Black Obsidian is very good to use in crystal grids as it is considered to be a grounding stone and a Stone of Manifestation.
Obsidian forms when molten lava quickly cools and is said to be a form of volcanic glass. It shields against negativity and increases and stimulates the gift of prophecy. It is excellent for healing and cleaning out the psyche of negative thoughts and experiences that one has accumulated during course of the day. It helps to release one from resentment of others, fear and anger. It is very grounding, very healing and is also an excellent Stone of Manifestation. A good choice to use daily with an Affirmation.
All our crystals are retuned with vibrational sound and bathed in moonlight in a copper pyramid. Your tumbled stone will arrive with a crystal description card and a drawstring pouch.