GEOS 251/S2006

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GEOS 251/S2006

• Minerals Building Blocks of Rocks

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Mineral

• A naturally occurring, inorganic solid with an
  ordered internal structure and a narrow range of
  chemical composition

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Fig. 2.1
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Rock

• A naturally occurring consolidated mixture of
  minerals or mineral-like substances

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Atoms

• A rigid sphere about 1 angstrom (Å) in diameter
  -- an angstrom is 10-10 m
• At the center of an atom is a nucleus which
  contains most of the mass of the atom
• Protons with a positive charge
• Neutrons with no charge -- neutral
• Quarks and other interesting things

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Atoms

• Electrons (E) negative charge, very little mass
• Protons (Z) positive charge, mass 1832 times
  greater than electron
• Neutrons (N) no electric charge, mass 1833 times
  greater than electron

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Abundance of the elements (wt. )

• Crust Whole Earth
• Oxygen 46.3 29.5
• Silicon 28.2 15.2
• Aluminum 8.2 1.1
• Iron 5.6 34.6
• Calcium 4.1 1.1
• Sodium 2.4 0.6
• Potassium 2.1 0.1
• Magnesium 2.3 12.7
• Titanium 0.5 0.1
• Nickel trace 2.4
• All others trace 2.7

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Atomic structure
Nucleus protons, neutrons

• Electrons orbit
• around the
• nucleus in
• discrete shells.

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Fig. 2.2a
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Energy-level shell the space occupied by
electrons of a particular energy level

• First level (K) 2 electrons
• Second level (L) 8 electrons
• Third level (M) 18 electrons
• Fourth level (N) 32 electrons

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L
K
Fig. 2.2b
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L
K
Fig. 2.2c
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Fig. 2.3a
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Fig. 2.3b
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Fig. 2.3c
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Atomic structure

• Chemical characteristics of elements determined
  largely by number of protons
• of protons atomic number (A)
• of neutrons (N) A atomic weight (Z)

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Ion
An electrically charged particle composed of an
atom that has either lost or gained electron(s)
to or from another atom.
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Ions
When an atom loses or gains an electron it is
called an ion. Positively charged ions (loss of
electron) are called cations. Negatively charged
ions (gain of electron) are called anions.
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Important ions in minerals
anions charge cations charge
Si 4 K 1 Ca 2 Na 1 Al 3 Mg 2 Fe 2 or 3
O -2
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Ionic Attraction Forms NaCl (Halite)
Fig. 2.4c
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Electron Sharing in Diamond
Fig. 2.5
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Chemical Symbols

• Oxygen O Magnesium Mg
• Silicon Si Iron Fe
• Aluminum Al Sodium Na
• Potassium K Calcium Ca
• Carbon C Titanium Ti
• Hydrogen H Argon Ar
• Uranium U Zirconium Zr
• Strontium Sr Lead Pb

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Periodic Table of Elements
Fig. 2.6
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(H)
(Na)
P Proton N Neutron
Fig. 2.7
(Mg2)
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(O2-)
P Proton N Neutron
(Cl-)
Fig. 2.7
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Carbon Tetrahedron of Diamond
Fig. 2.8a
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Network of Carbon Tetrahedra
Fig. 2.8b
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Atomic Structure of Sodium Chloride (Halite)
Fig. 2.9
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Galena
Fig. 2.10b
Chip Clark
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Perfect Crystals
Halite (cube)
Quartz (hexagonal)
Fig. 2.11
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Halite (Cubic) and Quartz (Hexagonal)
Ed Degginger Bruce Coleman
Breck P. Kent
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Quartz Geode
Large space allows larger crystals
Fig. 2.12
Chip Clark
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Ionic Radii Determine Packing Geometry
Fig. 2.13
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Ionic Radius and Charge
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Graphite
Atomic Structure Crystal Form
Ken Lucas, Visuals Unlimited
Fig. 2.15a
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Diamond
Atomic Structure Crystal Form
E.R. Degginger, Photo Researchers
Fig. 2.15b
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Polymorphs
Minerals with the same chemical composition but
different structure. e.g., diamond and
graphite andalusite, kyanite, and sillimanite
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Polymorphs of Carbon
P.L. Kresan
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Minerals lots and lots of em

• There are some 3,500 recognized minerals found on
  Earth.
• However,
• For our purpose, we can focus on about a dozen.
• Silicates - Si, O and other elements, the most
  abundant mineral group in the Earths crust
• Carbonates - Ca, Mg and CO3
• Salts - NaCl

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Silica-oxygen tetrahedra

• Four oxygens surrounding a silicon ion.
• These tetrahedra combine to make the framework of
  the silicates.
• Different combinations produce different
  structures.

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Silicate IonSiO4 4
Fig. 2.16a
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Fig. 2.16b
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Olivine
Chip Clark
Isolated Tetrahedra Silcate (example olivine)
Fig. 2.17a
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Fig. 2.17
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Sheet Silicate (example mica)
Fig. 2.17d
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Framework Silicate (example quartz)
Fig. 2.18
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Some Silicate Minerals
Mica
Feldspar
Olivine
Pyroxene
Quartz
Chip Clark
Fig. 2.19
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Mafic Silicates
Olivine
Pyroxene
Felsic Silicates
Quartz
Feldspar
Chip Clark
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Important mineral groups
Name Important constituents
(other than O)
Olivine Si, Fe, Mg Pyroxene Si, Fe, Mg,
Ca Amphibole Si, Ca, Mg, Fe, Na, K Micas Si, Al,
K, Fe, Mg Feldspars Si, Al, Ca, Na,
K Carbonates C, Ca, Mg Evaporites K, Cl, Ca, S
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Some Nonsilicate Minerals
Spinel
Halite
Gypsum
Hematite
Galena
Calcite
Pyrite
Chip Clark
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Oxides
Hematite
Magnetite
Corundum
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Sulphates
Galena
Gypsum
Pyrite
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Carbonates
Dolomite
Calcite
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Atomic Structure of Calcium Carbonate (Calicite)
Fig. 2.21a
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Atomic Structure of Calcium Carbonate(Calcite)

Fig. 2.21b
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Important minerals
Quartz SiO2 Calcite CaCO3 Biotite Olivine (Mg,Fe)
2SiO4 Plagioclase feldspar K-feldspar
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Mineral formation

• Crystallization from a magma
• Crystal growth in the solid state
• Precipitation from solution

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Mineral identification

• Color
• Crystal form
• Hardness
• Cleavage
• Density
• Streak

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Calcite passes the acid test
Fig. 2.22
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Aldo Tutino Art Resource
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Atomic Structure of Micas
Fig. 2.23
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Sheety Cleavage of Mica
Fig. 2.23
Chip Clark
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Rhomboidal Cleavage of Calcite
Fig. 2.24
Chip Clark
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Comparison of Cleavage and Crystal Faces
Pyroxene
Amphibole
Fig. 2.25
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Hematite
Streak
Fig. 2.26
Brent P. Kent
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Chrysotile (a Form of Asbestos)
Runk/Schoenberger/Grant Heilman Photography