Being born out of lava, black obsidian has the potent energy of the interaction of several raw elements, including fire, earth, and water. It's categorized as volcanic glass and is very hard and smooth, but it can have incredibly sharp edges.
Obsidian has been used throughout history for various tools, such as knives and arrows. It has even been experimented with for surgical scalpel blades, and in some cases it's actually sharper than a metal blade.
Black obsidian crystal balls and polished mirrors are used in various cultures for deep healing purposes. They're believed to help a person become more grounded, focused, and clear in all practical matters. They also can assist in developing razor-like mental abilities and the power of discernment.
Because black obsidian expresses a clear energy of truth without taking any sides, it can be useful for those who tend to react emotionally to people and events. A piece of black obsidian jewelry—be it a ring or a bracelet—can help anchor erratic energies, bring more balance to one's life, and clear one's mind of fears and distractions.