The effect of hydration and dehydration on the coordination of B in H-Boralite was investigated by 11B magic angle spinning NMR. In hydrated Boralite the quadrupole interaction of B is negligible, implying a highly sym. elec.-field gradient around B due to the 4 O donors to which B is tetrahedrally coordinated. In dehydrated samples a substantial quadrupole interaction for B is found. On dehydration the BO4 tetrahedron is severely distorted. The close agreement with quadrupole parameters of planar BO3 groups in borates and B oxides suggests that in the distorted tetrahedron the B atom is located in the plane between 3 O atoms.