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.
Simmons, Robert. The Book of Stones, Revised Edition (pp. 354-355).