This hand-knotted necklace is made of Sardonyx coins and Baroque Fresh Water Pearls. It's 29 inches long, and finished with a silver-plated lobster-claw clasp.
Sardonyx is a form of stripped Onyx, which in turn is a form of poly-crystalline silica. The color bands can be white, red, tan, or brown, depending on the mineral content of the water present when the onyx is deposited.
Black and white or black and cream Sardonyx has been used for cameos because of the contrast between the white banding and the black matrix, Since Sardonyx is a hard stone (7 -- 7.5 on the Moh's scale), carving a cameo is a pains-taking process. Sardonyx has also has been used for wax seal rings for over 3,000 years.