Amethyst 
Amethyst is a stone of spiritual protection and purification, cleansing one's energy field of negative influences and attachments, and creating a resonant shield of spiritual Light around the body. It acts as a barrier against lower energies, psychic attack, geopathic stress and unhealthy environments. Relates to the 7th crown chakra and works well with Pisces, Virgos, Aquarius, Capricorns.