Powers: Protection, grounding, divination, peace
Magical/ritual lore: Obsidian is simply lava that cooled so fast that the minerals contained within didn’t have time to form. It is a naturally occurring glass.
Magical uses: Obsidian is a grounding, centering stone. Hold it in your hands or place your bare feet on two small, polished pieces when you’re flighty or can’t seem to get your physical life in order. Remember- the physical is the path to the spiritual. Each is a reflection of the other.
Obsidian is effective when carried or used in protective rituals. One involves surrounding a white candle with four obsidian arrowheads that each point to one of the directions. This sets up aggressive energies that guard the place in which it is set up.
Spheres of obsidian, still fashioned in Mexico, are fine scrying tools. If you don’t have good results scrying with quartz crystal, try a piece of sphere of obsidian. For some, the blackness of the stone allows easier access to the subconscious mind.
(Source: Cunningham’s Encyclopedia of Crystal, Gem, and Metal Magic)