STRUCTURE REFINEMENT OF K-EXCHANGED NATROLITE BY RIETVELD METHOD.

The crystal structure of K-exchanged natrolite is refined by the Rietveld analysis of X-ray powder diffraction data. The K-exchanged form is obtained by the treatment of natural natrolite (Yanai, Aichi Pref. , Japan) with KCl solution at 130 degree C for 7 days. The degree of K-exchange is 98. 6%, and its chemical composition and lattice parameters are; K//1//5//. //8Na//0//. //2(Al//1//5//. //7Si//2//4//. //2O//8//0) multiplied by (times) 20. 6H//2O, a equals 19. 3137 (2) Angstrom, b equals 19. 7672 (2) Angstrom, c equals 6. 48206 (6) Angstrom. In the K-form, the rotation angle psi of the framework projected along c is 13 degree , being 11 degree smaller than that of natrolite ( psi equals 24 degree ). This causes about 6% increase in both a and b parameters. On the other hand, c parameter becomes shorter by about 2% due to the twisting of the framework by the rotation of the tetrahedra around an axis normal to c. In the K-form K atoms and H//2O molecules are situated near the sites of H//2O molecules and Na atoms in natrolite.