1. Framework Silicates (cont.)
Mineral Al subst. Openess of structure
Silica minerals none Tight; only trace interstitial
atoms
Feldspars 1:3 to 2:2 Open enough to allow
interstitial K+, Na+ or Ca2+
Feldspathoids ≥1:3 Open enough to allow
Scapolites variable Same as above plus OH-,
Cl-, CO32- or SO42-
Zeolites ≥1:3 Contain continuous channels through the
structure, as well as cations
plus H2O

2. Feldspathoid group

3. NaAlSiO4, hexagonal, space group: P63
Nepheline
NaAlSiO4, hexagonal, space group: P63

4. Nepheline (Na,K)AlSiO4

5. Leucite KAlSi2O

6. Scapolite series Marialite 3(NaAlSi3O8) x NaCl
Meionite 3(CaAl2Si2O8) x CaSO4

7. Zeolites
Framework
Silicates

8. Analcime
NaAlSi2O6(H2O)

9. Sodalite
Na8(AlSiO4)6Cl2

10. Chabazite, Ca2[Al2Si4O12](H2O)6

11. Heulandite
Ca[Al2Si7O18](H2O)6

12. Heulandite

13. Fibrous Zeolites, e.g. Natrolite

14. Natrolite
Na2[Al2Si3O10](H2O)2

15. Properties of zeolites
High degree of hydration
Low density and large void volume when dehydrated
Stability of the crystal structure when dehydrated
Cation exchange properties
Uniform and exact defined molecular channels
Ability to absorb gases
Catalytic properties

16. Main applications of Zeolites:
Molecular Sieve, Catalysis, Ion-exchanges