Unknown #8

Download and view the crystal structure data

1. Right click on Unknown_8.cmdf ( 12kB Dec16 09) to download the crystal structure to your computer. (This file was modified from a CIF file in the Crystal Structure Library provided in CrystalMaker).
2. Start the CrystalMaker program.
3. Choose the File > Open command, and select the file you just downloaded to view in CrystalMaker.
4. Click on OK to generate the crystal structure for viewing. You should see something like this...
   

Determine the identity of the unknown

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Click on Edit > Bonding to draw the Si-O bonds. Click on Add and choose "Si" under From and "O" under To. Follow the same procedure for adding the Al-O bonds. Clicking on the box under Info will give you information about coordination. Finally, click on OK to draw the bonds. The window should look like this...

Are the silica tetrahedra isolated or connected in some way? If connected, how? (hint: to highlight the tetrahedra, use the Model > Polyhedral command to plot the structure as a polyhedral model).

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The silica tetrahedra are linked in a 3-dimensional network, making this mineral a tectosilicate.