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Rocks and Minerals: A First Look
Chapter 2
The differences in the
physical properties of
rocks, minerals, and soilsdetermine their suitability
for different purposes
extraction of water or of
metals, construction,manufacturing, waste
disposal, agriculture, and
other uses
Illinois Fluorite, photo by J. Carr
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Atoms Smallest particle into which an element can be
divided while still retaining the chemicalcharacteristics of that element
Composed of a nucleussurrounded byelectrons Nucleus is composed of protons(+) and neutrons
(0)
Number of protons defines the chemical elementand atomic number( H = 1, He = 2, Li = 3, )
Number of neutron adds mass to the atom Number of electrons (-) orbiting nucleus determined
by the number of positively charged protons;
Negatively charged electrons balance the positive
charges of the protons
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Figure 2.1 Schematic drawing of atomic structure
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Elements and Isotopes
Elementsubstance composed of atoms with thesame number of protons
All nuclei, except the simplest hydrogen atoms,contain neutrons
The number of neutrons is similar to or somewhatgreater than the number of protons
Isotopesnumber of neutrons for an element may not be thesame; variable numbers of neutrons possible
Atomic Mass Numberis the number of protons and
neutrons in the elements nucleus Some isotopes have more neutrons and are heavier
(carbon-14 has 6 protons and 8 neutrons)
Some isotopes have fewer neutrons and are lighter (carbon-12 has 6 protons and 6neutrons)
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Ion
An atom that is positively charged or
negatively charged
Anionhas gained electrons (-); has more
electrons relative to the number of protons (+) Cationhas lost electrons (-); has fewer electrons
relative to the number of protons (+)
The electrical attraction of ions will cause an
ionic bondto form between oppositelycharged ions.
Na++ Cl-= NaCl (halite)
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Compounds
Mixing of two or more chemical elements
in particular proportions that have
distinctive physical properties
Elements will bond because of electrical
attraction, forming ionic bonds, or the
atoms may share electrons, forming
covalent bonds
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MINERALS
Naturally occurring
Inorganic
Solid element or compound Definite chemical composition
Regular internal crystal structure
Identified by recognizing different physicalproperties
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Figure 2.3B
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Identifying Minerals
The two fundamental characteristics of amineral are its chemical composition and
its crystal structure
Analyze the mineral composition Technology based
Measure crystal structure and symmetry
Technology based Observe and measure physical and
special properties
Easy for humans to see and recognize
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Mineral Physical Properties
Color
Hardness
Cleavage
Luster
Density
Crystalline Form
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Figure 2.6
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Figures 2.7 a and b
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Mineral CompositionNonsilicates
CarbonatesCO3 Useful for building materials and manufacturing
SulfatesSO4 Useful for building materials
SulfidesS Host for many metallic ores (Pb, Cu, Zn, and others)
Oxidesany metal combined with oxygen Iron and aluminum ores
Native elementsminerals composed of singleelement Carbon as diamond and graphite
Copper, gold, silver, or platinum
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Figures 2.2 c and d
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Figures 2.3 a and b
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Figure 2.4
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Figures 2.5 a and b
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Rocksformed from Minerals
A solid aggregate of one or more
minerals, or mineral materials
Consists of many mineral grains or
crystals forming a solid mass
Each rock contains a record of its own
history
Three broad categories
Igneous
Sedimentary
Metamorphic
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Igneous Rocks
Magma, at high enough temperatures,
rocks and minerals melt, and the naturalhot, molten rock material is called magma
Silicates are the most common minerals,
and magmas are thus rich in silica.Magmas also contain some dissolvedwater and gases, and include some solidcrystals suspended in the melt; iron
content is variable and this variability is thebasis for igneous rock classification
An igneous rock is a rock formed by thesolidification and crystallization of acoolin ma ma
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Igneous Rocks
Rocks formed from hot, molten rock
material
Usually composed of silicate minerals and
some dissolved gases and water
Molten materials are very hot
Plutonicrocks form if magmacools inside
earths crust (does not flow onto surface);
coarse crystals will grow Volcanicrocks form if magma flows onto
surface as lava; glass often forms
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Figures 2.10 a and b
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Igneous Rocks
Felsic;
low iron
light toned
Intermediate Mafic;
high iron
dark toned
Ultramafic
Volcanic;extrusive;
aphanitic
Rhyolite Andesite Basalt Eclogite
Plutonic;
intrusive;
phaneritic
Granite Diorite Gabbro Peridotite
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Weathering of Rocks
Chemical weathering
Physical weathering
Sediments Ions for cements
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Sedimentary Rocks
Sediments are produced by weathering of pre-
existing rocks and minerals
Sediments are loose, unconsolidated
accumulations of mineral or rock particles
Sediments are eroded, transported, and depositedin many sedimentary environments
The sediments will be buried and experience
lithification
Lithificationinvolves compacting the sediments
with burial and cementation of the sediments
forming a sedimentary rock
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Sedimentary Rocks
Gravity plays a role in the formation of all
sedimentary rocks.
Layering is a very common feature of
sedimentary rocks and is used to identify the
origins of sedimentary rocks.
Sedimentary rocks can yield information
about the settings in which the sediments
were deposited. Sedimentary rocks are formed at or near the
earths surface and at temperatures close to
ordinary surface temperatures.
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Types of Sedimentary Rocks
Clastic sedimentary rocks Formed by the lithification of mechanically weathered
pieces of rocks and minerals Grain sizes range from boulder, gravel, sand, silt, and mud
Grains are continually broken down in size and shape
until deposited Once deposited these clastic particles a cemented
Chemical sedimentary rocks Chemical process occur in water bodies such as
lakes, seas, or oceans Minerals precipitate from the water and form thick
deposits Examples: Halite, Calcite, and Gypsum
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Figures 2.11 Sedimentary Rocks
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Metamorphic Rocks
Changed form rock
Rock formed from pre-existing rock or minerals
Heat, pressure, and chemically active fluids
cause changes in rock
Heat increases as a rock is buried or is close to
a magma chamber
Pressure increases with burial or collision
between moving continents Fluids become heated and circulate with burial
or with location near a magma chamber
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Metamorphic Rocks
The temperatures required to form metamorphic
rocks are below magmatic temperatures Significant changes can occur in a rock at
temperatures well below melting
Temperature and pressure can cause the
minerals in the rock to recrystallize Pressure may cause the rock to be deformed
The sources of elevated temperatures ofmetamorphism: burial, magma, mountain-building, and plate tectonic movement
The sources of elevated pressures ofmetamorphism: burial, mountain-building, andplate tectonic movement
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Types of Metamorphism
Contact metamorphismlocalized
metamorphism of rocks adjacent to a
magma chamber
Regional metamorphismlarge scale
stressing and heating of a rock by deep
burial or continental plates moving and
colliding
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Common Metamorphic Rocks Any kind of preexisting rock (another rock) can
be metamorphosed Foliation:when a rock is subjected to directedstress, its minerals form elongated/platy crystalsand line up parallel to each other
Metamorphic rocks without foliationdo not showdirected stress Marble is metamorphosed limestone
Quartzite is metamorphosed quartz-rich sandstone
Metamorphic rocks with foliationshow directedstress or pressure Slatelow grade foliated metamorphic rock
Schist and Gneiss (nice)high grade metamorphic
rocks
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Figures 2.12Metamorphic rocks have undergonemineralogical, chemical, and/or structural change
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Figures 2.12 Metamorphic rocks have undergone
mineralogical, chemical, and/or structural change
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The Rock Cycle
Three rock groups on the basis of their modeof origin: igneous, sedimentary, andmetamorphic
Shows the interrelationships among the
three rock types Rocks of any type can be transformed into
rocks of another type or into another distinctrock of the same general type through thegeologic processes
Rocks are continually being changed bygeological processes
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The Rock Cycle
Earth as a system: the rock cycle
Full cycle does not always take place due to
"shortcuts" or interruptions
e.g., Sedimentary rock melts
e.g., Igneous rock is metamorphosed e.g., Sedimentary rock is weathered
e.g., Metamorphic rock weathers
Through time, geologic processes acting
on older rocks change them into new
and different ones so that, in a sense, all
kinds of rocks are interrelated
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Fig. 2.13 The Rock Cycle
Th R k C l
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The Rock Cycle
The Essence of the Rock Cycle
Igneous rocks, formed from magma Sedimentary rocks, formed from low-
temperature accumulations of particles or
by precipitation from solution Metamorphic rocks, formed from
preexisting rocks through the change oftemperature and pressure
Geologic processes working on old rockschange the old rocks into new anddifferent ones, and thus all kinds of rocks