Aluminum silicate polymorphs

Figure 6.13 The phase diagram for the aluminum silicate polymorphs.

Aluminum Silicate. Al,05 i moi wt 162.05. Ai 33.30%, O 49.37%, Si 17.33%. AljSiOj. Usually contains some water. Polymorphous the three naturally occurring forms are andalusite cyanite. sillimanite. Other aluminum silicate mineral are anauxite, dickite. kaoUttile. kochite, mullite. newtonite, pyrophyllite, takizolite. termierite ton. For prepn and properties see Omelin s Aluminum (8th ed.) 35B, p 313-317 (1934). 

Crystalline mixed oxides of silicon and aluminum exist, called aluminum silicates. They are three polymorphic forms of Al2Si05 (kyanite, andalusite, and sillimanite) and muUite (whose composition ranges between 3AI2O3 2Si02 and 2AI2O3 Si02. Silicon is always tetrahedral while A1 ions is octahedral in... 

Sihcon—oxygen bonds dominate the chemistry of the silicates, silica, and the aluminosihcates.The SiO unit can be linked together to form rings, chains, sheets, and three-dimensional arrays. Asbestos is a generic name for a class of double-chain silicates that, until lately, has been put to a wide variety of uses. SiHca comes in a variety of polymorphs including the optically active a-quartz. Quartz is also piezoelectric. Water glass and siUca gel have a variety of practical appHcations. When aluminum replaces some silicon atoms in a silicate, the aluminosilicates result. These include the zeolites and the micas. 

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