Powerpoint Presentation Physical Geology, 10e

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Atoms, Elements, and MineralsPhysical Geology
11/e, Chapter 2
Steve Kadel, Glendale Community College
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Minerals
A mineral is a . Consistent and
recognizable physical and chemical properties
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Atoms and Elements
An element An atom Composed of 3 types of
subatomic particles 1 2 3 A molecule
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Figure 2.4
The combining and conecting of atoms creates a
compound
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Atomic Structure
Protons and neutrons form the nucleus of an
atom Electrons orbit the nucleus in discrete
shells or energy levels
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Chemical Bonding
Chemical bonding Elements will typically be
reactive unless their valence shell is
full. Ions Positive and negative ions are
attracted to one another by.
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These two Clorine atoms have seven electrons in
their outer shells, so they need one more. They
can share their bonds to make them stronger.
Thus covalent bonding.
Sodium has an extra electron in outer shell so it
gives up to Chlorine. Clorine needs one due to
only having seven so it takes Na electron into
outer shell. Ionic bonding http//ithacasciencezo
ne.com/chemzone/lessons/03bonding/mleebonding/ioni
c_bonds.htm
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Chemical Bonding
Ionic bonding Covalent bonding Metallic
bonding
Ionic bonding of NaCl (sodium chloride)
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Helium has two electrons and fills the inner shell
Everytime we add a proton, electron, or neutron,
we change the atom, and if we change the atom, we
change the element.
The far right column has eight electron to fill
outer shell thus they are inert.
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Isotopes
Atoms of an element with different numbers of
neutrons are called isotopes Isotopes may be
either stable or unstable Stable isotopes
can be used to track climate change over time
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Composition of Earths Crust
Common elements Common mineral types Minerals
have crystalline structures Regular 3-D
arrangement of atoms
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Notice the two most common elements Oxygen and
Silicon
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Silicate Structures
The Silicon-Oxygen tetrahedron Strongly bonded
silicate ion Basic structure for silicate
minerals Sharing of O atoms in tetrahedra The
more shared O atoms per tetrahedron, the more
complex the silicate structure Isolated
tetrahedra (none shared) Chain silicates (2
shared) Double-chain silicates (alternating 2 and
3 shared) Sheet silicates (3 shared) Framework
silicates (4 shared)
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Non-silicate Minerals
Carbonates Contain CO3 in their structures (e.g.,
calcite - CaCO3) Sulfates Contain SO4 in their
structures (e.g., gypsum - CaSO4.
2H2O) Sulfides Contain S (but no O) in their
structures (e.g., pyrite - FeS2) Oxides Contain
O, but not bonded to Si, C or S (e.g., hematite -
Fe2O3) Native elements Composed entirely of one
element (e.g., diamond - C gold - Au)
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Minerals
A mineral must meet the following
criteria Crystalline solid Atoms are arranged in
a consistent and orderly geometric
pattern Rock-forming minerals Although over
4000 minerals have been identified, only a few
hundred are common enough to be generally
important to geology (rock-forming minerals)
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The structure of a mineral can be changed as in a
diamond or graphite. Both are made of pure
carbon, one is in sheets(graphite) and other is
in a three dimensional structure(diamond).
Chemically the same, but structurally theyre
different minerals. http//www.avogadro.co.uk/stru
cture/chemstruc/network/g-molecular.htm
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Minerals
Ore minerals Minerals of commercial
value Gemstones Prized for their beauty
and (often) hardness
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Mineral Properties

• Physical and chemical properties of minerals
  are closely
• linked to their atomic structures and
  compositions

Color Streak Luster Hardness Crystal form
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Mineral Properties
Cleavage
Fracture Specific gravity Magnetism Chem
ical reaction
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• The color of a mineral is one of its most obvious
  attributes, and is one of the properties that is
  always given in any description. Color results
  from a minerals chemical composition, impurities
  that may be present, and flaws or damage in the
  internal structure. Unfortunately, even though
  color is the easiest physical property to
  determine, it is not the most useful in helping
  to characterize a particular mineral.

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• The color of a mineral when it is powdered is
  called the streak of the mineral. Crushing and
  powdering a mineral eliminates some of the
  effects of impurities and structural problems,
  and is a better diagnostic for some minerals than
  their color. Streak can be determined for any
  mineral by crushing it with a hammer, but it is
  more commonly (and less destructively) obtained
  by rubbing the mineral across the surface of a
  hard, unglazed porcelain material called a streak
  plate.
• The color of the powder left behind on the
  streak plate is the mineral's streak. The streak
  and color of some minerals are the same. For
  others, the streak may be quite different from
  the color, as for example the red-brown streak of
  hematite, often a gray to silver-gray mineral.
  Using luster, color, and streak may be enough to
  permit identification of the mineral.

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• The luster of a mineral is the way its surface
  reflects light. Most terms used to describe
  luster are self-explanatory metallic, earthy,
  waxy, greasy, vitreous (glassy), adamantine (or
  brilliant, as in a faceted diamond). It will be
  necessary, at least at first, only to distinguish
  between minerals with a metallic luster and those
  with one of the non-metallic lusters.
• A metallic luster is a shiny, opaque appearance
  similar to a bright chrome bumper on an
  automobile.
• Other shiny, but somewhat translucent or
  transparent lusters (glassy, adamantine), along
  with dull, earthy, waxy, and resinous lusters,
  are grouped as non-metallic.

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• In some minerals, bonds between layers of atoms
  aligned in certain directions are weaker than
  bonds between different layers. Breakage will
  occur along smooth, flat surfaces parallel to
  zones of weakness. In some minerals, a single
  direction of weakness exists, but in others, two,
  three, four, or as many as six may be present.
• It may be difficult for the beginner to
  distinguish between cleavage and crystal faces.
  After all, both are smooth, planar surfaces. Two
  hints will help make the distinction easy.
• (1) If a mineral's outer surface shows tarnish,
  the crystal faces will be tarnished or dull if
  cleavage planes are present, they may be recently
  made and will be fresher and less altered.
• (2) If many surfaces are present parallel to one
  another, they are most likely cleavage surfaces.

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• The Mohs Hardness Scale is a relative scale. This
  means that a mineral will scratch any substance
  lower on the scale and will be scratched by any
  substance with a higher number. Diamond is not 10
  times harder than talc or 1.1 times harder than
  corundum, as would be the case with an absolute
  hardness scale. Most often we are able only to
  narrow down hardness to within a certain range
  for example, if an unknown mineral scratches a
  copper penny but does not scratch a glass plate,
  its hardness must be greater than 3.0 and less
  than 5.5. Usually this range of values is
  sufficient to identify an unknown.

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• When minerals form in environments where they can
  grow without interference from neighboring
  grains, they commonly develop into regular
  geometric shapes, or crystals, bounded by smooth
  crystal faces. The crystal form for a given
  mineral is governed by the mineral's internal
  structure, and may be distinctive enough to help
  identify the mineral. For example, quartz forms
  elongated, six-sided prisms capped with
  pyramid-like faces galena and halite occur as
  cubes and garnets develop 12- or 24-sided
  equidimensional forms. Interference from other
  mineral grains during growth may prevent
  formation of well-formed crystals. The result is
  shapeless masses or specimens that developed only
  a few smooth crystal faces. This type of specimen
  is much more common than well-formed crystals.

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• The specific gravity of a substance is a
  comparison of its density to that of water. To
  compare the specific gravity of any two minerals,
  simply hold a sample of one in your hand and
  "heft it," i.e., get a feeling for its weight.
  Then heft a sample of the other that is
  approximately the same size. If there is a great
  difference in specific gravity, you will detect
  it easily.

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• Magnetism - A few minerals are attracted to a
  magnet or are themselves capable of acting as
  magnets (the most common magnetic mineral is
  magnetite).
• Feel - Some minerals, talc and graphite, feel
  greasy when you rub your fingers over them. The
  greasiness occurs because bonds are so weak in
  one direction that your finger pressure alone is
  enough to break them and to slide planes of atoms
  past neighboring atomic layers.
• Taste - Taste is one of the last tests to be
  conducted, due to some minerals being poisonous.
  Some minerals taste salty-most notably halite
  (salt). Sylvite, which is similar to other halite
  properties, is bitter. NEVER TASTE A MINERAL
  UNLESS INSTRUCTED TO!
• Reaction with Dilute Hydrochloric Acid - This is
  a chemical property rather than a physical
  attribute. Carbon dioxide is released from the
  mineral and bubbles out through the acid,
  creating the fizz. Some minerals such as
  Dolomite will react only in a powder form.

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Igneous Rocks, Intrusive Activity, and the Origin
of Igneous RocksPhysical Geology 11/e, Chapter 3
Steve Kadel, Glendale Community College
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Rock
An aggregate of one or more minerals
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The Rock Cycle

• A rock is a
• The rock cycle shows
• Representation of how rocks are formed, broken
  down, and processed in response to changing
  conditions
• Processes may involve interactions of geosphere
  with hydrosphere, atmosphere and/or biosphere

Rock that is weathered and not transported is
called soil
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The Rock Cycle and Plate Tectonics

• Magma is created by melting of rock
• above a subduction zone
• Less dense magma rises and cools
• to form igneous rock
• Igneous rock exposed at surface
• gets weathered into sediment
• Sediments transported to low areas,
• buried and hardened into sedimentary rock
• Sedimentary rock heated and squeezed at depth to
  form metamorphic rock
• Metamorphic rock may heat up and melt at depth to
  form magma

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Igneous Rocks

• Magma
• Igneous rocks form when
• Intrusive igneous rocks form when magma
• Extrusive igneous rocks form
• http//www.pitt.edu/cejones/GeoImages/2IgneousRoc
  ks.html

Granite
Basalt
Notice the grain size of intrusive and extrusive
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Igneous Rock Textures

• Texture refers to the size, shape and arrangement
  of grains or other constituents within a rock
• Texture of igneous rocks is primarily controlled
  by cooling rate
• Extrusive igneous rocks cool quickly at or near
  Earths surface and are typically fine-grained
  (most crystals lt1 mm)
• Intrusive igneous rocks cool slowly deep beneath
  Earths surface and are typically coarse-grained
  (most crystals gt1 mm)

Fine-grained igneous rock
Coarse-grained igneous rock
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Igneous Rock Identification

• Igneous rock names are based on texture (grain
  size) and mineralogic composition

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Table 3.2
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Special Igneous Textures

• A pegmatite
• A glassy texture
• A porphyritic texture

Pegmatitic igneous rock
Porphyritic igneous rock
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Igneous Rock Identification

• Igneous rock names are based on texture (grain
  size) and mineralogic composition
• Textural classification
• Plutonic rocks (gabbro-diorite-granite)
• Volcanic rocks (basalt-andesite-rhyolite)
• Compositional classification
• Mafic rocks (gabbro-basalt)
• Intermediate rocks (diorite-andesite)
• Felsic rocks (granite-rhyolite)

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Igneous Rock Chemistry

• Rock chemistry, particularly silica (SiO2)
  content, determines mineral content and general
  color of igneous rocks
• Mafic rocks
• Felsic (silicic) rocks
• Intermediate rocks
• Ultramafic rocks have

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Intrusive Rock Bodies

• Intrusive rocks exist in bodies or structures
  that penetrate or cut through pre-existing
  country rock
• Intrusive bodies are given names based on their
  size, shape and relationship to country rock
• Shallow intrusions Dikes and sills
• Form lt2 km beneath Earths surface
• Chill and solidify fairly quickly in
  cool country
  rock
• Generally composed of
  
  fine-grained rocks

Insert new Fig. 3.11 here
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Intrusive Rock Bodies

• Intrusive rocks exist in bodies or structures
  that penetrate or cut through pre-existing
  country rock
• Intrusive bodies are given names based on their
  size, shape and relationship to country rock
• Deep intrusions

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Intrusive Rock Bodies

• Volcanic neck
• Dike
• Sill
• Pluton
• Large,
• Small plutons

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How Magma Forms

• Heat from below
• Heat vs. pressure

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How Magma Forms

• Hot water under pressure
• Mineral mixtures

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Magma Crystallization and Melting Sequence

• Minerals crystallize in a predictable order (and
  melt in the reverse order), over a large
  temperature range, as described by Bowens
  Reaction Series
• Discontinuous branch
• Continuous branch

Bowens Reaction Series
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Lessons from Bowens Reaction Series

• Large variety of igneous rocks is produced by
  large variety of magma compositions
• Mafic magmas will crystallize into basalt or
  gabbro if early-formed minerals are not removed
  from the magma
• Intermediate magmas will similarly crystallize
  into diorite or andesite if minerals are not
  removed
• Separation of early-formed ferromagnesian
  minerals from a magma body increases the silica
  content of the remaining magma
• Minerals melt in the reverse order of that in
  which they crystallize from a magma

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Magma Evolution

• A change in the composition of a magma body is
  known as magma evolution, due to Bowens reaction
  series.
• Magma evolution can occur by differentiation,
  partial melting, assimilation, or magma mixing
• Differentiation
• Partial melting

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Magma Evolution

• Assimilation
• Magma mixing

Insert new Fig. 3.22 here
Insert new Fig. 3.23 here
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Igneous Activity and Plate Tectonics

• Igneous activity occurs primarily at or near
  tectonic plate boundaries
• Mafic igneous rocks are commonly formed at
  divergent boundaries
• Intermediate igneous rocks are commonly formed at
  convergent boundaries

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Igneous Activity and Plate Tectonics

• Felsic igneous rocks are commonly formed adjacent
  to convergent boundaries
• Intraplate volcanism