Other Aluminosilicates that Form Fibers

The zeolites are another structure type of alumino silicate minerals. The eighteenth century identification of this mineral group was made on a few 

The discrepancy in numbers between natural and synthetic varieties is an expression of the usefulness of zeolitic materials in industry, a reflection of their unique physicochemical properties. The crystal chemistry of these aluminosilicates provides selective absorbtion and exchange of a remarkably wide range of molecules. Some zeolites have been called molecular sieves. This property is exploited in the purification and separation of various chemicals, such as in obtaining gasoline from crude petroleum, pollution control, or radioactive waste disposal (Mumpton, 1978). The synthesis of zeolites with a particular crystal structure, and thus specific absorbtion characteristics, has become very competitive (Fox, 1985). Small, often barely detectable, changes in composition and structure are now covered by patents. A brief review of the crystal chemistry of this mineral group illustrates their potential and introduces those that occur as fibers. 

Zeolite minerals are hydrous-aluminum-silicates whose general chemical formula can be expressed as 

The range of the variables can be appreciated from Table 2.7, which presents examples of fibrous varieties from several of the zeolite mineral groups (using the classification system presented by Flanigen, 1977). 

The mineral natroHte (Na2Al2Si30io 2H2O), a member of the group of zeolites that usually occur in acicular or radiating sphemlitc aggregates, has a structure based on four tetrahedra, a four-membered ring, connected in the third dimension by a fifth tetrahedron. The result is a chain (Fig. 2.17A) 

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OTHER CHAIN ALUMINOSILICATES THAT FORM FIBERS... 

From every chemical group mentioned in Dana s System of Mineralogy there are minerals that form as fibers. We began with the most commonly encountered minerals, the silicate and aluminosilicate groups, and now briefly mention a few from other chemical classes. 

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