1. Brazhkin, V.V., Lyapin, A.G., and Hemley, R.J., Harder than Diamond: Dreams and Reality, Philosop. Mag. A, 2002, vol. 82, no. 2, pp. 231–253.
2. Polyakov, V.P., Nozhkina, A.V., and Chirikov, N.V., Almazy i sverkhtverdye materialy (Diamonds and Superhard Materials), Moscow: Metallurgiya, 1990.
3. Povarennykh, A.S., Tverdost’ mineralov (Hardness of Minerals), Kiev: Izd. AN UkrSSR, 1963.
4. Sinteticheskie sverkhtverdye materialy (Synthetic Superhard Materials), 3 vols., vol. 1, Synthesis of Superhard Materials, Kiev: Naukova Dumka, 1986.
5. Gao, F.M., He, J.L., Wu, E.D., et al., Hardness of Covalent Crystals, Phys. Rev. Lett., 2003, vol. 91, no. 1, pp. 015502 1–4.