1. Alexiev, B.: Clinoptilolite des Rhodeopes du nord-est. Bulgare Acad. Sci. Compt. Rendus 21, 10, 1093?1095 (1968)
2. Alietti, A.: Heulanditi e clinoptilolite. Mineral. Petrog. Acta 13, 119?138 (1967)
3. Alietti, A.: Polymorphism and crystal chemistry of heulandites and clinoptilolite. Am. Mineralogist 57, 1448?1462 (1972)
4. Ames, L. L., Jr., Sand, L. B., Goldich, S. S.: A contribution on the Hector, California bentonite deposit. Econ. Geol. 53, 22?37 (1958)
5. Boles, J. R.: Composition, optical properties, cell dimensions and thermal stability of some heulandite group zeolites. Am. Mineralogist 57, 1463?1493 (1972)