Knowledge Survey Questions - Mineralogy

What characteristics define a "mineral?"
Describe how x-rays can be used to study minerals?
Explain how mineral association can be used to aid in the identification of minerals.

If provided a wooden block model or natural crystal, determine the symmetry elements that are present.

Na, Ca and K substitute for each other in many minerals. Some that come to mind are amphiboles, feldspars and zeolites. Why do these three elements easily replace each other in many minerals?
C (carbon) is typically found in 3-fold coordination. Si (and sometimes Al or Ti) is typically in 4-fold coordination. Al, Ti, Fe, Mg or Mn may be found in 6-fold coordination. Mg, Mn, Na and Ca may be found in 8-fold coordination. Na, Ca and K may have even higher coordination numbers. Explain the variability and what controls it?
Pauling's principle of parsimony says that mineral structures do not, in general, vary greatly. He said that there are limits that control how atoms combine in crystals, and the result is a surprisingly small number of basic structures. In principle, atoms could combine to make minerals in an infinite number of ways, but they don't. Why?
Relate the physical properties of hardness, cleavage, and refractive index to the internal composition and structure of a mineral. In silicate minerals, silica tetrahedra may polymerize in different ways. Contrast and compare polymerization in quartz, feldspar, mica, amphibole, pyroxene, and olivine.
Explain how the progressive substitution of Al+3 for Si+4 in a mineral can lead to the formation of new mineral groups.

There are more than 100 elements and many possible combinations that two or more of these could be combined in minerals. Furthermore, the same combinations of elements could be combined in different structures. Despite this, there are relatively few common minerals. Why?

Explain which tool is better, optics, x-rays, or the SEM, for studying the structure and composition of a mineral.