Tourmaline
Chemical Formula	(Ca,K,Na,[])(Al,Fe,Li,Mg,Mn)3(Al,Cr, Fe,V)6(BO3)3(Si,Al,B)6O18(OH,F)4[1][2]
Species	Silicates
Crystal System	Trigonal
Mohs Scale	7
Specific Gravity	2.9-3.1
Color	Most commonly black, but can range from brown, Purple, green, pink, or in a dual-colored pink and green.
Streak	White
Luster	Vitreous, sometimes resinous
Refractive Index	nω=1.635–1.675, nε=1.610–1.650
Cleavage	Indistinct
Fracture	Irregular/Uneven, Conchoidal
Crystal Habit：Parallel and elongated. Acicular prisms, sometimes radiating. Massive. Scattered grains (in granite).