Smoky Quartz is THE protection stone. It provides deep protection and transmutation of all kinds of negative energies. It purifies places, spaces, and auras. Some say the reason it has its smoky color is that when it was formed, it absorbed and trapped all the negative energies of the world around it. Keep a piece by your front door and also where you sleep to ensure sweet dreams. Smoky Quartz takes in whatever is negative or of a low vibration, and holds that energy away from you.
However you use your crystal, may its energies serve you well. Be sure to cleanse regularly.
