≈1.5cm to 2cm Tourmaline This mineral forms part of a complex group which include a variety of Borosilicates and Cyclosilicates. Elements that are included in this family include Calcium, potassium, chromium aluminium, sodium, iron and manganese. The crystals in this group do exhibit trigonal structure and have a hardness of 7 on the Mohs scale of hardness. This amazing crystal can be found in a variety of single colours and also in bi, tri and even more complicated colour combinations. Black Tourmaline is by far the most common form of this mineral. Black tourmaline is naturally piezo-electric, which means that it automatically balances positive and negative electrostatic charges. This produces a very calming effect on the user, reducing stress and anxiety, increasing calmness and stillness. Black tourmaline is an excellent stone to use for grounding, creating stability and aiding meditation. This type of tourmaline is also an excellent protection stone. It simply grounds all of us so we are less affected by the moods and thoughts of others. The best way to protect yourself from outside influences is to keep your energy in, and in this stone does that very well.