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, B_xO_y^-Z, Si_xO_y^-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)
               Sulfides, including Sulfarsenides, Arsenides, Sulfosalts ( main anion is S^-2)
               Oxides ( main anion is O^-2)
               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, B_xO_y^-Z)
               Phosphates ( the oxyacid anion, PO₄^-3)
               Sulfates ( the oxyacid anion, SO₄^-2)
               Tungstates ( the oxyacid anion, WO₄^-2)
               Silicates ( the oxyacid anion, Si_xO_y^-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:

    E.   Mineral Varieties

          1. based on chemical rich minerals
             -a mineral which can be appropriately expressed with an adjective denoting an
              unusually large amount of chemical constituent(s)--some examples of  modifers are:
                            aluminian = Al-rich      ferrian = Fe⁺³-rich
                            calcian = Ca-rich         magnesian = Mg-rich
                            chromian= Cr-rich       manganoan = Mn-rich
                            ferroan = Fe⁺²-rich
              -some specific mineral varieties would be manganoan aegerine, ferrian diopside or
               magnesian augite

          2. based on crystalline types
             -based on crystal size, color, or special appearance--many examples apply to quartz

               a. coarsely crystalline quartz
                     rock crystals--colorless;  amethyst--purple:  rose quartz--rose;  smoky quartz--
                       smoky yellow to brown to black;  citrine--light yellow;  milky quartz--milky
                       white; rutilated quartz--with inclusions of rutile

               b. microcrystalline quartz  
                    1. fibrous varieties:
                        chalcedony--waxy brown to gray often mammillary;  chrysoprase--apple green;
                        agate--parallel somewhat curved bands;  heliotrope (bloodstone)--green with
                        small red spots in it
                        
                    2. granular varieties:
                        flint or chert--flint is black with some chalk while chert is light colored;  jasper--
                                 red color caused by hematite

II.  Related Topics

     A.  Exsolution
          -is the association of similar composition minerals formed almost instantaneously from a
           cooling magma resulting in stringers of one mineral appearing in the other more abundant
           mineral--this can occur if the two minerals have cations close to ionic substitution at high
           temperature but not at the lower solidification point or temperature of formation of the
           minerals--examples are perthites and antiperthites (macro-, micro- and crypto-)
                        perthite is albite (Ab, NaAlSi₃O₈) stringers in orthoclase (Or, KAlSi₃O₈)
                        antiperthite is Or stringers in Ab

    B. Pseudomorphism
         -a form or shape displayed by "mineral A" in occurrence with "mineral B" in which
          the shape displayed by mineral A( not a normal form of A) is that of mineral B--ie. the existence  
         of a mineral with the outward form of another

                  kinds of pseudomorphism:
                        1. encrustation
                           -one mineral is deposited over crystals of another as quartz (hex.) encrusting
                             cubes of fluorite (iso.)--the more solublized fluorite can then be dissolved
                             leaving a cast of its form in the quartz
                      
                        2. alteration
                           -a mineral can be altered to produce an external or outer layer of another
                            which takes on the form of the altered mineral--examples are: the change of
                            anhydrite, CaSO₄ to gypsum, CaSO₄.H₂O;   the change of galena, PbS to
                            anglesite PbSO₄;  the oxidation or change of pyrite, FeS₂ or siderite, FeCO₃
                                      to limonite, FeO(OH).nH₂O

                        3. substitution
                           -a gradual removal of the original mineral and a molecule for molecule replace-
                            by another simultaneously--examples are: silica replacing fluorite; silica replac-
                            ing wood

     C.  Mineraloids
          -substances resembling minerals but are non crystalline since they have no ordered atomic
           arrangement--these mineral gels or glasses are not true minerals because they are amor-
           phous
          -these substances form under low temperature and low pressure conditions and commonly
           are products of chemical weathering processes--they often occur in mammillary, botry-
           oidal, or stalactitic masses as opal, and limonite

     D.  Metamict Structure
         -minerals whose original atomic structure has been altered by radiation from the decay
           of radioactive elements--the original ordered atomic arrangement may be reconstituted
           often by the exposure of heat by the altered arrangement 
         -the reconstitution process may result in emission of heat which can cause the mineral to ap-
           pear incandescent
         -a solid with a metamict structure may be considered a type of amorphous (mineraloid)
           substance
         -examples of metamict substances can occur with allanite and zircon