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Lecture Outlines
Physical Geology, 14/e
Plummer, Carlson & Hammersley
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Atoms, Elements, and Minerals
Physical Geology 14/e, Chapter 2
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Minerals
Mineral – a naturally occurring,
inorganic, crystalline solid that has a
specific chemical composition.
• forms in the geosphere,
hydrosphere, biosphere, and even
the atmosphere
• consistent and recognizable
physical and chemical properties
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Atoms and elements
Element – a substance that cannot be
broken down to other substances by
ordinary chemical reactions
Atom – the smallest unit of a substance
that retains the properties of that element
• protons (+ charged)
• neutrons (0 net charge)
• electrons (- charged)
Molecule – the smallest unit of a
compound that retains the properties of
that substance
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Atomic structure
Protons and neutrons form the nucleus of an
atom
• represents tiny fraction of the volume at
the center of an atom, but nearly all of the
mass
Electrons orbit the nucleus in discrete shells
or energy levels
•
represent nearly all of the volume of an
atom, but only a tiny fraction of the mass
• electrons = protons
• chemical reactions involve only
outermost shell (valence) electrons
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isotopes
Isotopes – atoms of an element with different
numbers of neutrons
•
stable isotopes
o retain all of their protons and neutrons
through time
o stable isotopes of oxygen can be used to
track climate change over time
•
unstable or radioactive isotopes
o spontaneously lose proton(s) and/or
neutron(s) from their nuclei over time
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Chemical bonding
Chemical bonding – controlled
by outermost shell (valence) electrons
• elements will typically be reactive
unless their valence shell is full
Ions – atoms or groups of atoms with
unequal numbers of protons and
electrons, thus having a non-zero
charge
• positive and negative ions are
attracted to one another and may
stick or chemically bond together
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Chemical bonding
Ionic bonding – involves the
transfer of valence electrons from
one atom to another
Covalent bonding – involves
sharing of valence electrons among
adjacent atoms
Metallic bonding – electrons
flow freely throughout metals;
results in high electrical conductivity
Ionic bonding of NaCl (sodium chloride)
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Elements in the earth
Common elements
• ~ 97% of the atoms in the crust are
represented by 8 common elements: O, Si,
Al, Fe, Ca, Na, K, Mg
Common mineral types
• most minerals are silicates (Si + O)
Minerals have crystalline structures
• regular 3-D arrangement of atoms
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Silicate structures
Silicon-oxygen tetrahedra
• Strongly bonded silicate ion
• Basic structure for silicate
minerals
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Silicate structures
Sharing of O atoms in tetrahedra
• the more shared O atoms per
tetrahedra, the more complex the
silicate structure
o isolated tetrahedra (none shared)
o chain silicates (2 shared)
o double-chain silicates
(alternating 2 and 3 shared)
o sheet silicates (3 shared)
o framework silicates (4 shared)
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Non-Silicate minerals
Carbonates – contains CO3 in their structures (e.g., calcite - CaCO3)
Sulfates – contains SO4 in their structures (e.g., gypsum - CaSO4. 2H2O)
Sulfides – contains S (but no O) in their structures (e.g., pyrite - FeS2)
Oxides – contains O, but not bonded to Si, C or S (e.g., hematite - Fe2O3)
Native elements – composed entirely of one element (e.g., diamond – C)
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minerals
Mineral criteria
• crystalline solid, atoms are
arranged in a consistent and
orderly geometric pattern
• naturally occurring geological
processes
• specific chemical composition
with some variation
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minerals
Rock-forming minerals
• > 4500 minerals identified
• ~ 20 form the majority of all
rocks (rock-forming minerals)
• > 90% of Earth’s crust is
composed of minerals from only
5 groups (feldspars, pyroxenes,
amphiboles, micas, quartz)
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minerals
Ore minerals – minerals of
commercial value
• most are non-silicates (primary source
of metals)
• must be able to be extracted profitably
to be considered current resources
Gemstones
• prized for their beauty and (often)
hardness
• may be commercially useful
• diamond, corundum, garnet, and
quartz are used as abrasives
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Mineral properties
Color – visible hue of a mineral
Streak – color left behind when mineral is
scraped on unglazed porcelain
Luster – manner in which light reflects off
surface of a mineral
Hardness – scratch-resistance
Crystal form – external geometric form
Physical and chemical properties of minerals are closely
linked to their atomic structures and compositions
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Mineral properties
Cleavage – breakage along flat planes
Fracture – irregular breakage
Specific gravity – density relative to
that of water
Magnetism – attracted to magnet
Chemical reaction – calcite fizzes in
dilute HCl
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End of Chapter 2
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