SIMMONS 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. It can keep one focused on an exercise regime, weight loss program or other effort to improve one’s health. Onyx is an excellent stone for body builders, even if the goals are quite modest. It encourages one to stay with the program and facilitates the sense of satisfaction that comes with achieving one’s goals.
Simmons, Robert. The Book of Stones, Revised Edition (pp. 354-355).