MINERALS Chapter 3

 

A.                 Review of Chemistry (will NOT be on the Test)  pp. 54-58

1.      Structure of the atom Fig. 3.3, page 56

a.      Nucleus—protons, neutrons

b.      Electrons----orbitals, shells

2.   Definitions:   atomic number, atomic weight, element, isotope, ions (cations + & anions -) (see Fig 3.9, p. 62)

3.   Electrons and Orbitals

4.   Bonding:  ionic and covalent models

 

B.                 Introduction to Minerals NOTE: this section (B) does not parallel the textbook, so take additional notes if necessary

1.       Strict Definition:  4 criteria; A mineral must: p. 59 (note: slightly different in text----use the one below)

aBe naturally occurring

a.      Be inorganic

b.      Have a definite chemical composition (within defined limits)

c.       Have a definite crystal structure (be a crystalline solid)

2.            Minerals vs. Rocks

a.      Minerals normally consist of 1-5 major elements

b.      Rocks normally consist of 1-5 major minerals

c.       Minerals usually have a few “trace elements”---less than 5% of total

d.      Rocks usually have a few “accessory minerals”—less that 5% of total

e.      Minerals are HOMOGENEOUS, Rocks are NOT

3.            Definitions

a.      Solid State

i.        Crystallinity---crystals and the crystalline state

ii.      Two criteria for the crystalline state

1.      Regular geometric arrangement of atoms/ions (unit cell)

2.   Periodicity (systematic translational repeats in 3-D space)

iii.     Differences between molecules, crystalline solids and amorphous solids

iv.     Melting behavior of crystals and amorphous solids (glass)

v.      Growth of crystals:  “stacking of unit cells” vs. physical reality

1.      why some mineral grow with crystal faces and some don’t

b.      Solid Solution (why chemical composition varies “within defined limits”

4.            Nomenclature:

a.      Chemical Formula: every mineral has a distinct chemical formula

b.      Name:   almost every mineral has a distinct name:  Example:  quartz or calcite

 

C.                 Stability

1.  Definition: the energetically most favorable state for a given “system”

2.  Stable, Unstable, Metastable

3.  Example of diamond/graphite; Polymorphism (definition)

4.  Preview:  concept of stability applies to weathering, metamorphism, cooling of a magma; precipitation of minerals

 

D.                Physical Properties of Minerals   pp. 65-67  (note: the text goes into more detail than will be required for the test)

1.            All physical (and chemical) properties of a mineral “species” (quartz, for example) depends only on its: 

a.            Crystal Structure and

b.            Chemical Composition

2.            Because crystal structure and chemical composition are also what makes each mineral “species” unique, a mineral can be identified based on it unique SET of physical properties without having to determine its composition or structure.

3.            Physical Properties:  color, streak, luster, hardness, form (habit), cleavage, fracture, specific gravity (density)

 

E.                       Crustal Abundance of the Elements

1.            What is the crust?  Diagram showing crust, mantle, Moho

2.            The top 8 elements:  O, Si, Al, Fe, Ca, Na, K, Mg see Table 3.2, p. 63

For the test, you should know that:

a.            Oxygen is the only anion in the top 8

b.            Oxygen accounts for about 50% of the weight of the crust

c.             Silicon and oxygen together account for about 75% of the weight of the crust

d.            These top 8 elements account for about 98.5% (almost 99%) of the weight of the crust

e.            The other 90 or so elements account for only about 1.5% of the weight of the crust

f.              Be able to recognize the 8 elements in this list (but you don’t have to know them in any order)

3.            Abundances of minerals:  about 3500, 350 and 35

a.            about 3500 total known minerals-----the list grows a bit each year

b.            about 350 “important minerals”----mostly economically important minerals

c.             about 35 rock-forming-minerals—RFM--  these are minerals that are sufficiently abundant in nature as to be common, major constituents of rock-------The crustal abundance of the elements is such that only a relative few minerals qualify as RFM

 

F.                                          Classification of Minerals  See Table 3.3, p.63, but also know the table below (E-2) for the test

1.      General: Unlike plants and animals (whose numbers dwarf those of minerals) there is no rigid, complex taxonomic hierarchy for classifying minerals

a.            Minerals are divided into classes based on chemical composition

b.            Each class is divided into subclasses

c.             Some are combined in  “groups” = “families” and treated as minerals (example:  olivine, feldspar, pyroxene, etc)

d.            Some are true individual mineral “species” (examples:  quartz, calcite, diamond, etc.)

e.            Some minerals have “varieties” (example:  amethyst is a var. of quartz; emerald is a gem variety of beryl)

2.            Examples of a few minerals and their respective classes (know for test)

CLASS                        CRITERION                                     EXAMPLE

                                    Native element           not a compound                                  diamond, graphite, native gold

                                    Carbonate                   contains (CO3) groups                        calcite, dolomite

                                    Sulfate                        contains (SO4) groups                        gypsum

                                    Sulfide             contains S, but not O                pyrite

                                    Silicates                      contains (SiO4) groups                       many examples

3.            Silicates:  most of the earth’s crust consists of silicates; therefore they will be considered in greater detail

a.            The basic building blocks of silicates are the SiO4 groups that have shape of a tetrahedron see page 63, Fig 3.10

b.            Silicates are classified by the extent (or degree) to which individual tetrahedral are linked directly to other tetrahedra  (direct links are formed by sharing a common oxygen (= each sharing a “corner” with the other)

4.             Subclasses of Silicates with examples   see p 63-65 and the Fig 3.11, p. 64

SUBCLASS                IDEAL T:O ratio       EXAMPLE

Isolated Tetrahedron   1:4                 olivine (garnet)

Single Chain               1:3                      pyroxene

Double Chain             4:11                  amphibole

Sheet                           2:5                     micas (biotite, muscovite), clays

Framework                 1:2                     quartz, feldspars