Chapter 3 Matter and Minerals

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Chapter 3 Matter and Minerals

• Minerals The Building Blocks of Rocks

Naturally occurring,
Inorganic,
Solid,
Orderly structure,
Definite Chemical Composition,
Definite characteristics
Rock less well defined. As defined by the
text, a rock is any naturally-occurring, solid
mass of mineral or mineral-like material.
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• Andradite Garnet one of several garnets

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• Most rocks are aggregates of different minerals,
  with the individual mineral grains retaining
  their original characteristics. A few rocks
  (limestone, marble, quartzite) can be composed of
  a single mineral.
• Because the mineral characteristics and
  arrangements affect the rock properties, we study
  the individual minerals first.
• Most important are the Rock-Forming Minerals,
  most of which are composed of silicon and oxygen
  (silicates) (slides 13 17).

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• Atom smallest unit of an element with all of
  the characteristics of that element.
• Atoms consist of a nucleus composed of protons
  and neutrons and one or more shells of orbiting
  electrons.

Periodic Table (p. 75) arranged by Atomic numbers
(s of protons). Atomic mass protons
neutrons. Electrons protons.
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• Atoms are neutrally charged. Number of electrons
  Number of protons.
• In the electron shells shell 1 carries 2
  electrons. Successive shell carry up to 8
  electrons. If outer-most shell has 8 elec-trons,
  the atom is a noble element (Helium, Neon,
  Argon, Krypton, Xenon, Radon). If there are
  spaces in the outer shell, then the atom may gain
  or lose 1 or more electrons.
• Ion an atom that has either gained or lost
  electrons.

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Ionic bond attraction of
opposite electrical charges.
Halite table salt NaCl
Anion Cation
Covalent bonds share some electrons between ions.
Metallic bonds share all electrons.
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• Molecule A group of ions (as a unit)
• Has unique properties.
• Held together by differing electrical charges or
  by the sharing of electrons between ions.
• Most minerals are compounds and most compounds
  are covalent.
• Major atmospheric gases are present as
  covalently-bonded molecules (O2, N2, H2, etc.).
• Minerals are classified by Anion group. Ex
  Halite is halide mineral.

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• Calcite Carbonate Wollastonite - Silicate

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• Isotope varieties of atoms, with one or more
  extra neutrons. Same atomic number, different
  atomic mass. Hydrogen has three forms Proteum,
  Deuterium, and Tritium. Tritium is radioactive,
  with a half-life of about 12.5 years.

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• Nature of ionic bonds affect the Physical
  Properties of Minerals (pp. 83-87)
• Color may not be reliable due to impurities
• Impurities may cause color variations.
• Luster appearance of reflected light from
  surface. Ex Metallic vs. Non-metallic
• Crystal form good crystals may be rare, as
  crystals must compete for space while growing.
  Crystals have planar surfaces, sharp corners,
  straight edges.
• Streak color of powdered mineral on unglazed
  ceramic tile.

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• Hardness Resistance to scratching, does not
  refer to susceptibility to breakage
• Cleavage tendency to break along weak bonds,
  leaving a smooth surface. Cleavage planes are
  parallel and a particular mineral has a
  characteristic of cleavages, e.g., mica has one
  direction of cleavage.
• Fracture tendency to break along irregular
  surfaces
• Specific gravity density, comparison with equal
  volume of water. Common minerals 2.5 to 3
  gm/cm3

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• Cleavage examples
• Mica 1 direction of perfect cleavage
• Feldspars 2 directions of good cleavage
• Galena, Halite 3 directions of good cleavage at
  900 angles (forms cubes)
• Calcite 3 directions of cleavage, forms rhombs
  (3-dimensional forms without 900 angles).
• Fluorite 4 directions of good cleavage, forms
  octahedral diamonds
• No cleavage Quartz, garnet, pyrite, olivine,
  tourmaline.

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Heavy minerals specific gravity gt quartz
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• Mohs Scale of Hardness (pg. 86) relative
  hard-nesses of common minerals and other
  materials

Other properties (p. 46), taste, feel, reaction
to acids, etc..
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We learn to study the minerals individually
first, then as components of rocks. Silicates
are the most important of the rock forming
minerals, 95 of crust, 33 of all minerals.
These minerals are built around the silica
tetrahedra (Fig. 3.27, pg. 90), composed of one
silicon cation and four oxygen anions. The
tetrahedra link together in individual
tetrahedra, single chains, double chains, sheet
structures, and 3-dimensional frameworks (Fig.
3.29, pg. 92).
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Olivine Pyroxene Amphibole Micas Feldspar Quart
z
Silicate Structures Oxygen to Silicon
ratios Isolated tetrahedra 41 Single
chain 31 Three dimensional
21 Structural complexity increases (see p. 92)
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Order of crystallization of silicate minerals.
Minerals at top weather more easily
Hotter Crystallization temps Darker More Dense
Hotter Cooler
Gabbro Diorite Granite
Cooler Crystallization temps Lighter Less
Dense
Minerals at bottom are more resistant to
weathering
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Dark Rock-Forming Silicate Minerals (p. 52)
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Light Rock-Forming Silicate minerals (p. 53)
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What is this black crystal? Identification tips.
Pyroxene two angles of cleavage at 900,
crystals usually short, blocky. Amphibole two
angles of cleavage at approx. 600 and 1200,
crystals usually long, slender. Tourmaline no
cleavage, crystals may show triangular
cross-section. Present in some Gwinnett
quartzites gneisses (metamorphics).
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• Most important non-silicate Rock-Forming
  minerals are carbonates, i.e., minerals with
  carbonate ion (CO3)-2 , as in calcite (CaCO3),
  found in limestone and dolomite CaMg(CO3)2,
  found in dolostone. Metamorphic marble may
  contain both.
• Other mineral groups are primarily important as
  resources, e.g., oxides, halides, phosphates,
  sulfates, sulfides, others page 58, Table 2.4

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• Newton County rocks are exclusively metamorphic
  except for diabase dikes, granites, and small
  pegmatites (irregular igneous bodies with large
  crystals).
• Light-colored rocks that show mineral banding
  Gneiss.

Rocks dominated by micas Schist. Black rock
with small aligned crystals Amphibolite.
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• What is this translucent/transparent light green
  mineral?
• Olivine No cleavage, harder than a steel nail.
• Fluorite 4 directions of cleavage, hardness of
  4 (softer than nail).
• Epidote present in Piedmont Province gneisses,
  as vein fracture fillings or replacements of
  some feldspars.
• What are these reddish-brown lumps? Probably
  garnets.

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• Micas you may see in Newton County
• Muscovite light brown. Large flakes, probably
  igneous rocks, small flakes, probably metamorphic
  rocks.
• Biotite black, primarily occurs as layers in
  gneisses (rocks that look like granite, but show
  mineral banding layers).
• Chlorite dark green or dark bluish-green,
  present as dark schists, often with pyrite
  crystals.