Testing the Crystalline Structure of NaCl_(s) - Cubic or Not?

Additional Questions

1. In the internal crystalline structure of NaCl salt, is the cubic structure face-centered or body centered or some other 1:1 configuration?
2. Can we just say that the crystalline structure of salt is cubic or do we have to specify sodium chloride?
3. Can we use table salt as a substitute for pure sodium chloride; i.e., is table salt a pure substance?
4. How do we know the internal crystalline structure of NaCl salt?
5. What is the origin of this knowledge?
6. What kind of evidence is used to determine the internal crystalline structure?
7. What kind of knowledge is gathered from the SEM—empirical or theoretical?
8. What kind of knowledge is used to portray the internal crystalline structure of the salt crystal—empirical or theoretical?