Ancient magicians relied upon Black Tourmaline, known as Schorl, to protect them from earth demons as they cast their spells. Today this stone is still revered as a premier talisman of protection, a psychic shield deflecting and dispelling negative energies, entities, or destructive forces.
It guards against radiation and environmental pollutants, and is highly useful in purifying and neutralizing one’s own negative thoughts and internal conflicts, and turning them into positive, usable energy.
Black Tourmaline is also a powerful grounding stone, electrical in nature, providing a connection between Earth and the human spirit. Its supportive energy aligns the energy centers of the body and channels healing light throughout the system.
 
You can read this exerpt and more on black tourmaline at https://www.crystalvaults.com/crystal-encyclopedia/black-tourmaline/