Earth Materials--Rocks and Minerals

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Earth Materials--Rocks and Minerals

• CHAPTER 2

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Minerals and Rocks

• Definition of a mineral
• Naturally occurring
• Inorganic
• Solid
• Definite chemical composition (or range)
• Orderly internal crystal structure

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Mineral Importance

• Economic
• Conditions of environment
• Definition of a Rock
• An aggregate or one or more minerals

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Physical Properties of Minerals

• Color - the color of the mineral as it appears to
  the naked eye in reflected light.
• Luster - the character of the light reflected
  from the mineral. A mineral may have a metallic
  luster or a non-metallic luster.
• Hardness - the resistance of a mineral to
  scratching. Hardness is measured on a scale of 1
  - 10 called Mohs Hardness Scale. Hardness of
  minerals can also be compared to common objects
  (fingernail, copper penny, nail, glass).

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Physical Properties of Minerals

• Cleavage - the tendency of a mineral to break
  along flat surfaces related to planes of weakness
  in its crystal structure.
• Fracture - irregular breakage not related to
  planes of weakness in the mineral.
• Magnetism.
• Reaction to acid - The carbonate minerals react
  with diluted hydrochloric acid (HCl) by
  effervescing or fizzing, producing bubbles of
  carbon dioxide gas.

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Silicate Minerals

• Silicate Minerals have Si and O in their
  formulas
• Feldspars (60 of Earth's crust) plagioclase and
  orthoclase varieties
• Quartz
• Micas muscovite and biotite
• Hornblende (amphibole)
• Pyroxene (augite)
• Olivine
• Clay minerals

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Minerals

• Nonsilicate minerals (8 of Earth's crust)
• Carbonates (with CO2) dolomite, calcite,
  aragonite
• Oxides (with O) hematite, goethite, limonite
• Halides (with Cl) halite, sylvite
• Sulfates (with SO4) gypsum, anhydrite
• Sulfides (with S) pyrite, galena
• Native elements gold, copper, silver

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Figure 2-12 Geologic processes act continuously
on Earth to change one type of rock into another.
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Igneous Rocks

• Igneous Rocks (90 by volume of Earth's crust)
• Cooling history of magma or lava is reflected in
  the texture
• intrusive (plutons, dikes, sills) phaneritic
  (coarse) texture
• extrusive (lava flows, ash falls) aphanitic
  (fine) texture
• two-stage (slow cooling followed by more rapid
  cooling) porphyritic texture
• Very rapid cooling may result in glassy texture

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Igneous textures
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Mineral composition, texture, and other
properties of common igneous rocks.
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Igneous Rocks

• Crystallization of magma
• first-formed minerals have more perfect shapes
• Bowens reaction series helps us understand order
  of mineral formation
• continuous reaction series feldspar composition
  changes
• discontinuous reaction series iron-rich silicate
  minerals reacts with liquid

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A depiction of Bowens Reaction Series. Note that
the earliest minerals to crystallize are olivine
and calcium-rich plagioglase. As crystallization
proceeds, each mineral reacts with the melt to
form the mineral beneath it.
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Volcanic Activity

• Volcanism (volcanic activity)
• Explosive- High Water, High Silica, High
  Viscosity (example andesitic)
• Quiet-Low viscosity, Low Silica, Low water
  content (example basalt)

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An andesitic melt resulting from fractional
crystallization of a basaltic magma.
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Sedimentary Rocks

• Sediment loose particulate material (clay,
  sand, gravel, etc.)
• Derivation by weathering
• decomposition (chemical)
• disintegration (physical)
• Sediment becomes sedimentary rock through
  lithification, which involves
• Compaction
• Cementation
• Recrystallization (of carbonate sediment)

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A conceptual diagram showing how the weathering
of granitic rock yields quartz grains for quartz
sandstone, clay for shale, and calcium for
limestone.
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Types of Sedimentary Rocks

• Clastic (also called terrigenous or detrital)
• Conglomerate or Breccia
• Sandstone
• Siltstone
• Shale or Claystone

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Clastic Sedimentary Rocks
Shale
Sandstone
Conglomerate
Breccia
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Chemical/Biogenic Sedimentary Rocks

• Chemical/biochemical
• Evaporites
• Carbonate sedimentary rocks (limestones and
  dolostone)
• Siliceous sedimentary rocks
• Organic (coals)

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Carbonate (calcite)
Halite
Coal
Chert
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Metamorphic Rocks

• Metamorphic means "changed form"
• Agents of metamorphism
• Heat
• Pressure
• Chemically active fluids

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Types of Metamorphism

• Contact metamorphism -alteration of rock by heat
  adjacent to lava or magma
• Regional metamorphism - alteration of rock over a
  large area by heat and pressure due to deep
  burial or tectonic pressure

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Changes in minerals that will develop during the
progressive metamorphism of shale
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Texture of Metamorphic Rocks

• Foliation - laminated structure in a metamorphic
  rock resulting from the alignment of sheet-like
  minerals (usually micas).
• Non-foliated or granular metamorphic rocks are
  those which are composed of equidimensional
  grains such as quartz or calcite. There is no
  preferred orientation. The grains form a mosaic.

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Foliated Metamorphic Rocks

• The following are derived from the progressive
  metamorphism of shale
• Slate
• Phyllite
• Schist
• Gneiss (can also form from the metamorphism of
  granite)

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Foliated Metamorphic Rocks
Slate
Phyllite
Schist
Gneiss
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Non-foliated Metamorphic Rocks

• Marble parent rock is limestone or dolomite
• Quartzite parent rock is sandstone
• Hornfels parent rock is shale or siltstone
• Greenstone parent rock is basalt

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Non-foliated rocks
Marble
Quartzite