Onyx, a protective stone, comes in not only black, but brown, red, black, white and grey. Onyx is a type of quartz found in Brazil, India, California and Uruguay, and is believed to give protection, contain defensive magic, and reduce sexual desires. When used as a healing stone, onyx strengthens and cures diseases of the heart and kidneys, reduces stress and neurological disorders, and improves eyesight.
In ancient Rome, soldiers would wear onyx carved with Hercules or Mars, so that wearer could become just as brave as the depicted God. Black onyx is also believed to be a good stone when breaking an undesirable habit, or being more productive.