1. A. V. Nikolaev, Physicochemical Study of Natural Borates [in Russian], Izd. AN SSSR, Moscow (1947).
2. G. Carpeni, Bull. Soc. chim. France, 344 (1949).
3. P. H. Kemp, The chemistry of the borates, P. 1, London (1956).
4. P. H. Hermans, Z. anorgan. und allgem. Chem.,142, 83 (1925).
5. H. Menzel, Z. anorgan. und allgem. Chem.,164, 22 (1927).