Onyx is a term used for several stones. It has been dyed since ancient time, with the popular pure black variety, being dyed microcrystalline quartz. Its natural color is usually brown, white or grey. And onyx used in architecture isn't a form of quartz at all, but a type of limestone marble. Onyx is very similar to agate. With straight bands of brown, white or black, where agate has curved bands of many colors.

Although regarded as protective, onyx has a reputation as a stone of discord. Onyx was worn to cool the ardors of love, probably because it helps to balance the mind and emotions. Not only avoided by lovers, but also at night, as it provoked nightmares. However, it does improve concentration and devotion, hence many onyx rosaries. Onyx is a strength-giving stone, aiding confidence and useful for athletes or people under stress. Its energy is a mental tonic and can help you cope with fears and worries, making you feel in harmony with your surroundings.