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UNIT 2: Earth Materials
Overview of the Unit
Minerals:
-definition
-formation
-types
-identification/tests
Rocks:
-definition
-formation and rock
cycle
-categories/types
-identification
Materials as a resource
-mining (oral
presentation)
First… a review of basic chemistry
• Atoms are composed of a dense nucleus containing
protons and neutrons that is orbited by electrons. The
number of protons indicates what element it is.
• These electrons orbit in distinct energy levels (shells).
Each shell can only have a specific number of electrons
before it becomes full and a new shell must be started.
The electrons in the outermost shell are called valence
electrons.
• The number of valence electrons dictate how the
elements react. Remember: atoms want full valence
shells, either by gaining or losing electrons (ionic bonds),
or by sharing electrons (covalent bonds).
A closer look at ionic bonds
• When a metal and a non-metal bond, the metal will
transfer 1 or more electrons to the non-metal so that they
both have full valence shells.
• The result is that the positive metal ion is attracted not
only to the negative non-metal ion it gave its electron(s)
to, but also all the other non-metal ions.
• This results in a crystal lattice structure.
More on crystals...
Not all crystals take this shape.
(Only ionic compounds in a
1-1 ratio like NaCl)
Other ionic compounds not in
1-1 ratios (ie. BeCl2) may
have different structures.
Even some covalent bonds
result in the formation of
crystals (diamond, for
example, which is just a
carbon crystal).
Properties of Crystals
• The bonds between ions in
the same plane are quite
strong, but the attraction
between planes may not
be.
• As a result, crystals
generally appear to have
very distinct shapes.
Minerals
• Definition: A mineral is a naturally
occurring, inorganic, solid element or
compound with definite composition and
regular internal crystal structure.
Classifying Minerals
• Surprisingly, using colour to classify or identify a
mineral is usually not appropriate.
• The reasons for this are
1) Many minerals may have the same colour for
different reasons
2) The same mineral may be found in several different
colours due to impurities inside the mineral.
Example: Pure corundum is colourless, and is often used
as grit in sandpaper. When colour is added we get...
Red --> rubies
Blue --> sapphire
Classifying Minerals
Minerals can be classified based on two properties...
1) composition
2) crystal structure
Here are some common groups…
Silicates:
• composed of silicon and oxygen and often other elements
• most common minerals (since Si and O are the two most
common elements in Earth’s crust)
• subdivided based on crystal structure (we won’t go into
details here)
• Some common examples:
– quartz (SiO2) --> used to make glass
» also found in some watches
» with a purple tint (impurities) it is called
amethyst
– feldspars --> also contain Al + either Na, K, or Ca
– ferromagnesians --> also contain Fe and/or Mg
– clays --> sheets of Si and O stacked on each other
» weak bonds between sheets, thus slippery
» may absorb water and expand
Quartz
Silicates
Amethyst
Clay - talc
(Mg, Si, O, OH)
Feldspar - nepheline
(Na, K, Al, Si, O)
Ferromagnesian - biotite
(K, Fe, Mg, Al, Si, O, OH, F)
Some Non-Silicates
Carbonates
Sulfates
• metals + CO3
• metals + SO4
• most common carbonate is • Example: gypsum
calcium carbonate
(calcium sulfate with
(CaCO3)
water, CaSO4(2H2O))
• Note: Calcite is a group in
the form of XCO3 where
X is an element in the
same group as Ca.
Some Non-Silicates
Sulfides
• metals + S (no O)
• Example: pyrite (fools
gold)
Oxides
• metals + O
• Examples:
– corundum (Al2O3)
– magnetite (Fe3O4)
– hematite (Fe2O3)
Some Non-Silicates
Hydroxides
• metals + OH
• Example: gibbsite
(Al(OH)3)
Halides
• metals + a halogen
• Example: halite (NaCl)
Native Elements
• any mineral consisting of a
single element
• Example: gold