Initial Publication Date: June 28, 2005

Unknown #2

Download and view the crystal structure data

Right click on Unknown_2.cmdf ( 2kB 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).
Start the CrystalMaker program.
Choose the File > Open command, and select the file you just downloaded to view in CrystalMaker.
Click on OK to generate the crystal structure for viewing. You should see something like this...

Determine the identity of the unknown

Using your knowledge of crystallography and systematic mineralogy, and manipulating the downloaded structure in CrystalMaker, answer the following questions to deduce the identity of the unknown. Check your answers by clicking on the "show answer" tabs which appear with each question.

Show question #1

Show answer

Show question #2

To see an adequate portion of the structure (not just the unit cell), choose Transform > Set Range, and click on Expand 7 times to extend the structure along all axes by 70%. Click OK.

Next, click on Edit > Bonding to draw the Si-O bonds. Click on Add and choose "Si" under From and "O" under To. 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 silica tetrahedra, use the Model > Polyhedral command to plot the structure as a polyhedral model).

Show answer