Structure of Topaz

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

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Topaz, Al2(SiO4)(OH,F)2  differs from andalusite, kyanite and sillimanite in having one oxygen in the formula replaced by hydroxyl or fluorine. Below is a ball model of one layer, with blue representing oxygen, yellow aluminum and magenta, silicon.

The polyhedral model below shows several layers. Fluorine and hydroxyl substitution occurs in alternate layers, as shown by the red balls. The layers are close-packed but have an ABAC scheme, and thus the structure is neither cubic nor hexagonal close-packed.

The diagram below shows a more complete view of the layers.

Below is a ball model. Oxygen is shown in shades of blue, hydroxyl and fluorine in green, aluminum in yellow and silicon in purple.

 

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Created 22 February 2002, Last Update

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