2    a.   (TiO₂): Ti-O  CN= 6, ev = 2/3     therefore there are 6 O surrounding each Ti with
                             octahedron coordination and 3 Ti around each O with equilateral triangle co-
                             ordination

                (MgCO₃): Mg-O  CN = 6, ev =1/3---C-O  CN = 3, ev = 4/3       therefore there
                                  are 6 O surrounding each Mg with octahedron coordination, 3 O around
                                  each C with equilateral triangle coordination and 2 Mg and 1 C
                                  surrounding each O with equilateral triangle coordination

                (PbSO₄):    Pb-O  CN = 8, ev = 1/4---S-O  CN = 4, ev = 3/2       therefore there
                                  are 8 O surrounding each Pb with cube coordination, 4 O surrounding 
                                  each S with tetrahedron coordination, and 2 Pb and 1 S surrounding each
                                  O with equilateral triangle coordination

                (ZnCO₃):    Zn-O  CN = 6, ev = 1/3---C-O  CN = 3, ev = 4/3      therefore there are
                                  6 O surrounding each Zn with octahedron coordination, 3 O surrounding
                                  each C with equilateral triangle coordination, and 2 Zn and 1 C sur-
                                  rounding each O with equilateral triangle coordination

                (MnO₂):    Mn-O  CN = 6, ev = 2/3        therefore there are 6 O surrounding each
                                 Mn with octahedron coordination and 3 Mn surrounding each O with
                                 equilateral triangle coordination

                (NaNO₃):    Na-O  CN = 6, ev = 1/6---N-O  CN = 3, ev =  5/3       therefore there
                                   are 6 O surrounding each Na with octahedron coordination, 3 O sur-
                                   rounding each N with equilateral coordination, and 2 Na and 1 N sur-
                                   rounding each O with equilateral triangle coordination

                (Mg2SiO₄):   Mg-O  CN = 6, ev = 1/3---Si-O  CN = 4. ev = 1        therefore,
                                     6 O surrounding each Mg with octahahedron coordination, 4 O sur-
                                      rounding each Si with tetrahedron coordination, and 3 Mg and 1 Si
                                      surrounding each O with tetrahedron coordination

                (CaSO₄):   S-O  CN = 4 (based on the anisodesmic nature--no rr calculation needed),
                                  Ca-O  CN = 8 since it is an isodesmic bond, the rr is borderline and 
                                   mineral formed at a low temperature, and 1 S and 2 Ca arround each O.
                                   S-O ev = 3/2, Ca-O ev = 1/4

               (CaWO₄):  Ca-O  CN = 8
                                  W-O  CN = 4 , and 1 W and 2 Ca around each O since Ca-O ev = 1/4 and 
                                  W-O  ev = 3/2

               ( PbMoO₄):  Pb-O  CN = 8 
                                    Mo-O CN = 4, and 1Mo and 2 Pb around each O since Pb-O ev = 1/4 and
                                    Mo-O ev = 3/2

         b.  Ti-O, Mg-O, Pb-O, Zn-O, Mn-O, Na-O, Ca-O are all isodesmic bonds
               C-O, S-O, N-O, W-O, Mo-O are all anisodesmic and oxyacid anions
               Si-O is mesodesmic

    3.  Fe⁺² cannot proxy for Si⁺⁴ in quartz, SiO₂       first of all Fe-O always forms a 6 CN with
         O and Si always a 4 CN with O     next, the difference in valence numbers would be too
         large since there must be additional substitution with Si to adhere to the electroneutrality
         rule--this condition would require too much energy and produce a mineral different than
         quartz

    4.  a. strong (probable)--similar CN with O however, calculated CN are not the same but under temp. 
             conditions will be the same; also valence and electronegativities are the same  
         b. weak (improbable)--since Ba⁺² is too large and would form a different CN with O
             even though charges are the same and electronegativities are similar
         c. strong (probable)--since CN with O  and valences are the same; alsoa stronger ionic bond
             would form 
         d. weak(improbable)--even though both would form the same CN with O and both have the
              same charge, the ionic bond formed would be much weaker
         e. strong (probable)--since both have same valences and form the same CN with O and both
             would form similar ionic bond strength 
         f. weak (improbable)--since the differences in charge would result in a very large amount of
            electroneutrality to correct for; the CN with O are different and a much weaker ionic bond 
            would form considering electronegativities 
         g. strong-moderate  even though the charges are different by one as happens with Na⁺¹
             and Ca⁺² proxying in plagioclase, Al+3 and Si+4 could substitute to keep electronegativity
             of mineral; the CN with O would be the same and the electronegativities are quite similar
         h. weak(improbable)--since the CN with O would be different although valence is the same
             and electronegativities are similar
         i.  weak(improbable)--since CN with O would be different even though a stronger ionic bond
             would form and the valences are the same
         j. weak(improbable)--since a much weaker ionic bond would form even though both would 
            form the same CN with O and both have the same valence  

     5.  anisodesmic bonds form oxyacid anions and mesodesmic bonds form polymerization in minerals