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Natural Zeolites - Definition
A Collectors Perspective
 Volker Betz, Taunusstein, Germany

Since the introduction of the term Zeolite by Cronstedt in 1756, it was discussed and used in different ways.  Until a general acceptance as a „Family“ of alumosilicates with water content, there was a debate of about 100 years. The present definition published in a paper by Coombs et al. (1997) is given at right. This replaced a previous definition which restricted the term to only alumosilicates with a water content. Now also water free and frame-works with other elements than Si and Al are Zeolites.

Many minerals former (in 19thCentury) belonging to Zeolites - like Apophyllite - do not have a zeolite framework and are not Zeolites.

Definition: A zeolite mineral is a crystalline substance with a structure characterized by a framework of linked tetrahedra, each consisting of four O atoms surrounding a cation. This framework contains open cavities in the form of channels and cages. These are usually occupied by H2O molecules and extra-framework cations that are commonly exchangeable. The channels are large enough to allow the passage of guest species. In the hydrated phases, dehydration occurs at temperatures mostly below about 400°C and is largely reversible. The framework may be interrupted by (OH,F) groups; these occupy a tetrahedron apex that is not shared with adjacent tetrahedra.


© 2009  by Volker Betz , all rights reserved