Malachite is particulary effective protection stone. It relieves pain and removes all negative energy. Powerful healer for heart, but with physicly sick heart it might be a little too strong, in that case use together with selenite. Specially nice for pregnant woman, protects the baby in the womb and helps to relieve pain while giving birth.
Never cleanse with water or salt, the best ways are with sound (tibetan bells), on candlelight or with incense.
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.