Onyx, silicon dioxide, is a banded chalcedony, usually with white streaks alternating with black. White alternating with brown streaks is sard-onyx and white with red is carnelian-onyx. Onyx may also be cut as a solid color when the banding is very thick. It works well in conjunction with pearl or diamond.
There are several varieties of “onyx” which are not actually onyx. Mexican Onyx is actually a steaked or banded calcite which is far too soft for jewelry. Brazilian onyx, Algerian onyx, Yava onyx, cave onyx, and onyx marble are all misleading names referring to stalagmite calcite. Onyx may also be dyed to make dull colors glossy black by applying a burnt sugar treatment and then sulfuric acid. This may cause the stone to fade later on however.
It was thought in the seventeenth century that an onyx ring might render its wearer invisible. Perhaps this stems from its connection to darkness, its blackness giving rise to many superstitions. In China, miners feared to mine it and sent menials into the mines to bring it out instead. A thirteenth century text even alleged that the stone carved in the likeness of a camel or two goats would cause horrible dreams. Others claimed the stone caused quarrels, especially between married couples, because of the opposing colors representing the two sexes. The people of India and Egypt believed that it could be worn about the neck to cool the fervor of love even to the point of driving the two lovers apart. The Arabs call onyx el jaza “sadness” and claim it causes nothing but discord and melancholy.
Onyx was not only used as protection from evil witchcraft and enchantments, it could also control undesirable thoughts and bad tempers. It was thought the stone allowed wounds to close and assisted in childbirth. This is an old Pagan belief adopted by the Christian Church. The Abbey Church of St Alban holds a healing onyx engraved with the image of Aesculapius, the Roman god of medicine. Black onyx was once highly prized for rosary beads, which may be why it is considered good for stress and the banishment of grief.