Emerald is the "Green" of the Heart Chakra  

Used in Ancient Egypt for healing.  Strenghtens the heart, kidneys, liver, immune and nervous systems.   Stabilizes the personality or the Ego.  i.e. if the Ego is getting out of control.  Amplify’s thought. Alleviates the unknown, hidden fears.  i.e. "I’m afraid but I don’t know what I am afraid of". Uplifting into the higher spiritual insights. 

Unites Souls -  Strengthens relationships  i.e. newly married, new partnerships, new relationships.

Helps with breath and breathing.  Supports pancreas and diabetes (blood sugars).  Supports a Detox.  Strengthens physical eyesight.