The most ancient of the August birthstones, sardonyx is a combination of two types of chalcedony (cryptocrystalline quartz): sard and onyx. Bands of brownish red to brown to dark orange sard alternate with typically white or black layers of onyx. In ancient times, sardonyx was a popular stone for Roman seals and signet rings, as hot wax would not stick to it. For millennia, the bands of color in this August birthstone have made it a popular carving material for cameos and intaglios.
Sardonyx is believed to be one of the stones in the High Priest’s breastplate, as referred to in the Old Testament, and to represent the strength of spiritual life. Roman soldiers wore sardonyx rings with the image of Mars carved on them for protection in battle. Today, this August birthstone is associated with courage, happiness and clear communication, bringing stability to marriage and partnerships.