Smokey Quartz is associated with the solar plexus chakra, and known as an excellent ground stone. Many believe it aids in relieving stress and anxiety, while calming a hyperactive mind. Smokey Quartz is also said to disperse fear and lift depression and negativity, while encouraging positive thought and action. Others associate the stone with detoxifying the digestive system, and protecting against radiation. Typical colours are Brown and Black.
Chakras - Base Chakra, Solar Plexus Chakra 
Zodiac - Scorpio, Capricorn 
Element - Earth/Air