Tourmaline is the name for a large group of borosilicate minerals that vary greatly in color, ranging from opaque, black schorl, to deep pink-red rubellite and translucent green to watermelon-colored elbaite.
The composition of this "kitchen-sink" mineral is given by this formula:
AD3G6 (T6O18)(BO3)3X3Z where
A = Ca, Na, K, Pb or is vacant;
D = Al, Fe2+, Fe3+, Li, Mg2+, Mn2+, Ti;
G = Al, Cr3+, Fe3+, V3+;
T = Si almost exclusively, although there can sometimes be minor Al and/or B3+ substitution.
X = O and/or OH;
Z = F, O and
Discover more about tourmaline HERE (mineralogy & geology; spiritual, metaphysical & healing properties)