Onyx is a form of Chalcedony, a crystal made up of many fine layers of sub-microscopic grains of Quartz. Because of the way these grains stack up in layers Onyx, like Agate (another related Chalcedony) often has colored banding. These layers have made Onyx one of the most popular stones for carving intaglios and cameos.
Onyx has long been associated with magic and for occult purposes it is most commonly the black variety that is used. Some say that is a stone of 'black magic'. It is certainly in tune with the darker and more mysterious side of magic, sorcery and necromancy but to label it as 'evil' is a serious misunderstanding of the stone's energy, which is neutral until influenced by the person who works with the stone. Onyx is said to be a very faithful stone to its owner. It protects against misfortune and illness and prevents illusions, nightmares and confusion caused by evil spirits. Onyx is also reputed to bring unexpected good luck and opportunity to its owner and to protect them from the plots and ill wishes of their enemies. A piece of Onyx, especially a carved sphere, can be kept on your altar or in your meditation room to protect you from unruly energies or warn of impending danger.
Onyx is often used in magic to contact the spirits of Ancestors or the Mighty Dead and can also help you recall memories and visions of your past lives. It is said to soften the barriers between the worlds, allowing you to travel between different planes of existence. Shamanic work with Onyx is often centered around the transition between life and death, and the stone is said to summon friendly spirits who will guide a dying soul on their journey to the next world. Onyx is an excellent stone for students of occult knowledge, helping you to focus on your studies and understand spiritual writings on a deeper level, with your heart as well as your head. Onyx is also believed to help you focus and gain intuitive insights during divination, especially if you are casting stones or bones.