Download Mineral Properties - Gordon State College

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Chapter 20:
ROCKS AND MINERALS
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley
This lecture will help you
understand:
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The Geosphere is Made Up of Rocks and Minerals
Minerals
Mineral Properties
Classification of Rock-Forming Minerals
The Formation of Minerals and Rock
Rock Types
Igneous Rocks
Sedimentary Rocks
Metamorphic Rocks
The Rock Cycle
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The Geosphere is Made Up of
Rocks and Minerals
• Just eight elements account for 98% of
Earth’s mass.
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The Geosphere is Made Up of
Rocks and Minerals
• From Earth’s early molten (or nearly molten) state
under the influence of gravity, the heaviest elements
sank to the center of the Earth. So the core is
composed of dense, iron-rich material.
• Lighter elements migrated toward Earth’s surface. So
the mantle is less dense than the core.
• The crust is composed of even lighter, silicon- and
oxygen-rich material.
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The Geosphere is Made Up of
Rocks and Minerals
Oxygen and silicon make up 75% of
Earth’s crust.
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Minerals
• They are naturally occurring (formed naturally
rather than manufactured).
• They are crystalline solids.
• They have an orderly and repeating
arrangement of atoms, ions, and or
molecules.
• They have a definite chemical composition,
with slight variations.
• They are generally inorganic.
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Minerals
Minerals are classified by:
• Chemical composition
• Crystal structure
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Minerals
Crystallization is the formation and growth of a
solid from a liquid or gas
— Atoms come together in specific chemical
compositions and geometric arrangements.
— The combination of chemical composition and
arrangement of atoms in an internal structure
makes each mineral unique.
— Many minerals are identifiable by their crystal
form.
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Minerals
• Some minerals can have the same
composition but have a different crystal
structure.
— Different arrangements of the same atoms result in different
minerals.
• Diamond and graphite are two examples
— Such minerals are called polymorphs.
— With a different crystal structure, the minerals will have
different properties.
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Mineral Properties
• Physical properties are an expression of
chemical composition and internal
crystal structure:
—Crystal form
—Hardness
—Cleavage and fracture
—Color
—Density
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Mineral Properties: Crystal Form
Crystal form—crystal shape—is the outward
expression of a mineral’s internal
arrangement of atoms.
• Internal atomic arrangement is determined by
atom/ion charge, size, and packing.
• The conditions in which the crystal grows also
affect crystal form.
—Temperature, pressure, space for growth
• Well-formed minerals are rare in nature—most
minerals grow in cramped confined spaces.
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Mineral Properties: Hardness
Hardness is the resistance of a mineral to
scratching.
• Hardness is dependent on the strength of a
mineral’s chemical bonds.
• Bond strength is determined by ionic charge,
atom (or ion) size, and packing.
• The Mohs Scale compares the hardness of
different minerals.
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Mineral Properties: Hardness
CHECK YOUR NEIGHBOR
Gold is a soft mineral because:
A.
B.
C.
D.
Its atoms are very tightly packed.
Its atoms are large.
Its atoms are tightly bonded.
It has a very high melting point.
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Mineral Properties: Hardness
CHECK YOUR ANSWER
Gold is a soft mineral because:
A.
B.
C.
D.
Its atoms are very tightly packed.
Its atoms are large.
Its atoms are tightly bonded.
It has a very high melting point.
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Mineral Propteries: Cleavage and
Fracture
Cleavage is the property of a mineral to break
along planes of weakness.
• Planes of weakness are determined by
crystal structure and bond strength.
Fracture occurs in minerals where bond
strength is generally the same in all
directions.
• Minerals that fracture do not exhibit cleavage.
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Mineral Properties: Color
• Color is an obvious feature for many
minerals, but it is not reliable for mineral
identification.
—Chemical impurities can change a
mineral’s color.
—A mineral may occur in many color
variations or be colorless.
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Mineral Properties: Density
Density is the ratio of a mineral’s mass to
its volume.
In simple terms, it is how heavy a mineral
feels for its size (volume).
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Mineral Properties
CHECK YOUR NEIGHBOR
Physical properties of a mineral are predominantly related
to
A.
B.
C.
D.
the external conditions of temperature, pressure, and amount
of space available for growth.
the chemical composition and the internal arrangement of the
atoms that make up the mineral.
crystal form, hardness, cleavage and fracture, and density.
all of the above.
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Mineral Properties
CHECK YOUR ANSWER
Physical properties of a mineral are predominantly related
to
A.
B.
C.
D.
the external conditions of temperature, pressure, and amount
of space available for growth.
the chemical composition and the internal arrangement of
the atoms that make up the mineral.
crystal form, hardness, cleavage and fracture, and density.
all of the above
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Mineral Properties
CHECK YOUR NEIGHBOR
The color of a mineral is predominantly related to
A.
B.
C.
D.
its chemical composition.
its internal arrangement of atoms.
its luster.
temperature and pressure conditions at the time of
crystallization.
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Mineral Properties
CHECK YOUR ANSWER
The color of a mineral is predominantly related to
A.
B.
C.
D.
its chemical composition.
its internal arrangement of atoms.
its luster.
temperature and pressure conditions at the time of
crystallization.
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Classification of Rock-Forming
Minerals
There are two classifications of minerals:
—Silicate minerals
—Nonsilicate minerals
Silicate minerals make up more than
90% of the Earth’s crust.
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Classification of Rock-Forming
Minerals
Silicate minerals are made up of silicon
(Si) and oxygen (O) atoms, along with
other elements (Al, Mg, Fe, Mn, and Ti).
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Classification of Rock-Forming
Minerals
The Silicates are divided into two groups:
• Ferromagnesian silicates
— Contain iron and/or magnesium
— Tend to have high density and are darkly
colored
• Nonferromagnesian silicates
— No iron or magnesium
— Tend to have low density and are light in
color
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Classification of Rock-Forming
Minerals
All silicate minerals have the same
fundamental structure of atoms—the
silicate tetrahedron.
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Classification of Rock-Forming
Minerals
Nonsilicate minerals make up about 8% of
Earth’s crust.
• Carbonate minerals
• Calcite, dolomite
• Oxide minerals
• Ore minerals—hematite, magnetite, chromite
• Sulfide minerals
• Ore minerals—pyrite, galena
• Sulfate minerals
• Gypsum, anhydrate
• Native elements
• Gold, platinum, iron
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Classification of Rock-Forming Minerals
CHECK YOUR NEIGHBOR
The silicates are the most common and abundant mineral
group, because silicon and oxygen are
A.
B.
C.
D.
the hardest elements on Earth’s surface.
the two most abundant elements in the Earth’s crust.
found in the mineral quartz.
formed in a tetrahedral structure.
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Classification of Rock-Forming Minerals
CHECK YOUR ANSWER
The silicates are the most common and abundant mineral
group, because silicon and oxygen are
A.
B.
C.
D.
the hardest elements on Earth’s surface.
the two most abundant elements in the Earth’s crust.
found in the mineral quartz.
formed in a tetrahedral structure.
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The Formation of Minerals and
Rock
Minerals form by the process of
crystallization.
Minerals crystallize from two primary
sources:
—Magma (molten rock)
—Water solutions
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The Formation of Minerals and
Rock
Minerals crystallize systematically based on
their respective melting points.
—The first minerals to crystallize from a magma are
those with the highest melting point and the lowest
amount of silica.
—The last minerals to crystallize from a magma are
those with lower melting points and higher
amounts of silica.
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The Formation of Minerals and Rock
Water solutions associated with later
stages of crystallization from magma
account for many important ore
deposits.
• As water solutions become chemically
saturated, minerals precipitate.
• Ore deposits can be deposited into
cracks or into the matrix of the rock
itself.
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The Formation of Minerals and Rock
• Water solutions can precipitate
chemical sediments such as carbonates
and evaporites.
• For chemical sediments, solubility rather
than melting point determines which
minerals will form first.
—Low-solubility minerals precipitate first.
—High-solubility minerals precipitate last.
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The Formation of Minerals and Rock
CHECK YOUR NEIGHBOR
In the crystallization of chemical sediments from a water
solution, low-solubility minerals precipitate first, because
A.
B.
C.
D.
they dissolve more easily.
they are more susceptible to being dissolved.
they are not easily dissolved.
they are infinitely soluble.
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The Formation of Minerals and Rock
CHECK YOUR ANSWER
In the crystallization of chemical sediments from a water
solution, low-solubility minerals precipitate first, because
A.
B.
C.
D.
they dissolve more easily.
they are more susceptible to being dissolved.
they are not easily dissolved.
they are infinitely soluble.
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Rock Types
A rock is an aggregate of minerals—a physical
mixture. The three categories of rock reflect how
they were formed:
• Igneous
• Formed from cooling and crystallization of magma or lava
• Sedimentary
• Formed from preexisting rocks subjected to weathering and
erosion
• Metamorphic
• Formed from preexisting rock transformed by heat, pressure,
or chemical fluids
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Igneous Rocks
• Igneous rocks are formed from the
cooling and crystallization of magma or
lava.
— Magma is molten rock that forms inside
Earth.
— Lava is molten rock (magma) erupted at
Earth’s surface.
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Igneous Rocks: Generation of
Magma
• Role of heat:
— Temperature increases within Earth’s upper
crust—the geothermal gradient—at an average
rate of 30°C per kilometer.
— Rocks in the lower crust and upper mantle are
near their melting points.
— Any additional heat (from rocks descending into
the mantle or rising heat from the mantle) may
help to induce melting.
— Heat is a minor player.
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Igneous Rocks: Generation of
Magma
• Role of pressure:
— Reduced pressure lowers the melting
temperature of rock.
— When confining pressures drop,
decompression melting occurs.
• Analogies and examples:
—The solid inner core
—A pressure cooker
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Igneous Rocks: Generation of
Magma
• Role of fluids
—Fluids (primarily water) cause rocks to melt
at lower temperatures.
—Analogy: salt added to water causes ice to
melt at a lower temperature.
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Igneous Rocks
CHECK YOUR NEIGHBOR
Even though the temperature at depth is hotter than rock’s
melting point, the rocks at depth are solid, because
A.
B.
C.
D.
they are under enormous pressure from rock above.
increased pressure prevents their melting.
temperature would have to be even higher to counteract the
increase in pressure.
all of the above.
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Igneous Rocks
CHECK YOUR ANSWER
Even though the temperature at depth is hotter than rock’s
melting point, the rocks at depth are solid, because
A.
B.
C.
D.
they are under enormous pressure from rock above.
increased pressure prevents their melting.
temperature would have to be even higher to counteract the
increase in pressure.
all of the above.
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Igneous Rocks
The mineral makeup of igneous rock is
dependent on the chemical composition
of the magma from which it crystallizes.
Three types of magma:
– Basaltic
– Andesitic
– Granitic
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Igneous Rocks
• Melting of rock into magma occurs over
a broad temperature range.
– Partial melting rules.
• Minerals with low melting points (high silica
content) are the first to melt.
• Partial melting results in a silica-enriched
magma.
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Igneous Rocks
Minerals crystallize systematically based on
their respective melting points.
• Minerals with high melting points(low silica content) are
the first to crystallize.
• The process of crystallization acts to enrich the
remaining magma with silica.
– Minerals with low melting points (high silica content) are
left in the melt.
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Igneous Rocks
Igneous rocks are classified according to
where they are formed.
• Rocks formed from magma that
crystallizes at depth are termed intrusive,
or plutonic rocks.
• Rocks formed from lava at the surface
are classified as extrusive, or volcanic
rocks.
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Igneous Rocks
There are three types of
volcanoes:
• Shield
• Cinder cone
• Composite
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Igneous Rocks
Igneous rock that cools below Earth’s
surface is called plutonic.
Granite is the most common plutonic rock.
Batholiths are large expanses of plutonic
rock.
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Sedimentary Rocks
Sedimentary rocks are products of 4
processes:
•
•
•
•
Weathering
Erosion
Deposition
Sedimentation
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Sedimentary Rocks
• Weathering—the physical breakdown
and chemical alteration of rock at
Earth’s surface.
• Two types of weathering:
— Mechanical weathering—breaking and
disintegration of rocks into smaller pieces.
— Chemical weathering—chemical
decomposition and transformation of rock
into one or more new compounds.
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Sedimentary Rocks:
Mechanical Weathering
• Frost wedging—alternate freezing and
thawing of water in fractures and cracks
promotes the disintegration of rocks.
• Thermal expansion—alternate expansion and
contraction due to heating and cooling.
• Biological activity—disintegration resulting
from plants and animals.
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Sedimentary Rocks:
Chemical Weathering
• Main producer of sediment.
• Breaks down rock components and the
internal structures of
• minerals.
• Most important
• agent is water.
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Sedimentary Rocks:
Erosion
• Erosion—the physical removal of
material by mobile agents such as
water, wind, ice, or gravity.
• Erosion does not occur in place. It
involves movement.
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Sedimentary Rocks:
Deposition
Deposition — the stage in
which eroded particles
come to rest. Larger
particles are the first to be
deposited. Smaller
particles are able to remain
with the flow. In this way,
sediments are sorted
according to size as they
are deposited.
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Sedimentary Rocks:
Sedimentation
• During sedimentation, sediment
particles are deposited horizontally layer
by layer.
• As deposited sediment accumulates, it
changes into sedimentary rock.
• Lithification occurs in two steps:
—Compaction
—Cementation
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Sedimentary Rocks:
Sedimentation
• Compaction—Weight of overlying
material presses down upon deeper
layers.
• Cementation—Compaction releases
“pore water” rich in dissolved minerals.
This mineralized “pore water” acts as a
glue to cement sediment particles
together.
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Sedimentary Rocks:
Classifying Sedimentary Rocks
• Sedimentary rock types are based on
the source of the material:
— Clastic rocks—transported sediment
particles—bits and pieces of weathered
rock (shale, sandstone, conglomerate)
— Chemical rocks—sediments that were
once in solution (travertine, halite,
limestone)
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Clastic Sedimentary Rocks
classified by particle size
Shale
• Mud-sized particles in thin layers
• Most common sedimentary rock
Sandstone
• Composed of sand-sized particles
• Quartz is the predominant mineral
Conglomerates
• Composed of particles greater than 2 mm in
diameter
• Consists largely of rounded gravels
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Chemical Sedimentary Rocks
Limestone:
— Most abundant
chemical rock.
— Composed chiefly of
the mineral calcite.
— Marine biochemical
limestones form as
coral reefs, coquina
(broken shells), and
chalk (microscopic
organisms).
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Chemical Sedimentary Rocks
Evaporites:
—Evaporation triggers the deposition of
chemical precipitates.
—Examples include rock salt and rock
gypsum.
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Chemical Sedimentary Rocks
Coal:
• Different from other rocks, because it is
composed of organic material.
• Stages in coal formation (in order):
—Plant material
—Peat
—Lignite
—Bituminous coal
—Anthracite coal
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Sedimentary Rocks
CHECK YOUR NEIGHBOR
The most characteristic feature of sedimentary rocks is
A.
B.
C.
D.
they contain fossils.
the lithification and cementation of sediments.
the layered sequence of strata.
the fusing of unconsolidated sediments into solid rock.
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Sedimentary Rocks
CHECK YOUR ANSWER
The most characteristic feature of sedimentary rocks is
A.
B.
C.
D.
they contain fossils.
the lithification and cementation of sediments.
the layered sequence of strata.
the fusing of unconsolidated sediments into solid rock.
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Metamorphic Rocks
• Metamorphic rocks are produced from:
—Igneous rocks
—Sedimentary rocks
—Other metamorphic rocks
• Metamorphism occurs via
recrystallization and mechanical
deformation.
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Metamorphic Rocks
Contact metamorphism:
• a body of rock is intruded
by magma
• is typically associated
with high temperatures
and high water content—
lots of chemical activity,
not much, or no,
mechanical deformation.
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Metamorphic Rocks
Regional metamorphism:
• the alteration of rock by both heat and
pressure over an entire region rather
than just near a contact between rock
bodies.
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Metamorphic Rocks
Metamorphic rock is defined by appearance
and mineral content:
• Foliated—layered in sheets (schist, slate, gneiss)
• Nonfoliated—not layered (marble and quartzite)
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Metamorphic Rocks
CHECK YOUR NEIGHBOR
Marble is an example of:
A.
B.
C.
D.
Crystalline, metamorphosed limestone.
Foliated metamorphic rock.
Recrystallized sandstone.
Nonfoliated mica.
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Metamorphic Rocks
CHECK YOUR ANSWER
Marble is an example of:
A.
B.
C.
D.
Crystalline, metamorphosed limestone.
Foliated metamorphic rock.
Recrystallized sandstone.
Nonfoliated mica.
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The Rock Cycle
Molten rock rises from the depths of
Earth, cools, solidifies, and eventually
returns to become magma again.
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