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2. I. Naray-Szabo, Inorganic Crystal Chemistry, Adler's Foreign Books.
3. A. S. Povarennykh, The Crystal-Chemical Classification of Mineral Forms [in Russian] Naukova Dumka, Kiev (1966).
4. E. Kordes, Optische Daten, Verlag Chemie, GMBH, Weinheim Bergstr. (1960).
5. S. S. Batsanov, Structural Refractometry [in Russian], Izd-vo MGU, Moscow (1959).