1. Hassel, O., Norsk. Geol. Tidskrift, 9, 266 (1926).
2. Brager, A., Acta Physicochem. U.S.S.R., 7, 699 (1937).
3. Brager, A., Acta Physicochem. U.S.S.R., 11, 617 (1939).
4. Ewald, P. P., and Hermann, C., “Strukturbericht”, 1, 95 (1931).
5. Goldschmidt, V. M., Norsk. Geol. Tidskrift, 9, 258 (1926).