1. Khrushchev, M.M. and Berkovich, E.S., Mikrotverdost’ opredelyaemaya metodom vdavlivaniya (Determination of Microhardness by Indentation), Moscow: AN SSSR, 1943.
2. Mott, B.A., Micro-Indentation Hardness Testing, London: Butterworths, 1956.
3. GOST 21206-75, Moscow: Gostandart SSSR, 1975.
4. Musyal, S.A., Microhardness and Microbrittleness as Possible Classification Parameters of Fossil Coals, Petrograficheskie osobennosti i svoistva uglei (Petrographic Peculiarities and Properties of Coals), Moscow: AN SSSR, 1963.
5. Hower, J., Trinkle, E.J., and Raione, R.P., Vickers Microhardness of Telovitrinite and Pseudovitrinite from High Nolatile Bituminous Kentucky Coals, Int. J. Coal Geology., 2008, vol. 75.