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Geosphere Materials
Chapter 4
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You will learn
• Chemical Composition of the Geosphere
• What Minerals Are: How They Are Made
• Physical Properties of Minerals and Uses
• How Minerals Change
• How Rocks Form and Change
• Uses for Rocks
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Figure 4-2 Rocks are the most common geosphere materials, and can
be fun, dangerous, beautiful, and useful.
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The Geosphere’s Chemical
Composition
Elements
Minerals
Rocks
Atoms
Nucleus
Protons (+)
Neutrons (o)
Electrons (-)
Can’t be broken down into other substances
8 elements make up >98% of geosphere’s mass
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Composition of the Geosphere
Crust can be directly observed and sampled
Composition of deep Earth—estimated from:
• Density of Earth
• Density variations from seismic velocities
• Composition of meteorites
• Assumptions of formation of solar system
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Figure 4-4 Average Chemical Composition of the Geosphere Crust (a) The
chemical makeup of the geosphere as a whole. (b) Chemical makeup of oceanic
and continental crust.
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Differences between
Continental and Oceanic Crust
• The combined percentage of iron and magnesium
in oceanic crust (12.7%) is about 60% greater
than that in continental crust (8.0%).
• The percentage of calcium in oceanic crust (8.2%)
is nearly twice that in continental crust (4.6%).
• The percentage of potassium in continental crust
(1.5%) is 15 times that in oceanic crust (0.1%).
• The percentage of silicon in continental crust
(28.3%) is 20% greater than that in oceanic crust
(23.6%).
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Figure 4-5 Elements Bond Together by Transferring or Sharing Electrons
(a) Ionic bonding (transfer) (b) Covalent bonding (sharing).
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Common Rock-Forming Minerals in
Geosphere
• Quartz
• Feldspar
• Ferromagnesian minerals
Each is identified by a unique combination of physical and
chemical properties:
• Composition
• Color
• Luster
• Hardness
• Density (Specific Gravity)
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Graphite is
dark, soft,
flaky.
Diamond is very
hard and commonly
translucent
Figure 4-6 Diamond and Graphite Their internal structures explain why these
two minerals have different crystal forms and physical properties, even though
they’re both made solely of carbon.
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Quartz: the Silicon-Oxygen Mineral, SiO2
Si4+ + 4 O2- = SiO4 tetrahedron
small Si ion between 4 larger O ions
SiO4 tetrahedra can combine with
others to form chains, rings, sheets,
3D frameworks
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Quartz
SiO2
• Clear, white, gray, rose, smoky
• H = 7 (on Moh’s scale of 1-10)
• 6-sided prisms
• Conchoidal fracture
• Not chemically reactive
Figure 4-8 Atomic Structure of Quartz
3D network of Si4+ and O2- tetrahedra that
share oxygen atoms. The arrangement
gives quartz crystals distinctive form.
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Environmental/Health Risk
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Tiny particles of quartz enter lungs
Particles get stuck in openings
Cause inflammation and nodular lesions
Lungs deteriorate
Shortness of breath, fever
Silicosis: pneumonoultramicroscopicsilicovolcanokoniosis
e.g., Hawk’s Nest, West Virginia
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Granite
Granite—the material
from which the faces
on Mt. Rushmore were
carved—is an
aggregate of:
• quartz
• potassium feldspar
• plagioclase feldspar
• biotite
FIGURE 4-9 Granite: a Common Rock in Continental Crust
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Feldspars
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Potassium-rich KAlSi3O8
Plagioclase (Na,Ca)(Si,Al)4O8
White, gray, pinkish
H = 6 (on Moh’s scale of 1-10)
4-sided prisms
2 cleavages at 90º
Conchoidal fracture
Crystallizes over wide range of
temperatures
Figure 4-11 Potassium feldspar (a) and plagioclase feldspar
(b) are very common rock-forming minerals. These have been
broken along cleavages to form smooth, planar surfaces.
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Weathering of Feldspars
• Feldspars form at high temperatures and, hence, are not
stable at Earth’s surface, where lower temperatures and
pressures combine with interactions with the hydrosphere,
atmosphere, and biosphere to cause minerals to change into
minerals more stable at these conditions.
• These changes are called Chemical and Physical
Weathering
• Two examples are:
1. Hydrolysis = reaction of water (H2O) with minerals to form
new minerals (many with water in their atomic structures)
2. Dissolution = chemical (atomic) constituents are
dissolved and removed
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Feldspars Weather to Produce
Clays and Micas
Figure 4-12 Clays have a layered
atomic structure, not strongly
bonded. Water can occupy space in
the structure. They expand (wet) and
contract (dry), thus making poor
foundations.
Figure 4-13 Micas are silicate
minerals whose internal structures
include a plane with very weak bonds.
They easily break (cleave) into sheets
along this plane. Biotite (dark mica) is
an iron-bearing mineral. Muscovite
(silvery mica) is potassium-rich.
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Ferromagnesian Minerals
Fe and Mg (similar in size, 2+
charge)—can substitute in mineral
structures
Olivine (Mg, Fe)2SiO4
Greenish, H=6, variable density
conchoidal fracture (like quartz)
Pyroxene (Mg, Fe, Ca)2 Si2O6
Dark, H=6, dense
short rectangular prisms
so have 2 cleavages at 90o
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Figure 4-15 Olivine (a) and
Pyroxene (b) are ferromagnesian
minerals that are common in mafic
rocks like basalt and gabbro.
Weathering of Ferromagnesian
Minerals
• Olivines, pyroxenes, and amphiboles are even less stable at Earth’s
surface than the feldspars. When they interact with the hydrosphere
and atmosphere, they hydrolyze to form serpentine minerals.
• Chrysotile is an elongate, fibrous serpentine mineral—the principal
mineral in asbestos—and is heat-resistant and quite flexible.
Figure 4-16 Chrysotile Ferromagnesian
minerals hydrolyze to form many soft
serpentine minerals. One of these, the
fibrous serpentine mineral chrysotile, is
the principal mineral in asbestos.
Figure 4-18 Tremolite A dangerous
asbestiform amphibole. The elongate fibrous
crystals of the amphibole mineral tremolite
have caused serious health problems.
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Ferromagnesian Minerals
• Biotite K(Mg,Fe)3(Al,SiO3010)(OH)2
• Hydrated, black, H=3, mod.
dense sheet structure (1 cleavage)
• Hornblende (Ca,Na)2-3(Mg,Fe,Al)5
Si6(Si,Al)2O22(OH)2O6
• Dark, H=5-6, mod. dense
elongate rectangular prisms have
2 cleavages @ 56 and 124°
Figure 4-17 Biotite and
hornblende (b) are hydrated
ferromagnesian minerals.
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Other Minerals, Sulfides, Oxides,
and Carbonates
Sulfides—combinations of ions (especially metals with positive charges)
with sulfur (2- charge)
Examples:
PbS
Lead Sulfide
ZnS
Zinc Sulfide
FeS2
Iron Sulfide
Galena
Sphalerite
Pyrite
Figure 4-19 Pyrite or “Fool’s Gold”
• Some Earth systems concentrate sulfide minerals into
metal-rich deposits—which are the principal source of metals
through mining.
• Processing of these minerals to extract the metals is
implicated in many environmental issues.
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Sulfides, Oxides, and Carbonates
Oxides—combinations of ions (especially metals with positive charges)
with oxygen (2- charge)
TiO2
Titanium oxide
SnO2 Tin Oxide
Fe3O4 Iron Oxides
Fe2O3
FeO(OH)
Rutile
Cassiterite
Magnetite
Hematite
Goethite
Figure 4-20 Oxidation of Febearing minerals gives rocks,
soils rusty color.
• Oxides tend to be more stable, less chemically reactive on Earth’s surface
than other minerals. Like quartz, they commonly survive weathering and
can become components of sand.
• Several minerals at Earth’s surface react with oxygen. The positive ions in
these minerals combine with oxygen to form oxide minerals. This chemical
reaction is oxidation. An example is rust, combination of hematite,
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goethite.
Sulfides, Oxides, and Carbonates
Carbonates—combinations of positively charged ions
(Ca2+,Mg2+,Fe2+) ions with negatively charged carbonate (CO32-)
CaCO3 : Calcite
(Ca,Mg)CO3: Dolomite
• These minerals are generally soft (H = 3-4), light-colored, with good
cleavages (often in 3 directions), making rhombs.
• They are also prone to dissolve in acid, including acidic rain over time.
• Landscapes (called Karst Terrains) underlain by calcite-rich rocks show
many dissolution features (e.g., caves, sinkholes, disappearing
streams).
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Karst
• Carbonate minerals generally form by
precipitating from oceans (with a large
concentration of Ca2+ and CO32-).
Marine animals also precipitate
carbonate minerals from seawater to
make shells or other structures (e.g.
coral reefs).
• These die and sink to the ocean floor.
Accumulations of carbonate material
eventually form limestone.
Figure 4-22 Dissolution of the
Geosphere Produces Karst Terrain
Dissolution of carbonate minerals
leads to the formation of caves such
as Mammoth Cave in Kentucky (a),
hummocky landscapes (b), sinkholes
that suddenly collapse (c).
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Igneous Rocks
• Crystallize/solidify from molten rock = magma
• Felsic—Feldspar and silica
(Si, Na, K)
>63% SiO2
• most characteristic of continental crust
• Mafic—Magnesium iron (ferric) (Fe, Mg, Ca)
45–55% SiO2
• most characteristic of oceanic crust—ferromagnesian
minerals
• Intermediate—common in subduction zones
55–63% SiO2
• Intrusive (plutonic)—erupt and crystallize rapidly, small
crystals, basalt
• Extrusive (volcanic)—cool slowly underground, large
crystals, gabbro
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(a) Basalt 30 micron thick slice
of basalt photographed through
a microscope using transmitted
cross-polarized light. Light gray
rectangular crystals are feldspar;
olivine and pyroxene are variably
colored irregular crystals.
Individual crystals are extremely
small, due to rapid cooling of the
lava after eruption.
Figure 4-23
(b) Gabbro White crystals are
feldspar and dark crystals are
pyroxene. Both the basalt and
gabbro have the same
composition, but the gabbro is
coarser-grained than the basalt
as a consequence of much
longer cooling times.
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Oceanic crust includes:
• deep-sea sediments
• basalt lava flows
• sheeted basalt dikes
• gabbro intrusions
• some ultramafic rocks
Figure 4-24 Oceanic Crust Has a
Well-defined Internal Structure.
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Continental Crust
• More compositionally diverse than oceanic crust
• Range from mafic (lower) to felsic (upper)
• Ave. composition is intermediate between these two end members,
older, more structurally and compositionally complex
• Originally basaltic—melted producing intermediate
compositions
• Today—oceanic crust is altered by hydrolysis with seawater—
recrystallizes during subduction, releasing H2O, melting the crust
• This melting forms intermediate (andesitic) magmas
characteristic of subduction zones. These magmas are:
• Often explosive
• Release volatiles (H2O, CO2, H2S)
• Andesite—intermediate/mafic, plagioclase + pyro
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Rock Cycle
Figure 4-25
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Weathering
• Set of physical and chemical processes that change rocks at
Earth’s surface
• Uplift causes rocks to be exposed, as outcrops, on the Earth’s
surface
• Expansion (from decompression) breaks rocks along fractures
called joints
• Physical Weathering—breaks the rocks into smaller pieces with
higher surface area to volume ratio; principally from action of
freezing water
• Frost wedging: expansion of H2O in cracks breaks rock
• Root wedging: growth of plant roots breaks rocks along cracks
• Chemical Weathering—breaks down rocks and change
composition
• Hydrolysis
• Oxidation
• Dissolution
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(a) Frost wedging: the repeated expansion
of water as it freezes in cracks and
disaggregates (breaks) rocks.
(b) Root wedging: growth of plant roots in
cracks breaks rocks apart.
(c) Chemical weathering: processes such as
hydrolysis, oxidation, dissolution, which
decompose rocks.
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Figure 4-27
Weathering Processes
Erosion
• Transportation of geosphere materials by movements
of water, wind, and ice (glaciers)—primarily by gravity
• Glaciers:
• scrape material off valleys as they flow downslope
• push material in front as they advance
• deposits of rock debris from glaciers are called moraines
• Streams and rivers: the principal movers of rock debris
• Fast, deep streams may carry and move large boulders
• Abrade and pluck material from the valley walls
• Rock material rolled and bounced along the bottom of a
stream/river is the bedload
• Smaller sediments may be suspended, making the stream
muddy
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Sedimentary Rocks
Sedimentation, Lithification
• Sediment
• Clastic sediments: composed of fragments of material
• Chemical sediments: precipitate from solutions
• Clastic Sediments
• Transported—mainly by moving water (some by wind) from original
source
• Deposited—primarily in sedimentary basins, where water velocity
drops
• Clast size—depends on transport distance, velocity, strength
gravel
sand
silt
clay/mud
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Figure 4-29 Sedimentation
(b) Rivers carry sediment to the coast.
Figure 4-28 Erosion (a) Sediment transport starts with rocks falling in steep
terrain. (c) Fast-moving streams carry and abrade larger rocks.
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Figure 4-30 Clastic Sedimentary Rocks
When sediments become deeply buried, they
lithify. (a) Muddy sediment turns into shale. (b)
Sand becomes sandstone. (The rusty stains in
this specimen define individual layers or beds.)
(c) Gravel forms rocks called conglomerate.
Figure 4-29 (a) Clastic sediments range in size
from tiny clay particles to sand and gravel.
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Chemical Sedimentary Rocks
• These minerals generally precipitate where evaporation
has increased their concentration in seawater, so the rocks
they form are called evaporites.
• Limestone—Most common chemical sediment is calcium
carbonate, the mineral calcite (CaCO3). Where calcite is
buried and lithified it becomes limestone. There are many
types:
• Fossiliferous
• Oolitic
• Crystalline
• Microcrystalline (micrite)
• Gyprock—mineral gypsum (CaSO4)
• Rock Salt—minerals halite (NaCl) and sylvite (KCl)
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Figure 4-31 Limestone: A
Marine Sedimentary Rock
Limestone is derived from the
mineral calcite, a form of calcium
carbonate. Calcite that
precipitates on the seafloor, or
accumulates there in the
remains of marine organisms,
becomes limestone when it is
lithified.
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Metamorphism
• Rocks changed from higher temperature and
pressure. Any rock can become metamorphosed
(igneous, sedimentary, metamorphic).
• minerals formed at the surface not stable at
higher T and P
• recrystallize to form minerals stable at higher T
and P
• recrystallization largely involves dehydration
reactions
• new minerals grow in orientations influenced by
P—metamorphic textures
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Metamorphism (cont.)
• Typical metamorphic rocks:
• Schist: usually contains flaky mica minerals—oriented parallel to
one another
• foliation = strongly 2D sheeted structure, termed schistosity
• sedimentary rocks (shale, sandstone) are examples of schist
protoliths
• Gneiss: contains discontinuous layers (called lenses) of larger
minerals (generally quartz and feldspar) separated by finer-grained,
schistose layers
• forms at higher T and P than many schists
• gneiss can form from any rock, but many form from clastic
sedimentary rocks
• Marble: metamorphosed limestone (mineral still is calcite)
• the original calcite minerals have been recrystallized
• tend to be larger than the original ones in the limestone
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Figure 4-32 Metamorphic Rocks
In schist (a), generally formed
from sedimentary rocks like shale
or sandstone, crystals of new
minerals such as biotite are
oriented parallel to each other.
This arrangement gives the rock a
well-developed foliation.
In gneiss (b), typically formed at
higher temperatures and pressures
than schist, new minerals tend to
be coarser and segregated into
discontinuous layers and lenses.
The folded layers in this gneiss are
a few to several centimeters across
(about 1–10 in).
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Using Rocks
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Commercial and residential buildings
Highways, bridges, sidewalks, and parking lots
Factories and power generation facilities
Water storage, filtration, and delivery systems
Wastewater collection and treatment systems
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FIGURE 4-36 Distribution of Aggregate Mining
Aggregate mining operations can be found near most communities in the
United States.
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Aggregate
• Aggregate = sand, gravel, and crushed stone—“common rock”
• incorporated into cement and asphalt
• spread on roadways and building sites to help stabilize the ground
• Our need for aggregate is increasing, especially for basic infrastructure
• bridges, highways, transit construction, etc.
• cheap to mine and process
• but transporting is costly
Figure 4-35 Past and Future
Use of Aggregate Our need for
aggregate, especially crushed
stone, is increasing rapidly.
It is estimated that by 2020 we will
be using more than twice as much
as we did in 1960.
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Issues with Aggregate Mining
• Physical disturbances
• Aggregate must be physically removed from its
source—leaving physical disturbances such as
quarries or pits, the removing of natural vegetation
• Mitigate by developing visibility barriers, ensuring
well-planned and orderly oper ations, and
reclaiming areas as operations proceed
• Slope contouring, new soil, revegetation
(reclamation)
• Aggregate pits and quarries can become lakes for
recreation and wildlife habitat
• Disturbed terrain can become parks, gardens, or
even golf courses
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Issues with Aggregate Mining (cont.)
• Dust and noise
• Aggregate mining, breaking up rocks blasting,
hauling, and crushing
• Dust can cause respiratory illnesses
• Air quality monitoring and compliance with
regulations required
• Noise from blasting and equipment
operations a significant concern
• Congestion and safety
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Aggregate Mining in Your Neighborhood
How would you answer the following questions?
• Do you think that the annual and per capita consumption of
aggregate accurately reflects your use of these resources?
• What do you think the future aggregate needs of the U.S. are
going to be? What are the more important factors that influence
these needs?
• Where do you think new aggregate resources should come
from?
• Do you think aggregate mining should take place in your
community?
• Do you think that mitigation measures such as reclamation can
satisfactorily address the environmental concerns associated
with aggregate mining?
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