Emerald

Composition: a Beryl, Beryllium Aluminum Silicate 
Hardness: 7.5 - 8 
Metaphysical Properties: Loyalty, sensitivity, stone of successful love and domestic bliss.  Enhances memory and mental capacity. Eliminates negativity, and allows one to focus. Brings harmony to all aspects of life. Can help to maintain rhythmic breathing during meditative state. 
Corresponding Astrological signs: Taurus, Gemini, Aries 
Chakra: Heart