MINERALS: BUILDING BLOCKS OF ROCKS

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Chapter 3
MINERALS BUILDING BLOCKS OF ROCKS
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Matter and Its Composition

• Matter
• anything that has mass and occupies space
• exists as solids, liquids, gases, and plasma
• consists of elements and atoms
• Element
• a chemical substance
• composed of tiny particles called atoms

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Periodic table of the Elements
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Atoms

• Atoms are the smallest units of matter
• that retain the characteristics of the element
• Atoms have
• a compact nucleus containing
• protons particles with a positive electrical
  charge
• neutrons electrically neutral particles
• particles outside the nucleus
• electrons negatively charged particles

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MODEL OF THE ATOM
Electron Orbits
Protons Red. Positive Charge.
Neutrons Green. Neutral Charge.
Nucleus
Electrons Tan. Negative Charge.
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Atoms

• Atomic number
• the number of protons
• Atomic mass number
• number of protons number of neutrons
• The number of neutrons in nucleus of an element
  may vary

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Isotopes

• Isotopes
• the different forms of an elements atoms
• with varying numbers of neutrons
• Different isotopes of the same element
• have different atomic mass numbers
• Isotopes are important in radiometric dating

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Carbon Isotopes

• Three isotopes of carbon (all with 6 protons)
• 6 neutrons Carbon 12 (12C)

• 7 neutrons Carbon 13 (13C)

• 8 neutrons Carbon 14 (14C)

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Electrons and Shells

• Electrons lie outside the nucleus in one or more
  shells
• The outermost shells are involved
• in chemical bonding
• and contain up to 8 electrons
• Noble gas configuration of 8 electrons
• or 2 for helium
• have complete outer shells
• and are stable
• Other atoms attain
• a noble gas configuration
• in the process of bonding

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Bonding and Compounds

• Bonding
• the process whereby atoms join to other atoms
• Compound
• a neutral substance resulting from the bonding
• of two or more elements
• Oxygen gas (O2) is an element
• Ice (H2O) is a compound
• made up of hydrogen and oxygen atoms
• Most minerals are compounds

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Ionic Bonding

• One way for atoms to attain the noble gas
  configuration
• is by transferring electrons, producing ions
• Ion
• an atom that has gained or lost one or more
  electrons
• and thus has a negative or positive charge
• Ionic bonding
• attraction between two ions of opposite charge

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Ionic Bonding

• Bonding and Compounds
• Ionic Bonds - Ionic bonds transfer ions, with
  opposite electrical charges attracting one another

• Halite is a compound formed by the bonding of
  sodium atoms to chlorine atoms.

Fig. 3.5, p. 65
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Covalent Bonding

• Another way for atoms
• to attain the noble gas configuration
• is by sharing electrons

• Covalent bonding
• results from sharing electrons

shared electrons
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Covalent Bonding Diamond and Graphite

• Bonding and Compounds
• Covalent Bonds - Covalent bonds atoms share
  electrons.

Fig. 3.6, p. 66
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Other Types of Chemical Bonds

• Metallic Bonds
• Metallic bonds result from extreme electron
  sharing.
• The nucleus of metallic atoms are not strongly
  attracted to their valence electrons thus
  adjacent nuclei may temporarily capture valence
  electrons from neighboring atoms.
• Van der Waals bonds
• Van der Waals bonds are an extremely weak bond
  without available electrons to form an
  attraction.
• Vand der Waals bonds form due to an unequal
  distribution of electrons around and atom or
  molecule that results in an electrical dipole
  around the atom or molecule (example the water
  molecule).

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Minerals

• Geological definition of a mineral
• naturally occurring
• crystalline solid
• crystalline means that minerals
• have atoms arranged in specific 3-dimensional
  frameworks

• minerals have a narrowly defined chemical
  composition
• and characteristic physical properties such as
• density
• hardness
• color...

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MineralsThe Building Blocks of Rocks

• A minerals composition is shown by a chemical
  formula
• a shorthand way of indicating how many atoms of
  different kinds it contains

• Quartz molecules consist of 1 silicon atom and 2
  oxygen atoms

Quartz SiO2 Ratio 1 2

• Orthoclase molecules consists of 1 potassium, 1
  aluminum, 3 silicon, and 8 oxygen atoms

KAlSi3O8 1 1 3 8
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Native Elements

• A few minerals consist of only one element.
• They are not compounds.
• They are known as native elements.
• Examples

• Gold Au

• Diamond C

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Crystalline Solids

• By definition, minerals are crystalline solids
• with atoms arranged in a specific 3D framework
• If given enough room to grow freely,
• minerals form perfect crystals with
• planar surfaces, called crystal faces
• sharp corners
• straight edges

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Narrowly Defined Chemical Composition

• Some minerals have very specific compositions
• Examples halite (NaCl), quartz (SiO2)
• Other minerals have a range of compositions
• because one element can substitute for another
• if the atoms of the two elements have
• the same electrical charge
• and are about the same size
• Example olivine
• (Mg,Fe)2SiO4
• iron and magnesium substitution in any proportion

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Mineral Properties

• Mineral properties are controlled by
• Chemical composition
• Crystalline structure
• Mineral properties are particularly useful
• for mineral identification and include

• cleavage
• fracture
• hardness
• specific gravity

• color
• streak
• luster
• crystal form

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How Many Minerals Are There?

• More than 3500 minerals are known
• Only about 2 dozen are particularly common
• Many others are important resources
• Mineral groups
• minerals with the same negatively charged ion or
  ion group
• belong to the same mineral group
• Most minerals that make up rocks of the crust
• belong to the group called silicates

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Composition of continental crust
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Silicates

• Silicates are minerals containing silica
• Si and O
• These minerals make up perhaps 95 of Earths
  crust
• and account for about 1/3 of all known minerals
• The basic building block of silicates
• is the silica tetrahedron
• which consists of one silicon atom
• surrounded by four oxygen atoms

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The silica (SiO4)-4 tetrahedron
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Types of Silicates

• Silica tetrahedra can be
• isolated units bonded to other elements
• arranged in chains (single or double)
• arranged in sheets
• arranged in complex 3D networks

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Types of Silicates

• Ferromagnesian silicates
• contain iron (Fe), magnesium (Mg), or both
• Nonferromagnesian silicates
• do not contain iron or magnesium

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Ferromagnesian Silicates

• Common ferromagnesian silicates include

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Other Mineral Groups

• Carbonates
• minerals with carbonate ion (CO3)-2
• calcite (CaCO3),
• constituent of limestone
• dolomite CaMg(CO3)2,
• constituent of dolostone
• Sulfates (Gypsum and Anhydrite) Rock Gypsum
• Halites (Halite) Rock Salt
• Other mineral groups are important,
• but more as resources
• than as constituents of rocks

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Mineral Groups Recognized by Geologists

• Carbonate Minerals
• Carbonate minerals are found mostly in the
  sedimentary rocks limestone and dolostone.
• Carbonates are derived from the shells and hard
  parts of marine organisms or are precipitated
  from seawater as evaporites.

Fig. 3.11, p. 70 Fig. 3.14, p. 75
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Table 2-1, p. 21
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Rock-Forming Minerals

• Most rocks are solid aggregates
• of one or more minerals
• Hundreds of minerals occur in rocks,
• but only a few are common
• and are called rock-forming minerals
• Most rock-forming minerals are silicates,
• but carbonates, halides, and sulfates are also
  important
• Accessory minerals are present in small amounts
• and are ignored in classifying rocks (example
  pyrite)

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Rock-Forming Minerals

• How do rock-forming minerals differ from
  accessory minerals?

• A few minerals are common enough to be known as
  rock-forming minerals. Most of these are
  silicates.
• Accessory minerals can be ignored in this
  endeavor because they are present in minor
  quantities.

Table 3.3, p. 80
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Natural Resources and Reserves

• How does a resource differ from a reserve?
• A resource is any solid, liquid, or gaseous
  substance in rocks whose profitable extraction is
  potentially feasible. Many resources are
  concentrations of economically important
  minerals.
• A reserve is only that part of the resource base
  that can be extracted economically.

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Natural Resources and Reserves

• While the United States is dependent on imports
  for many mineral resources, Canada is more
  self-reliant.

Fig. 3.20, p. 81
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Natural Resources and Reserves

• What factors affect the status or a resource?

• Market price is the most obvious determinate of
  whether a commodity is classified as a resource
  or reserve
• Other factors include geographic location, labor
  costs, and developments in science and
  technology.

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END