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An August birthstone, the sardonyx gemstone, combines alternating layers of sard and onyx鈥攖wo types of the layered mineral chalcedony鈥攖o create a reddish zebra-striped gemstone with white bands.

Its name, similarly, combines聽sard聽(referencing the ancient Persian city, Sardis鈥攊n present-day Turkey鈥攚here the red stone was found) with聽onyx聽(from the Greek word of the same spelling, which meant 鈥渘ail or claw.鈥�)

Sard ranges in color from yellowish-red to reddish-brown, depending on how much iron oxide is present. Sard is easily confused with carnelian, another type of chalcedony that is slightly softer and lighter in color. The deep red, brown, and yellow color of this stone makes sardonyx jewelry stand out.

Sardonyx, like onyx, shows layers of parallel bands instead of the chaotic, curved bands that compose agate, another type of chalcedony.

The finest examples of sardonyx, which display sharp contrasts between layers, are found in India. Other sources include Brazil, Germany, Czech Republic, Slovakia, Madagascar, Uruguay, and the United States.

Measuring 6.5 on the Mohs hardness scale, sardonyx is widely available and relatively inexpensive as gems, beads, and jewelry. It is often carved into cameos, intaglios, and brooches to show the color contrast between layers.