Onyx is a rich-looking, affordable black stone. It is often mixed with pearls to create elegant jewelry. Onyx, sard, and sardonyx are all varieties of chalcedony (microcrystaline quartz). Onyx comes in brown, white, grey, and black. Sard is a reddish-brown variety. Sardonyx is a blend of sard and onyx with the red bands of sard and the white bands of onyx. If onyx is cleaned with an ultrasonic device or cleaned with abrasive or ammonia based chemicals, discoloration of the stone may occur. Onyx was known to the ancient Greeks and Romans. Use of sardonyx appears in the art of Minoan Crete at Knossos. Egyptians used onyx early as 3000 BC to make bowls and other pottery items.