Onyx (black) is a variety of Chalcedony, a member of the Quartz family with a hardness of 7. Its crystal system is hexagonal (trigonal). Onyx is defined as a banded Chalcedony in which the lines of banding are parallel.
Onyx is a stone of inner strength. It enhances one’s endurance and persistence, enabling one to carry even difficult and dreary tasks through to completion. On a mental level, it increases one’s ability to maintain focus, allowing one to learn challenging new material and use well all that one has mastered. It energetically boosts the retention of memory and encourages attention to detail. These traits make Onyx a helpful tool for students, teachers, business owners, accountants, lawyers, software and computer technicians, and all those whose work calls for high levels of focus, perseverance and discipline.
Onyx is also a stone of physical strength. It assists one in containing one’s energies rather than allowing them to dissipate. It helps one to gradually build up one’s vitality. This can be especially helpful after a long illness, or even a prolonged work project, both of which can deplete one’s resources. Onyx emanates the energy of self-mastery. It can help one to control, focus and direct the will, and this brings about a considerable increase in one’s personal power. Onyx cools and condenses excessive energies. It calms nervousness, quells anxiety, soothes hot tempers and brings reason to passion. It is an excellent stone to carry into conflict situations, in which one must maintain a ‘cool head.’
Simmons, Robert; Ahsian, Naisha. The Book of Stones, Revised Edition: Who They Are and What They Teach (several pages). North Atlantic Books. Kindle Edition.