Rocks

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Chapter 4

• Rocks

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4.1 The Rock Cycle

• What is a rock?
• A mixture of minerals, mineraloids, glass, or
  organic matter
• The Rock Cycle
• Refer to figure 4-2
• Describes how one rock type can become another
  through different Earth processes

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4.2 Igneous Rocks

• Origin of Igneous Rocks
• Formed from the cooling of magma or lava
• Magma
• About 1400 degrees Celsius at 60-200km below
  Earths surface
• Rocks are under great pressure from above rocks
• Heat rises from the Earths interior

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4.2 Continued

• Heat and pressure has to be just right to melt
  the rocks
• Magma is less dense than the surrounding rock
• Magma is forced upward towards Earths surface
• Magma eventually reaches Earths surface and is
  now called lava

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4.2 Continued

• Two types of Igneous rocks
• Intrusive rocks
• As the magma cools deep below the Earths surface
  the atoms of minerals rearrange and form new
  crystals called mineral grains
• Have large mineral grains
• Are uncovered after many kms of rock have been
  eroded or pushed up

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4.2 Continued

• Extrusive rocks
• Formed from lava cooling at or just beneath the
  Earths surface
• Tend to have small mineral grains due to the
  rapid cooling
• Lava cools rapidly because of the air and
  moisture
• Pockets of air can become trapped leaving holes
  in the rock

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4.2 Continued

• Classification of Igneous Rocks
• Based on type of magma or lava the rock is formed
  from
• Three types of Magma or Lava
• (table 4-1)

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4.2 Continued

• Basaltic
• Dense, heavy, dark-colored
• Formed from Basaltic magma or lava
• Intrusive
• Gabbro
• Extrusive
• Basalt
• Scoria

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4.2 Continued

• Granitic
• Light-colored, lower density than Basaltic
• Intrusive
• Granite
• Extrusive
• Rhyolite
• Pumice
• Obsidian

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4.2 Continued

• Andesitic rocks
• Have mineral composition between Granitic and
  Basaltic rocks
• Intrusive
• Diorite
• Extrusive
• Andesite

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4.2 Continued

• Capable of learning
• Origin
• Formation
• Composition
• Igneous rocks are the most abundant type on Earth

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4.3 Metamorphic Rocks

• Origin of Metamorphic Rocks
• Rocks form from the pressure and heat of the
  Earth
• Rocks that undergo a change in composition
• Igneous, sedimentary, or other metamorphic rocks
  can form new metamorphic rocks

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4.3 Continued

• Heat and Pressure
• Together usually causes metamorphic rocks to form
• If only pressure is present
• Mineral grains are flattened
• Atoms of minerals are exchanged with other
  minerals
• Amount of pressure applied determines the type of
  rock formed

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4.3 Continued

• Classification of Metamorphic Rocks
• Based on texture of rocks
• Foliated Rocks
• Mineral grains are flattened and lined up in
  parallel bands
• Examples
• Slate formed from sedimentary shale
• Gneiss formed from igneous granite

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4.3 Continued

• Nonfoliated Rocks
• No banding is formed from mineral bands
• Mineral bands can change, grow or rearrange
• Examples
• Quartzite formed from sedimentary sandstone
• Marble formed from sedimentary limestone

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4.4 Sedimentary Rocks

• Origin of Sedimentary Rocks
• Begins with the erosion or weathering of igneous,
  metamorphic or other sedimentary rocks
• Eroded or weathered rock pieces are called
  sediments
• Formed from sediments being pressed together
• Cementing of sediments caused by evaporating
  solutions

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4.4 Continued

• Sediments loose materials transported by the
  wind, water, ice or gravity
• Examples rock fragments, mineral grains, bits
  of plant and/or animal remains
• Weathering process that breaks rocks into
  smaller pieces
• Pieces are classified by size
• Refer to table 4-2
• Erosion movement of weathered materials

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4.4 Continued

• Processes of Sedimentary rock formation
• Compaction
• Eroded particles are deposited
• Layers of sediment are formed
• Pressure of top layers causes lower layers to
  stick together
• Only works with small particles

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4.4 Continued

• Cementation
• Only works with large particles (sand, pebbles)
• Water moves through soil and rocks dissolving
  minerals
• Water and dissolved minerals move through spaces
  between large particles
• Dissolved minerals are deposited around large
  particles
• Large particles begin to stick together

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4.4 Continued

• Sedimentary rock layers
• Sedimentary rocks usually form in layers
• Older layers are deep young layers on top
• Layers can be disturbed by Earth processes
• Classification of Sedimentary Rocks
• Based on composition and the process that formed
  them

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4.4 Continued

• Three types of Sedimentary rocks
• Detrital Sedimentary Rocks
• Composed of other rock fragments
• Can be compacted or cemented together
• Said to have clastic texture broken texture
• Examples large sediment particle rocks
• Conglomerate sediments are well rounded
• Breccia sediments are sharp and angled

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4.4 Continued

• Examples small sediment particle rocks
• Sandstone sand grains that are cemented or
  compacted
• Shale clay particles compacted

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4.4 Continued

• Chemical Sedimentary Rocks
• Form when minerals are precipitated from a
  solution or are left behind when a solution
  evaportates
• Examples
• Limestone formed from calcite crystals
  precipitating and growing together
• Rock salt halite and other minerals left behind
  after evaporation of salt water

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4.4 Continued

• Organic Sedimentary Rocks
• Formed from the remains of once-living organisms
• Example
• Fossil-rich limestone limestone with numerous
  fossils
• Useful organic sedimentary rocks
• Chalk formed from small pieces of shells in
  limestone Coal formed from dead plants being
  buried in swamps

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4.4 Continued

• Another Look at the Rock Cycle
• There is no beginning or end
• Rocks are always changing from one type to
  another

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4.5 Burning Waste Coal

• Cogeneration from Waste Coal
• Used to generate electricity and energy
• Waste coal
• Poor quality coal piled near old coal mines
• High sulfur content causes acid runoff

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4.5 Continued

• How do we get rid of it?
• Coal is burnt with limestone, which helps absorb
  sulfur dioxide
• Burned mixture is transported back to the
  original pile
• Burned mixture is alkaline and helps neutralize
  the acid runoff

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4.5 Continued

• Cogeneration
• Waste coal can be burnt to create electricity
• Low pressure steam can be used as a heat source
• Both the electricity and the thermal energy must
  be used by the plant creating it to be considered
  a process of cogeneration