Boron is an essential constituent of tourmaline. The source of
boron can be from fluids or other boron bearing minerals and must
be concentrated by geochemical processes in order to form tourmaline,
as it is a trace constituent in the upper crust, lower crust
and mantle. Formation of tourmaline is strongly influenced by
boron content within the protolith and fluids interacting with
crustal rocks during metamorphism (Henry and Dutrow, 1996).