Unit cell of (BN)n, i.e. boron nitride, is similar to that of graphite except that each layer consists of alternating B and B-atoms in hexagonal rings. It crystallises in a hexagonal unit cell with a = 0.251 nm, z = 2 for (BN)n. For graphite, a = 0.2455 nm and distance between C-atoms = 0. 1415 nm. Thus, distance between B and N-atoms is