Emerald improves the ability to concentrate and raises consciousness.  Because it banishes negative thoughts, promotes self-expression, and restores mental equilibrium, it can also lead to positive action and change.
Emerald promotes health and vigor by eliminating free radicals in the body.  It is said to strengthen and heal the heart and kidneys and to promote circulatory and neurological function.
Emerald increases psychic sensitivity and clairvoyance when held over the third-eye chakra.  Mystics use the stone to gather wisdom from spiritual planes.