Minerals: Building Blocks of Rocks

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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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What is a mineral?
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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
  (angstrom is 10-10 m).
• At the center of an atom is a nucleus which
  contains most of the mass of the atom.
• Protons (positive charge)
• Neutrons (no charge -- neutral)
• Electrons (negative charge) orbit the nucleus.

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Atoms

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

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Periodic Table
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Atoms

• Atomic Number Number of protons in an atom
• Atomic Mass Sum of the masses of the protons
  and neutrons in an atom.
• 12C carbon-12 (6 protons and 6 neutrons)
• 13C carbon-13 (6 protons and 7 neutrons)
• 14C carbon-14 (6 protons and 8 neutrons)
• Atoms with the same number of protons and
  different numbers of neutrons are called isotopes.

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Atomic structure
Nucleus protons, neutrons

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

Fig. 3.2
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C-12
Fig. 3.2
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Electron Cloud
Fig. 3.2
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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

Atoms are MOST STABLE when their outer electron
shell is filled.
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Bonding

• Atoms join with other atoms to try to fill their
  outer shells.
• Two types of bonds
• Ionic bond Formed by the electrical attraction
  of ions of opposite charge. 90 of minerals are
  formed through ionic bonds.
• Covalent bonds Formed by sharing electrons.
  Metallic bonds are one type of covalent bond.
  Diamonds.

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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.
• 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. 3.4
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Halite
Fig. 3.4
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Atomic Structure of Sodium Chloride (Halite)
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Halite close-up
Fig. 3.6
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Electron Sharing in Diamond
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Carbon Tetrahedron of Diamond
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Network of Carbon Tetrahedra
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Electron Sharing in Diamond
Fig. 3.5
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Crystals

• Crystal Ordered three-dimensional arrays of
  atoms in which the basic arrangement is repeated
  in all directions.

Fig. 3.8
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How do minerals form?

• Crystallization The growth of a solid from a
  gas or liquid whose constituent atoms come
  together in the proper chemical proportions and
  crystalline arrangement.
• When do minerals form?
• Crystallization from a magma
• Crystallization from a pre-existing solid phase
• Precipitation from solution (halite, evaporation)

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Crystals

• Crystal face Boundaries of crystals. Natural
  flat (planar) surfaces. External expression of a
  minerals internal atomic structure.
• Perfect crystal Crystal for which crystal faces
  are easily observed. Requires crystallization
  under special conditions (e.g., enough room to
  grow).

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Quartz Geode
Large space allows larger crystals
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Ionic Radii Determine Packing Geometry
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Graphite
Atomic Structure Crystal Form
After Fig. 3.11
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Diamond
Atomic Structure Crystal Form
After Fig. 3.11
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Polymorphs

• Minerals with the same chemical composition but
  different structure.
• For example
• diamond (3.5 g/cm3) and graphite (2.1 g/cm3)
• andalusite, kyanite, and sillimanite

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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.
• Groups
• Silicates. Si, O and other elements. Most
  abundant mineral group in the Earths crust
  (gt75).
• Carbonates. Ca, Mg and CO3
• Halides or Salts. NaCl
• Sulfides. Sulfide anion (S2-) and a metallic
  cation.
• Oxides. O and a metallic cation.

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Chemical classes
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Important mineral groups
Name Important constituents
Silicates 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 Sulfides Fe, Cu, Zn,
Ni Oxides Fe, Al
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Silica-oxygen tetrahedra

• Building blocks of silicate minerals
• 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. 3.11
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Olivine
Isolated Tetrahedra Silcate (example olivine,
(Mg,Fe)2SiO4)
Fig. 3.11
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Some Silicate Minerals
Mica
Feldspar
Olivine
Pyroxene
Quartz
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Oxides
Hematite, Fe2O3
Corundum, Al2O3
Magnetite, Fe(II)Fe(III)2O4
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Sulfates
Galena, PbS
Gypsum, CaSO42H2O
Pyrite, FeS2
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Carbonates
Dolomite, CaMg(CO3)2
Calcite, CaCO3
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Atomic Structure of Calcium Carbonate(Calcite)
Fig. 3.12
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Important Crustal Minerals

• Feldspar (60 of crust) NaAlSi3O8, CaAl2Si2O8
• Quartz (12 of crust) SiO2

Oxygen (O) 46.3 Silicon (Si) 28.2 Aluminum
(Al) 8.2 Iron (Fe) 5.6 Calcium
(Ca) 4.1 Sodium (Na) 2.4 Potassium
(K) 2.1 Magnesium (Mg) 2.3 Titanium
(Ti) 0.5 Nickel (Ni) trace All others trace
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Important Mantle Minerals

• Olivine (60 of upper mantle) (Mg,Fe)2SiO4
• Clinopyroxene (25 of upper mantle)
  Ca(Mg,Fe)Si2O6
• Orthopyroxene (10 of upper mantle) (Mg,Fe)SiO3
• Garnet (5 of upper mantle) X2Y3Si3O12, where
  X Ca, Fe, Mg, or Mn, and Y Al, Cr, or Fe

Oxygen (O) 29.5 Silicon (Si) 15.2 Aluminum
(Al) 1.1 Iron (Fe) 34.6 Calcium
(Ca) 1.1 Sodium (Na) 0.6 Potassium
(K) 0.1 Magnesium (Mg) 12.7 Titanium
(Ti) 0.1 Nickel (Ni) 2.4 All others 2.7
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Solid Solution

• Like solutions, minerals can have a range of
  compositions.
• Continuous range of mineral compositions is
  called solid solution.
• The range in composition is created because at a
  single location in the crystal, several elements
  are permitted.
• Example
• Olivine (Mg,Fe)2SiO4
• Elements between parentheses indicate a
  substitution
• End members Fosterite (Mg2SiO4) and Fayalite
  (Fe2SiO4).

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IonicRadiusandCharge
Fig. 3.7
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Mineral identification
In hand specimen

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

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Hardness

• A measure of the ease with which the surface of a
  mineral can be scratched.

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Cleavage

• The tendency of a crystal to break along flat,
  planar surfaces.

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Cleavage
Atomic Structure of Micas
Fig. 3.17
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Sheety Cleavage of Mica
Fig. 3.17
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Rhomboidal Cleavage of Calcite
Fig. 3.18
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Luster

• The way in which a mineral reflects light.

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Streak

• The color of a fine deposit of mineral dust on an
  abrasive surface, such as a tile of unglazed
  porcelain (streak plate).

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Hematite
Streak
Fig. 3.20
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Calcite passes the acid test
Fig. 3.16