EAS105- Final Exam Guide - Comprehensive Notes for the exam ( 96 pages long!)

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EAS105
Final EXAM
STUDY GUIDE
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MINERALS EAS 105 Dr. Clark
- Chapter 3, p. 60-85
The Changing Earth
7e
Definition:- Minerals are inorganic, naturally occurring solids. They are
crystalline substances with characteristic internal structure, and
chemical compositions that are either fixed, or vary within fixed limits.
a. inorganic therefore certain materials, as noted: vegetation, coal, oil
and gas, all of which are derived from strictly organic sources, are out;
however, many organisms secrete/metabolize shells and hard parts that
are identical to true minerals that can also be produced by inorganic
processes, and in this case then count as minerals
- NOTE “inorganic” does NOT mean “has no carbon”, even though Earth
has carbon-based life forms
b. naturally occurring synthetic compounds which conform to the
definition in every other respect don’t count
c. solids at atmospheric T&P; a peculiarity noted: thus water in the form
of ice counts as a mineral
d. crystalline structure defined: means that they have a consistent,
repeating internal arrangement of atoms; glass has no ordered
arrangement of atoms, and is amorphous (obsidian, volcanic class)
e. fixed or varies within fixed limits some minerals have fixed chemical
compositions (e.g. quartz, SiO2, and calcite, CaCO3), whereas others vary
due to ionic substitution (e.g. plagioclase feldspar, olivine)
1. The Nature of Minerals
- minerals are nothing more than chemical compounds that conform to the
above definition
- atoms, ions, ion groups and molecules are bonded to make stable
chemical compounds; there are several interparticle bond types; we will
highlight three of them
a. Ionic Bond
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- atoms of one element, called a cation, give up one or more electrons to
become positively charged (e.g. Na+, K+, Mg2+, Ca2+, Si4+); the electrons are
accepted by another element called an anion, to become negatively
charged (e.g. O2-, S2-)
- cations and anions are connected by a strong electrochemical bond; a
greater variety of minerals use ionic bonds than any other type
- both the cation and anion achieve a stable electron configuration, e.g. Na+
+ Cl- NaCl (halite or salt)
b. Covalent Bond
- described: electrons are shared between atoms (may be of same or
different element) to achieve a stable electron configuration
- in diamond, each C is single-bonded to 4 other C atoms, but in graphite, at
different P & T, each C is bonded to 3 other C atoms in alternating single
and double bonds [like benzene ring], to produce sheets, bonded to each
other by
c. van der Waal’s or Residual Bond
- electrical asymmetry of bonded atoms and molecules produces weak
residual or surface charges; characterized: these are weak bonds that are
easily broken
- different minerals, such as diamond and graphite, that have the same
chemical composition but different crystal structures, are called
something: polymorphs (many forms); they will have different physical
properties as a result
2. Crystals
- minerals are crystalline by virtue of a particular characteristic: their
ordered internal arrangement of atoms, and not by their external form
(which may be more pleasing, and being relatively less common, more
valuable)
- imperfections are due to such things as mutual interference, flaws
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