Black obsidian is the strongest from obsidian family. It brings brutally out all truth and suppressed feelings. NB! Use only, if you are sure you are ready to look in the mirror and see yourself! Great helper when we need healing from diseases conditioned from suppressed anger (cancer for example). In that case you need to let everything out and let go. Locate on solar plexus, sacral chakra or rootchakra.
Flat stone suits the best for healingwork, because it covers the chakra and the contact surface are is the largest. Also it will not fall off the body and is large enough to draw forth energetic and physical changes. Flat stones are also the best to carry in your pocket.
