If you are attending the TRIAD crystalline Masterclass then I recommend that you grad 2 of obsidian, ammonite and indigo gabbro for a room size 3.5m square or 4 of each for a 6m square room.

If you have a larger space then I would get the selenite pyramid to assist in the further meters you need to cover.

Obsidian is one of the most powerful stones for psychic protection and clearing entities of spirits. You will be using this to also clear any dirty or stuck energy and stress in your body or home.