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Figure 6.5 Three different zeolites.
4R
6R
D4R
D6R
Faujasite
(Type X, Y)
Type A
Sodalite
Structure Commission according to a decision of the IZA Council (taken at the
time of the seventh IZC in Tokyo, 1986). These mnemonic codes should not be
confused or equated with actual materials. Structure types do not depend on com-
position distribution of the various possible T-atoms (e.g., Si, Al, P, Ga, Ge, B, and
Be), cell dimensions, or symmetry. The codes are generally derived from the names
of the type materials and they do not include numbers and characters other than
capital Roman letters. Structural criteria alone do not provide an unambiguous
numbering scheme; therefore, to facilitate later additions and simple indexing, the
structure types have been arranged in alphabetical order according to the structure-
type codes. For interrupted frameworks, the three-letter code is preceded by
a hyphen for each structural type, the information given in bold type also includes
the full type name, the maximum topological symmetry (i.e., the highest symmetry
special group), a listing of the topologically distinct T-atoms, their number unit
cell, and the maximum point symmetry of the respective temperature sites
(in parentheses). The reader can get more detailed information in Refs [16
20] .
6.4 Comparison Between Natural and Synthetic Zeolites
Ever since the discovery of stilbite by a Swedish chemist, Cr¨nstedt (1756), a large
number of publications have appeared both on natural and on synthetic zeolites. In
the last century, W¨hler (1848) attempted to recrystallize apophyllite by heating it
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