Tourmaline (dravite) from a layered two-plagioclase anorthosite in the Boehls Butte quadrangle, Idaho, has the following structural formula: (Na0.55Ca0.17)0.72(Mg1.96Fe0.57Mn0.01Ti0.04V0.03Al0.47)3.08Al6(BO3)3.02Si5.98O18(OH,F)3.35. The indices of refraction are ω = 1.647(1) and ε = 1.621(1), and the unit cell parameters are a = 15.9425(6) and c = 7.1883(3).