Well, Onyx is good for nervous system and fight depression, balancing emotion, good for memory, brings confidence . In ancient India, onyx was a symbol of luck.
Obsidian can help to cleanse energetic bio field, stabilizing blood pressure and straighten immune system. This stone will protect owner from making wrong decision and bad behavior. People who wear this stone will not be afraid from any changes in life, good as amulet.
Black tourmaline can create protective aura shield and will reflect all negative stuff. Can positively influence on body and mind. Good for concetration.
Hope it will give you some hints :-) blessed be