The O Stones
Obsidian:  Translucent Black
Magickal Properties:  Protection, Grounding, Divination, Peace, Shielding, Aids in Transitions, Sharpens Vision and Emotional Security.

Olivine:  Green Crystal
Magickal Properties:  Money, Protection, Love and Luck.

Onyx:  Usually Black
Magickal Properties:  Protection, Defensive Magick, Reducing Sexual Desires, Bringing things to the surface in relationships, Retains Physical body strength and Receives and holds vibrations both good and bad.