Sardonyx semiprecious gemstone index and mineral information

Sardonyx is a variety of agate with reddish-brown and white bands. It is a member of the layer stones. Sard is the brownish-red variety of chalcedony. Sardonyx has straight bands of white, together with bands of brownish red sard thus, the name sardonyx. Sard takes its name from the Greek “Sardis,” the capital of ancient Lydia. Until the middle Ages sard shared the name “sardion” with carnelian. Sard forms from the deposition of silica at low temperatures from silica-rich waters percolating through cracks and fissures in other rocks. The layer stones are: onyx, sard onyx, cornelian onyx, and niccolo. Usually they are cut from agates or other chalcedonies with even parallel layers, a lighter layer above a darker one.

Sardonyx exists naturally, but a large amount is produced by staining agate, which is called “banded agate.” It was once considered more valuable than silver or gold. Today, sardonyx is relatively common and inexpensive; normally it is cut en cabochon and can be made to resemble an eye. It is used for jewelry such as cameos, beads, brooches and small statuary.

Ancient Egyptians wore sardonyx as a talisman. Romans also believed that it gave courage when going into war and in Renaissance Europe, wearing a sardonyx stone was believed to bestow eloquence on speakers.

Sardonyx is found in India where it has been mined since ancient times. It still remains a major source. It is also found in the Ural Mountains of central Russia, and in the United States in Tampa Bay, Florida, and El Paso County, Texas. Major deposits of sard are found in Ratnapura, Sri Lanka. Other sources are India, Brazil, and Uruguay.

Sardonyx is one of the twelve gemstones of the ceremonial breastplate worn by the high priest Aaron, representing the twelve tribes of Israel as described in the Old Testament book of Exodus, and is also known as the month of August’s birthstone meaning, satisfaction.

Mohs’ hardness: 6.5