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Earth: An Introduc/on to Physical Geology, 10e Tarbuck & Lutgens © 2011 Pearson Education, Inc.
Ma<er and Minerals Earth, 10e -­‐ Chapter 3 Hernan Santos University of Puerto Rico Mayagüez Campus © 2011 Pearson Education, Inc.
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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Minerals: Building Blocks of Rocks •  By definition a mineral is:
•  Naturally occurring-­‐ are formed by natural, geologic processes. Consequently synthe:c diamonds and rubies, as well as a variety other useful material produced in the laboratory are not considered minerals.
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Minerals: Building Blocks of Rocks •  By definition a mineral is:
•  Solid. Minerals are solids within the
temperature range normally experience at
Earth’s surface. Thus, ice (frozen water) is
considered a mineral, whereas liquid water and
vapor as well as mercury are not.
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Minerals: Building Blocks of Rocks •  By definition a mineral is:
•  Orderly crystalline structure. Atoms are
arranged in an orderly, repetitive manner. Some
naturally occurring solids, like volcanic glass
(obsidian), lack repetitive atomic structure are
not considered minerals.
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Minerals: Building Blocks of Rocks •  By definition a mineral is:
•  Well-defined chemical composition. Most
mineral are chemical compounds having
compositions that are given by their chemical
formula. The mineral pyrite is FeS2 is
composed of 1 iron and 2 sulfur.
•  Opal is SiO2 (n H2O) - Mineral gel
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Minerals: Building Blocks of Rocks •  By definition a mineral is:
•  Generally inorganic. Sugar, a crystalline solid
that comes from sugarcane are not considered
minerals. However many marine animals
secrete inorganic compounds, such as calcium
carbonate (calcite), in the form of shells and
corals. If these material are buried and become
part of the rock record, they are considered
minerals.
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Composi/on 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
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Composi/on 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
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Structure of an Atom © 2011 Pearson Education, Inc.
Composi/on of Minerals •  Except for a group of elements known as the
noble gases, atoms bond to one another
under the conditions (temperatures and
pressures) that occur on Earth.
•  Some atoms bond:
–  To form ionic compounds
–  To form molecules
–  To form metallic substances
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Composi/on of Minerals •  Experiments show that the forces holding
atoms together and that bond atoms to each
other are electrical forces.
•  Atoms can have several layers of electrons. The first shell
can only hold 2 electrons. In the second and higher shells a
stable configuration occurs when the valance shell contains
8 electrons.
•  Noble gases such as Helium (2 electron in the first shell)
and neon and argon (8 electrons in the outer shell) tend not
to react.
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Composi/on of Minerals •  When an atom’s outer shell does not contain
eight electrons, it is likely to chemically
bound to other atoms to fill its shell.
•  A chemical bond is the transfer or sharing
of electrons that allows each atom to attain
a full valance shell of electrons.
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Composi/on of Minerals © 2011 Pearson Education, Inc.
Composi/on of Minerals •  Chemical bonding (enlaces)
•  Formation of a compound by combining two
or more elements
•  Ionic bonding
•  Atoms gain or lose outermost (valence)
electrons to form ions.
•  Ionic compounds consist of an orderly
arrangement of oppositely charged ions.
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Halite (NaCl)—An Example of Ionic Bonding 2+8+1
2+8+7
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Composi/on of Minerals •  Covalent bonding
•  Atoms share electrons to achieve electrical
neutrality.
•  Generally stronger than ionic bonds
•  Both ionic and covalent bonds typically occur
in the same compound.
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Composi/on of Minerals © 2011 Pearson Education, Inc.
Composi/on of Minerals •  Other types of bonding:
•  Metallic bonding
– Valence electrons are free to migrate among
atoms.
– Weaker and less common than other bonds
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Composi/on of Minerals •  Isotopes and radioactive decay (Cap-9)
•  Mass number = sum of neutrons + protons in
an atom.
•  An isotope is an atom that exhibits variation
in its mass number.
•  Unstable isotopes emit particles and energy
in a process known as radioactive decay.
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Structure of Minerals •  Minerals consist of an orderly array of
atoms chemically bonded to form a
particular crystalline structure.
•  The internal atomic arrangement in ionic
compounds is determined by ionic size.
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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 © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Primary diagnostic properties
•  Determined by observation or performing a
simple test
•  Several physical properties are used to
identify hand samples of minerals.
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Physical Proper/es of Minerals •  Crystallization
•  Crystal or crystalline refers to any natural
solid with an ordered, repetitive, atomic
structure.
Minerals form through the process of
crystallization in which molecules and/or ions
chemically bond to form an orderly internal
structure.
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Physical Proper/es of Minerals •  Crystallization
•  Crystal or crystalline refers to any natural
solid with an ordered, repetitive, atomic
structure.
Minerals form through the process of
crystallization in which molecules and/or ions
chemically bond to form an orderly internal
structure.
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Physical Proper/es of Minerals •  Crystallization
•  When a solution evaporates
•  Temperature changes
•  Due to biological processes
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Physical Proper/es of Minerals •  Crystal form
•  External expression of a mineral’s internal
structure
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Crystals of Pyrite © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Crystal form
•  Often interrupted due to competition for
space and rapid loss of heat
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Physical Proper/es of Minerals • 
Luster
•  Appearance of a mineral in reflected light
•  Two basic categories:
1.  Metallic
2.  Nonmetallic
•  Other descriptive terms include vitreous,
silky, or earthy.
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Galena (PbS) Displays Metallic Luster © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Color
•  Generally unreliable for mineral
identification
•  Often highly variable due to slight changes in
mineral chemistry
•  Exotic colorations of certain minerals
produce gemstones
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Quartz (SiO2) Exhibits a Variety of Colors © 2011 Pearson Education, Inc.
Quartz (SiO2) Exhibits a Variety of Colors © 2011 Pearson Education, Inc.
Color •  Malachite •  Sulfur •  Azurite © 2011 Pearson Education, Inc.
Color •  Sulfur-­‐for explosives, fungicides and fer:lizers •  Realgar-­‐ used for arsenic and to give fireworks the red color © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Streak
•  Color of a mineral in its powdered form
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Streak Is Obtained on an Unglazed Porcelain Plate © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Hardness
•  Resistance of a mineral to abrasion or
scratching
•  All minerals are compared to a standard
scale called the Mohs scale of hardness.
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Mohs Scale of Hardness © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Cleavage
•  Tendency to break along planes of weak
bonding
•  Produces flat, shiny surfaces
•  Described by resulting geometric shapes
– Number of planes
– Angles between adjacent planes
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Common Cleavage Direc/ons © 2011 Pearson Education, Inc.
Cleavage in Muscovite Mica © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Fracture
•  Absence of cleavage when a mineral is
broken
Conchoidal Fracture © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Specific gravity
•  Weight of a mineral / weight of an equal
volume of water
•  Most minerals are between 2 and 3.
•  Average value = 2.7
•  Galena-7.5
•  24 K gold- 20
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Crystal Shape or Habit © 2011 Pearson Education, Inc.
Physical Proper/es of Minerals •  Other properties:
•  Magnetism
•  Reaction to hydrochloric acid
•  Malleability
•  Double refraction
•  Taste
•  Smell
•  Elasticity
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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 Con/nental Crust © 2011 Pearson Education, Inc.
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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Mineral Groups •  Joining silicate structures
•  Single tetrahedra are linked together to form
various structures including:
– Isolated tetrahedra
– Ring structures
– Single- and double-chain structures
– Sheet or layered structures
– Complex three-dimensional structures
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Los Silicatos •  SiO4, Si es un ion pequeño con carga posi:va que cuadra muy bien dentro de los iones grandes con carga nega:va de oxigeno. O2O2- Si4+ O2O2-
•  Forman un tetraedro de silicio con carga de nega:vo 4 (-­‐4). Composi/on of Minerals Si (14)- 2, 8, 4
O (8)- 2, 6
2, 6 OO- Si OO-
=
SiO44-
•  Para formar una carga eléctrica neutral un tetraedro de silicio :ene que adquirir cuatro cargas posi:vas. •  Iones posi:vos se pueden unir al tetraedro o tetraedros adyacentes pueden compar:r sus oxígenos. •  Existen 5 grupos principales de estructuras cristalinas de silicio: –  Tetraedros independientes –  Cadenas simples –  Cadenas dobles –  Capas de tetraedros –  Estructuras tridimensionales de tetraedros Tetraedros independientes •  Los tetraedros independientes están unidos por un ion posi:vo y no comparten sus oxígenos. No :ene clivaje. •  Ej. Olivina Cadenas simples •  Cada tetraedro comparte dos oxígenos restando una carga de (-­‐2). Como la unión dentro de cada cadena es fuerte y la unión entre cadenas mas débil; estos minerales :enden a tener un (1) clivaje. •  Ej. piroxeno Cadenas dobles •  Una cadena doble se forma cuando tetraedros adyacentes comparten dos oxígenos y un tercer oxigeno es compar:do con otra cadena de tetraedros (2 clivajes) •  Ej. hornablenda Capas de tetraedros • 
Los tres oxígenos en la base del tetraedro son compar:dos. El cuarto oxigeno esta libre para unirse a un ion de carga posi:va (1 clivaje). •  Ej. Mica (bio:ta, moscovita) Estructuras tridimensionales de tetraedros •  Cuando todos los oxígenos son compar:dos con tetraedros adyacentes resulta en una estructura tridimensional. (2 ó 0) •  Ej. The Light Silicates •  Or nonferromagnesian. Generally light in color and specific gravity of about 2.7 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 © 2011 Pearson Education, Inc.
Mineral Groups •  Common silicate minerals
•  Light silicates: quartz
– Only common silicate composed entirely of
oxygen and silicon
– Hard and resistant to weathering
– Conchoidal fracture
– Often forms hexagonal crystals
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© 2011 Pearson Education, Inc.
Mineral Groups •  Common silicate minerals
•  Light silicates: muscovite
– Common member of the mica family
– Excellent cleavage in one direction
– Produces the “glimmering” brilliance often seen
in beach sand
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© 2011 Pearson Education, Inc.
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.
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The Dark Silicates •  Or ferromagnesian, contains ions of iron=ferro and/or magnesium. Because that content they are dark in color and have a greater specific gravity. © 2011 Pearson Education, Inc.
Mineral Groups •  Common silicate minerals
•  Dark silicates: olivine group
– High temperature Fe–Mg silicates
– Individual tetrahedra are linked together by Fe
and Mg ions.
– Forms small, rounded crystals with no cleavage
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Mineral Groups •  Common silicate minerals
•  Dark silicates: pyroxene group
– Single-chain structures involving iron and
magnesium
– Two distinctive cleavages at nearly 90 degrees
– Augite is the most common mineral in the
pyroxene group.
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Mineral Groups •  Common silicate minerals
•  Dark silicates: amphibole group
– Double-chain structures involving a variety of
ions
– Two perfect cleavages exhibiting angles of 124
and 56 degrees
– Hornblende is the most common mineral in the
amphibole group.
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Cleavage Angles for Augite and Hornblende © 2011 Pearson Education, Inc.
Mineral Groups •  Important nonsilicate 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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© 2011 Pearson Education, Inc.
Mineral Groups •  Important nonsilicate minerals
•  Carbonates
– Primary constituents in limestone and dolostone
– Calcite (CaCO3) and dolomite CaMg(CO3)2 are
the two most important carbonate minerals.
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Mineral Groups •  Important nonsilicate minerals
•  Many nonsilicate 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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Halite © 2011 Pearson Education, Inc.
Magne/te and Hema/te Are Both Iron Oxides © 2011 Pearson Education, Inc.
End of Chapter 3 © 2011 Pearson Education, Inc.