The thermal behavior of fully Sr-exchanged LTA- and FAU-framework zeolites was followed in the temperature. range from ambient to 1500 degrees C. Both zeolite frameworks collapsed into amorphous intermediate substances after heating between 780 and 950 degrees C. Prolonged annealing of these products above 950 degrees C induces their recrystallization to ordered hexagonal SrAl2Si2O8, [a(0) = 5.1970(2) Angstrom, c(0) = 15.200(1) Angstrom] and disordered hexagonal Sr(0.85)square(0.15)Al(1.71)Si(2.29)O(8) [a(0) = 5.2039(2) Angstrom, c(0) = 15.158(1) Angstrom], diphyllosilicate phases, respectively. These phases are unstable under prolonged heating, and near 1100 degrees C, they can be polymorphously transformed into corresponding Sr-feldspar(LTA) [a(0) = 8.358(2) Angstrom, b(0) = 12.941(3) Angstrom, c(0) = 7.114(1) Angstrom, beta = 115.26(2)degrees] and Sr-feldspar(FAU) [a(0) = 8.354(2) Angstrom, b(0) = 12.957(3) Angstrom, c(0) = 7.128(2) Angstrom, beta = 115.27(2)degrees] phases, maintaining framework cation-ordering characteristics. The phase conversions in the temperature range investigated were followed by thermal (DTA, TGA, and DSC), XRPD, and SEM analyses. The structural mechanism for M1-xAl2-2xSi2+2xO8 (M = Ca, Sr, Ba, Pb) polymorphous transformation from diphyllosilicate to feldspar topology is discussed.