Objectives for the topic: Packing, Coordination and Sites

Reading: See syllabus

Images to understand: See syllabus

After completing this topic, the student will be able to:

1. Describe the relative efficiency of random packing, simple cubic packing, cubic close packing, and hexagonal close packing.
2. Describe the difference between hexagonal close packing and cubic close packing.
3. Explain the relevance of packing schemes to mineral structures.
4. Describe the relative number of octahedral vs. tetrahedral sites in a close-packed structure.
5. Define the term coordination number.
6. List the typical coordination number for the following elements (in their typical valence state): Si, Al, Mn, Mg, Fe, Ca, Na, K.
7. Explain the concept of a coordination polyhedron.
8. List the coordination numbers commonly found in minerals.
9. Give the polyhedral name for coordination numbers of: 4, 6, 8.
10. Define a crystallographic site.
11. Explain the ability of different ions to be in the same type of site at different places in a crystal, and how this varies with temperature.
12. Use local charge balance diagrams to understand the bonding in minerals.
13. Describe the relative stability of corner-, edge-, and face-sharing between adjacent polyhedra, and how this varies with the charge on the cation and the coordination number.
14. Explain polyhedral distortion as described in Pauling's Rules, and what causes it.