Chapter 2
Rocks and Minerals
A First Look
The differences in the physical properties of
rocks, minerals, and soils determine their
suitability for different purposes – extraction of
water or of metals, construction, manufacturing,
waste disposal, agriculture, and other uses
Atoms
• Smallest particle into which an element can be
divided while still retaining the chemical
characteristics of that element
• Composed of a nucleus surrounded by
electrons
– Nucleus is composed of protons (+) and neutrons
(0)
– Number of protons defines the chemical element
and 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
Figure 2.1 Schematic drawing of atomic structure
Elements and Isotopes
• Element – substance composed of atoms with the
same number of protons
• All nuclei, except the simplest hydrogen atoms,
contain neutrons
• The number of neutrons is similar to or somewhat
greater than the number of protons
• Isotopes – number of neutrons for and element may not be
the same; variable numbers of neutrons possible
– Atomic Mass Number is the number of protons and
neutrons in the elements nucleus
– Some isotopes have more neutron and are heavier (carbon14 has 6 protons and 8 neutrons)
– Some isotopes have fewer neutrons and are lighter (carbon12 has 6 protons and 6 neutrons)
Ion
• An atom that is positively charged or
negatively charged
– Anion have gained electrons (-); has more
electrons relative to the number of protons (+)
– Cation has lost electrons (-); has fewer electrons
relative to the number of protons (+)
• The electrical attraction of ions will cause an
ionic bond to form between oppositely
charged ions.
– Na+ + Cl- = NaCl (halite)
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
MINERALS
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Naturally occurring
Inorganic
Solid element or compound
Definite chemical composition
Regular internal crystal structure
Identified by recognizing different physical
properties
Figure 2.3A
Figure 2.3B
Identifying Minerals
• The two fundamental characteristics of a
mineral 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
Mineral Physical Properties
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Color
Hardness
Cleavage
Luster
Density
Crystalline Form
Mineral Composition
Silicate Group
• Silicate group – variety of compounds based
on silicon and oxygen
 Quarts – glass manufacturing
 Feldspar – ceramic manufacturing
 Mica
• Muscovite (white mica)
• Biotite (dark mica)
 Clays – used as drilling mud, in building
materials, and as a soil modifier
• Ferromagnesian silicates
 Olivine – peridot (semiprecious gem)
 Garnet - abrasives
 Asbestos – industrial products
Figure 2.6
Figures 2.7 a and b
Mineral Composition
Nonsilicates
• Carbonates – CO3
– Useful for building materials and manufacturing
• Sulfates – SO4
– Useful for building materials
• Sulfides – S
– Host for many metallic ores (Pb, Cu, Zn, and others)
• Oxides – any metal combined with oxygen
– Iron and aluminum ores
• Native elements – minerals composed of single
element
– Carbon as diamond and graphite
– Cooper, gold, silver, or platinum
Figures 2.2 c and d
Figures 2.3 a and b
Figure 2.4
Figures 2.5 a and b
Rocks – formed 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
Igneous Rocks
• Magma, at high enough temperatures,
rocks and minerals can melt, and the
natural hot, molten rock material is called
magma
• Silicates are the most common minerals,
and magmas are thus rich in silica.
Magmas also contain some dissolved
water and gases, and include some solid
crystals suspended in the melt
• An igneous rock is a rock formed by the
solidification and crystallization of a
cooling magma
Igneous Rocks
• Rocks formed from hot, molten rock
material – “fire” rocks
• Usually composed of silicate minerals and
some dissolved gases and water
• Molten materials are very hot
– Plutonic rocks form if magma does not flow
onto surface; coarse crystals will grow
– Volcanic rocks form if magma flows onto
surface as lava; glass often forms
Figures 2.10 a and b
Igneous Rocks
• Granite is the most widely known example of a
plutonic rock, consisting of quartz, feldspars, and
some ferromagnesian minerals or other silicates
• Granites show the characteristic of a plutonic
rock: the coarse and interlocking crystals
• Lava, a magma that flows out on the earth’s
surface while still wholly or partly molten
• Volcanic, an igneous rock formed at or close to
the earth’s surface
• Basalt, the most common volcanic rock, rich in
ferromagnesian minerals and feldspar
Weathering of Rocks
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Chemical weathering
Physical weathering
Sediments
Ions for cements
Sedimentary Rocks
• Sediments are produced by weathering of preexisting rocks and minerals
• Sediments are loose, unconsolidated
accumulations of mineral or rock particles
• Sediments are eroded, transported, and deposited
in many sedimentary environments
• The sediments will be buried and experience
lithification
• Lithification involves compacting the sediments
with burial and cementation of the sediments
forming a sedimentary rock
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
earth’s surface and at temperatures close to
ordinary surface temperatures.
Types of Sedimentary Rocks
• Clastic sedimentary rocks
– Formed by the lithification of mechanically broken up
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 form thick
deposits
• Examples: Halite, Calcite, and Gypsum
Figures 2.11 Sedimentary Rocks
Figures 2.11 Sedimentary Rocks
Metamorphic Rocks
• “Changed form” rock
• Rock formed from pre-existing rock or minerals
• Heat, pressure, and chemical 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
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 of
metamorphism: burial, magma, mountainbuilding, and plate tectonic movement
• The sources of elevated pressures of
metamorphism: burial, mountain-building, and
plate tectonic movement
Types of Metamorphism
• Contact metamorphism – localized
metamorphism of rocks adjacent to a
magma chamber
• Regional metamorphism – large scale
stressing and heating of a rock by deep
burial or continental plates moving and
colliding
Common Metamorphic Rocks
• Any kind of preexisting rock (another rock) can
be metamorphosed
• Foliation: when a rock is subjected to directed
stress, its minerals form elongated/platy crystals
and line up parallel to each other
• Metamorphic rocks without foliation do not
directed stress
– Marble is metamorphosed limestone
– Quartzite is metamorphosed quartz-rich sandstone
• Metamorphic rocks with foliation show directed
stress or pressure
– Slate – low grade foliated metamorphic rock
– Schist and Gneiss (nice) – high grade metamorphic
rocks
Figures 2.12 Metamorphic rocks have undergone
mineralogical, chemical, and/or structural change
Figures 2.12 Metamorphic rocks have undergone
mineralogical, chemical, and/or structural change
The Rock Cycle
• Three rock groups on the basis of their mode
of origin: igneous, sedimentary, and
metamorphic
• Shows the interrelationships among the
three rock types
• Rocks of any type can be transformed into
rocks of another type or into another distinct
rock of the same general type through the
geologic processes
• Rocks are continually being changed by
geological processes
The Rock Cycle
• Earth as a system: the rock cycle
• Magma, a molten material formed inside Earth
• Crystallization, magma cools and solidifies
• Igneous rock, formed by “fire” underneath
• Weathering, transportation, and deposition
• Sediment
• Lithification
• Sedimentary rock
• Metamorphism
• Metamorphic rock
• Melting
• Magma
The Rock Cycle
• Earth as a system: the rock cycle
• Full cycle does not always take place due to
"shortcuts" or interruptions
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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
Fig. 2.13 The Rock Cycle
The Rock Cycle
• The Essence of the Rock Cycle
• Igneous rocks, formed from magma
• Sedimentary rocks, formed from lowtemperature accumulations of particles or
by precipitation from solution
• Metamorphic rocks, formed from
preexisting rocks through the change of
temperature and pressure
• Geologic processes working on old rocks
change the old rocks into new and
different ones, and thus all kinds of rocks
are interrelated in a sense