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ENGINEERING GEOLOGY
SPRING 2017
LECTURE THREE: MINERALS
PREPARED BY
DR. KHAYYUN A. RAHI
DEPARTMENT OF ENVIRONMENTAL ENGINEERING
MINERALS: BUILDING BLOCKS OF
ROCKS
• By definition a mineral is:
• Naturally occurring
• An inorganic solid
• Ordered internal molecular structure
• Definite chemical composition
• Rock
• A solid aggregate of minerals
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COMPOSITION OF MINERALS
• Elements
• Basic building blocks of minerals
• Less than 100 are known (92 are
naturally occurring)
• Atoms
• Smallest particles of matter
• Retains all the characteristics of an
element
COMPOSITION OF MINERALS
• Atomic structure
• The central region is called the nucleus.
–Consists of protons (+ charges) and neutrons
(- charges)
• Electrons
–Negatively charged particles that surround the
nucleus
–Located in discrete energy levels called shells
• Atomic number = number of protons in nucleus
• Atomic mass = weight of protons and neutrons
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STRUCTURES OF:
(a)
Proton
(a) a hydrogen atom,
in which an electron
orbits a single proton,
and,
(b) an oxygen atom, in
which 8 electrons
orbit a dense nucleus
containing 8 protons
and 8 neutrons.
Electron
(b)
Proton
Nucleus
Neutron
Electron
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ATOMS 3
• Ions: + or – charge from gain or loss of an
electron(s)
• Cation: positively charged, example: Na+
• Anion: negatively charged, example: Cl• Cations and anions often combine in minerals,
example: NaCl (halite)
• Isotopes: forms of same element with different
atomic masses = different numbers of neutrons
• Unstable isotopes emit particles and energy in
a process known as radioactive decay
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MINERAL IDENTIFICATION
• Color: Elementary property. Generally unreliable.
• Streak: Color observed by scratching the mineral
on a porcelain plate.
• Mohs hardness scale: 1 (softest) – 10 (hardest)
• Cleavage: characteristic way minerals split
• Fracture: patterns distinctive for many minerals
that don’t cleave
• Luster: how a mineral reflects light
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Quartz (SiO2) Exhibits a Variety of
Colors
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STRUCTURE OF MINERALS
• Polymorphs
• Minerals with the same composition but
different crystalline structures
• Examples include diamond and graphite
»Phase change is when one
polymorph changes into another.
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DIAMOND AND GRAPHITE—
POLYMORPHS OF CARBON
MINERAL GROUPS
• Nearly 4000 minerals have been named
• Rock-forming minerals
• Common minerals that make up most
of the rocks of Earth’s crust
• Only a few dozen members
• Composed mainly of the eight
elements that make up more than
98% of the continental crust.
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ELEMENTAL ABUNDANCES
IN CONTINENTAL CRUST
Most Common:
Oxygen – O
Silicon – Si
Aluminum – Al
Iron – Fe
MINERAL GROUPS
• Silicates
• Most important mineral group
–Comprise most rock-forming minerals
–Very abundant due to large percentage of
silicon and oxygen in Earth’s crust
• Silicon–oxygen tetrahedron
–Fundamental building block
–Four oxygen ions surrounding a much
smaller silicon ion
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TWO ILLUSTRATIONS OF THE
SI–O TETRAHEDRON
MINERAL GROUPS
• Common silicate minerals
• Light silicates: feldspar group
–Most common mineral group
–Exhibit two directions of perfect
cleavage at 90 degrees
–Orthoclase (potassium feldspar) and
plagioclase (sodium and calcium
feldspar) are the two most common
members.
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PLAGIOCLASE FELDSPAR
MINERAL GROUPS
• Common silicate minerals
• Light silicates: quartz
–Only common silicate mineral
composed entirely of oxygen and
silicon
–Hard and resistant to weathering
• Light silicates: muscovite
–Common member of the mica family
–Excellent cleavage in one direction
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MINERAL GROUPS
• Common silicate minerals
• Light silicates: clay minerals
–Clay is a general term used to
describe a variety of complex
minerals.
–Exhibit a sheet or layered structure
–Most originate as products of
chemical weathering.
MINERAL GROUPS
• Common silicate minerals
• Dark silicates: olivine group
–High temperature Fe–Mg silicates
• Dark silicates: pyroxene group
–Augite is the most common mineral in
the pyroxene group
• Dark silicates: amphibole group
–Hornblende is the most common
mineral in the amphibole group.
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Some common
rock-forming
silicate minerals:
(a) feldspar,
(b) quartz,
(c) muscovite,
(d) hornblende.
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MINERAL GROUPS
• Important non-silicate minerals
•Typically divided into classes
based on anions
•Comprise only 8% of Earth’s
crust
•Often occur as constituents in
sedimentary rocks
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MINERAL GROUPS
• Important non-silicate minerals
•Carbonates
–Primary constituents in
limestone and dolostone
–Calcite (CaCO3) and dolomite
CaMg(CO3)2 are the two most
important carbonate minerals.
MINERAL GROUPS
• Important non-silicate minerals
• Many non-silicate minerals have economic
value.
• Examples:
–Hematite (oxide mined for iron ore)
–Halite (halide mined for salt)
–Sphalerite (sulfide mined for zinc ore)
–Native copper (native element mined for
copper)
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Magnetite and Hematite Are Both Iron Oxides
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END OF LECTURE 3
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