What class of mineral forms when the element c is bonded with element o, as in the mineral calcite?

Mineral classification is based primarily on the chemical composition, atomic
structure, degree of ionic substitution, and color and crystalline state of minerals

I. Mineral Classification

    A. Mineral Classes
         - minerals are classified primarily on the main anion ( O-2, S-2, etc.), anionic complex (oxyacid
          anion) (OH-1, SO4-2, CO3-3, PO4-3, BxOy-Z, SixOy-Z, etc), or lack of an anion(native elements)
         - some of the classes are listed below with the chemical characterisic used to classify them--find
            more mineral classes with the corresponding anion or complex anion in the text

Native elements ( comprised of atoms of only one element and no anion)----covalent by

                 nature--- atomic structure cannot be determined by Pauling’s Rule #1(radius ratio)
               Sulfides, including Sulfarsenides, Arsenides, Sulfosalts ( main anion is S-2)---covalent by
                 nature—atomic structure cannot be determined by Pauling’s Rule #1 (radius ratio)
               Oxides ( main anion is O-2)----almost all are comprised of isodesmic bonds--atomic
                  can be determined by Pauling’s Rule #1 (radius ratio)
               Hydroxides (main anion complex is OH-1)
               Halides ( main anion is a halogen as Cl-1, F-1, Br-1, I-1)
               Carbonates ( the oxyacid anion, CO3-3)
               Nitrates ( the oxyacid anion, NO3-1)
               Borates ( the oxyacid anion, BxOy-

Z)
               Phosphates ( the oxyacid anion, PO4-3)
               Sulfates ( the oxyacid anion, SO4-2)
               Tungstates ( the oxyacid anion, WO4-2)
               Silicates ( the oxyacid anion, SixOy-Z)

    B. Mineral Subclasses
        -some classes can be subdivided based on chemical or structural grounds--examples are
         the 1. Native Element Class which is divided into minerals with metallic bonding (metals),
         those with mostly covalent bonding ( nonmetals), and those with a mixture (semimetals);
         and the 2. the Silicate Class, with 6 subclasses (neso-, soro-, cyclo-, phylo-, tecto-silicates)
         based on the linkage of the silica tetrahedra--details concerning these subclasses will be
         treated later under a discussion of the non silicates and silicates

    C. Mineral Groups
        -classes or subclasses can be further divided based on atomic structure and similar chem-
         istry--examples are isomorphic (isostructural) groups, polymorphic groups and groups based
         on a general empirical formula with consistent properties

1. isomorphic group is a group of minerals with the same atomic structure but different chemical formulas--atoms of different elements representing equivalents in minerals

of this group have the same C.N.--FeCO3 (siderite) and CaCO3 (calcite) belong to

the same isomorphic group in the carbonate class because in both cases there are 6 O around each Fe and Ca respectively, 3 O around each C, and one C and 2 Fe or

Ca around each O--often the same atomic structure in different minerals reflects

similar chemical and physical properties and similar crystallography
- some examples of isomorphic (isostructural) groups are:

--in the oxide class-

                           hematite group, spinel group, rutile group
                    --in the carbonate class-
                           calcite group, aragonite group
                    --in the sulfate class-                            barite group

--in the silicate class-

                           (and nesosilcate subclass)--garnet group
                           (and inosilicate-pyroxenes subclass)--sodium pyroxene group
                           (and inosilcate-amphibole subclass)--sodium amphibole group

-isomorphism can exist with minerals which are not in the same mineral class--since they

               are not in the same mineral class they cannot be in the same isomorphic group--NaNO3
                    (nitratite) is isomorphic or isostructural with the minerals in the calcite group of the carbonate
            class including siderite and calcite

2. polymorphic group is a mineral group belonging to the same mineral class, all having the

same chemical formula but different atomic structures--these usually form or are stable

under different temperatures or pressures whereby the same cation forms a different

C.N. with the same anion--or the same CN exists but there is a different bond angle

between polyhedra--the difference in atomic structures result in polymorphs

often forming in different crystal systems

-some examples of polymorphs are:

a. calcite and aragonite--CaCO3---calcite is hexagonal and aragonite, orthorhombic

                    b. pyrite and marcasite--FeS2---pyrite forms at a high temperature and is isometric
                       while marcasite forms at a low temperature and is orthorhombic
                    c. quartz, tridymite, cristobalite, stishovite and coesite--SiO2---quartz forms at a
                        low temperature and forms in the hexagonal system, cristobalite forms at a high
                        temperature and forms in the tetragonal system, while tridymite is an intermediate
                        temperature form which is orthorhombic---coesite is stable at high pressures and
                        is associated with meteor impact and is a monoclinic mineral---stishovite is tet-
                        ragonal and is thought to be associated with rocks from Mars
                     d. kyanite and andalusite--Al2SiO5---kyanite is triclinic and is formed at a high
                         temperature and andalusite is orthorhombic and is the low temperature form
                     e. microcline, orthoclase, sanidine--KAlSi3O8---microcline, a triclinic mineral is
                         the low temperature variety, sanidine, a monoclinic mineral is the high temper-
                         ature variety and orthoclase is a monoclinic mineral which forms at an inter-                          temperature

kinds of polymorphism:
-two types of polymorphism are recognized according 1. to whether a change from

                    one polymorph to another is reversible and takes place at a definite temperature and
                    pressure, or 2. is irreversible and can change in only one direction at a certain temperature

                      1. enantiotropy
                           -a reversible change as:
                               quartz >< tridymite                                            or                                 graphite >< diamond

2. monotropy
-a one way change between polymorphs as:

marcasite > pyrite marcasite to pyrite but not vice versa (irreversible)

-also, polymorphs can also be categorized as to the nature of their change in respect to

the degree of reconstitution of the atomic structure

1. reconstructive change - is the breaking of atomic bonds and a reassembly of structural units--this type of

change involves alot of energy and the change is not readily reversed and is

sluggish

quartz > tridymite > cristobalite

2. displacive change
-atomic bonds are not broken and the original structure is maintained--there is

only a slight displacement of the atoms resulting in different bond angles--this change is instantaneous and involves little energy high quartz > low quartz

3. ordered-disordered change
-microcline (KAlSi3O8) has an ordered arrangement of the Si and Al in its

structure while the same for orthoclase is disordered--the disordered form

will have more symmetry since it forms at a higher temperature

          3. Other Groupings
              -minerals grouped based on the same general or empirical formula such as the pyroxene,
               amphibole and mica groups

D. Mineral Series
-classes and groups can be subdivided into mineral series in which solid solution is most prominently displayed

solid solution is a homogeneous crystalline mineral of variable composition comprised of

a mixture of end members in which there is ionic substitution between some cations of the end members--the principles of ionic substitution was treated earlier in the semester

-the type or quantity of cation(s) which can proxy for locations in the atomic structure

             of a mineral during mineral formation to a large degree is a function of temperature--in
             most cases examples of proxying cations in a mineral series are Ca+2 and Na+1,
             Al+3 and Si+4, and Fe+2 and Mg+2

-some examples of solid solution series are:

a. Plagioclase series (coupled ionic substitution)

-end members are CaAl2Si2O8 (anorthite) (An) and NaAlSi3O8 (albite) (Ab) in
which there is a proxying between both Na and Ca, and Al and Si--a table below expresses the different plagioclase minerals based on the degree of ionic sub-

stitution of Na and Ca, and Al and Si in end members: