved pendants, and statement rings. The banded pattern makes each piece unique, which is part of its appeal for collectors who want something that stands apart from mass-produced faceted gemstone jewelry.