For each of the crystal structures listed on the next page, follow the instructions to download the structure from the appropriate online database. Then follow the instructions for viewing the structure in the appropriate viewer (e.g., XtalDraw, CrystalMaker, or a website-specific Java applet).
When manipulating the crystal in the viewer,
- Note how many different types of atoms represented in each structure (the different colored balls or polyhedra).
- Determine what other atoms are "in the neighborhood" and how many nearest neighbor atoms are in the structure.
- Check to see if each cation is in an electronically neutral environment (or nearly so).
- Note the relative lengths and angles of the chemical bonds.
- For minerals with oxygen as the dominant anion, look for close-packed arrays or oxygens.
- Look for coordination polyhedra and ways in which these polyhedra come together to form the overall structure.
- Look for regular repetitions of atoms or groups of atoms (i.e., symmetry).