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Rocks

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Rocks Chapter 10 – PowerPoint PPT presentation

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Title: Rocks


1
Rocks
  • Chapter 10

2
Rocks the Rock Cycle
  • Magma is the parent material for all rocks
  • There are 3 major types
  • Any type can be changed into any of the other
    types through a series of changes called the rock
    cycle

3
3 Major Rock Types
  • Three major types
  • Igneous magma cools hardens
  • Sedimentary sediment is deposited and hardens
    after being compressed cemented.
  • Metamorphic forces such as extreme heat and
    pressure and chemical processes change the form
    of existing rock.

4
The Rock CycleOverview
  • Hardened magma cools -gt igneous rock
  • Igneous rock breaks down into sediments -gt
    sedimentary rock
  • Sedimentary rock subjected to extreme
    heat/pressure -gt metamorphic rock
  • Metamorphic rock under extreme heat/pressure -gt
    melt into magma (start over)

5
The Rock Cycle (cont)
  • Rock does not always make it through entire cycle
  • Igneous rock not exposed to surface will never
    become sediment may go directly to metamorphic
  • Igneous and sedimentary may melt directly into
    magma
  • All 3 types may form sediments when exposed

6
The Rock Cycle
7
Igneous Rock
  • Two types classified by where magma cools
  • intrusive cool deep below crust
  • May intrude into other rock layers
  • Cools slowly
  • extrusive lava cooling on surface
  • Cools rapidly

8
Igneous Rock (cont)
  • Texture determined by rate of cooling
  • Intrusive cools slowly
  • Course-grained texture
  • Ex granite
  • Extrusive cools rapidly
  • Little time for crystal formation
  • Fine-grained texture
  • Ex basalt

9
Igneous Rock (cont)
  • Some extrusive rock cools slowly at first then
    more quickly as it nears the surface
  • Produces both large and small crystals
  • Porphyry
  • Extremely rapid cooling produces rock without
    crystals
  • Gases escaping during rapid cooling may form
    small bubbles in rock

10
Igneous Rock (cont)
  • Composition of igneous rock is determined by
    chemical composition of magma.
  • 3 Families based on composition
  • Granite
  • Basalt
  • Diorite

11
Igneous Rock (cont)
  • Granite Family
  • Felsic magma high silica
  • Light color
  • Main minerals orthoclase feldspar quartz
  • Ex granite (intrusive)
  • rhyolite and obsidian (extrusive)

12
Igneous Rock (cont)
  • Basalt Family
  • Mafic lava low silica, high iron
  • Dark color
  • Main minerals plagioclase feldspar and augite
  • Ex basalt gabbro

13
Igneous Rock (cont)
  • Diorite Family
  • Medium colored
  • Main minerals plagioclase feldspar, hornblende,
    augite, and biotite.
  • Little or no quartz
  • Ex diorite andesite

14
Igneous Rock StructuresIntrusions underground
  • Batholith
  • Largest (cover over 100kmĀ²)
  • Form cores of many mountains
  • Stock
  • Similar to batholith but cover less area
  • Laccolith
  • Magma pushes overlying rock layer into an arc
  • May form dome mountains
  • Sills
  • Sheet of magma flows between layers of rock
    (horizontal)
  • Dikes
  • Magma flows upward through fractures and cut
    across rock layers vertically

15
Igneous Intrusions
16
Igneous Rock StructuresExtrusions at surface
  • Volcanic neck softer parts of volcanic cones
    wear away exposing solidified rock in vent.
  • Many are simply flat lava flows
  • Lava plateaus lava flows out long cracks in the
    surface
  • Cover vast areas
  • Fill in valleys and cover hills to form flat
    plateaus

17
Igneous Extrusions
18
Sedimentary Rock
  • Compaction and cementation form sedimentary rock.
  • Compaction weight of overlying sediments causes
    pressure that squeezes air and water out of
    sediments
  • Cementation water carries dissolved minerals
    through sediments which provide a cement to hold
    fragments together.
  • Sedimentary rocks are classified by the kind and
    size of their sediments.

19
Sedimentary Rock (cont)
  • Clastic sedimentary rocks
  • Rock fragments are carried by wind, water and ice
    become compacted and cemented together
    classified by size
  • Conglomerate rounded, gravel-sized pebbles
    cemented by minerals
  • Breccia gravel-sized fragments (angular with
    sharp edges)
  • Sandstones are made up of sand-sized grains
  • Major component quartz
  • Many are porous enough to allow liquids (water,
    crude oil) to move through.
  • Shale consists of clay-sized particles
  • Usually pressed into flat, flakey layers

20
Sedimentary Rock (cont)
  • Chemical Sedimentary Rock
  • Forms from minerals once dissolved in water
  • Minerals may precipitate out due to temperature
    changes
  • Evaporites form when water evaporates and leaves
    minerals behind

21
Sedimentary Rock (cont)
  • Organic Sedimentary Rock
  • Forms from remains of living things
  • Coal forms from dead plant remains buried and
    compacted
  • Limestone forms from the shells of marine
    organisms that use calcite
  • Chalk is limestone made of shells of one-celled
    marine organisms

22
Sedimentary Rock Features
  • Stratification layering occurs when type of
    sediment changes
  • May be due to change in river current, sea level,
    etc.
  • Thickness of layers (beds) depends on how long
    the sediment is deposited
  • Most water-deposited layers are horizontal
  • Wind-deposited layers may exhibit cross-bedding
  • Graded bedding different kinds sizes of
    material are deposited in the same layer as they
    settle out.

23
Sedimentary Rock Features (cont)
  • Ripple marks
  • Form from action or wind or water on sand.
  • Mud cracks
  • Muddy deposits dry and shrink causing shrinking
  • River flood plains, dry lake beds
  • When area floods new deposits fill in and
    preserve the cracks.

24
Sedimentary Rock Features (cont)
  • Fossils
  • The remains or traces of ancient plants and
    animals
  • Are preserved in sedimentary rock when remains
    are buried
  • Harder parts may remain but most often its only
    the impression

25
Sedimentary Rock Features (cont)
  • Concretions
  • Lumps or nodules of rock with a composition
    different from the main rock body
  • Precipitated minerals build up around existing
    rock
  • Geodes groundwater deposits dissolved quartz or
    calcite inside a cavity and crystals form

26
Metamorphic Rock
  • Changing from one type of rock to another by
    heat, pressure and chemical processes
    metamorphism
  • Minerals may change into other chemicals
  • Minerals may change size, shape, or separate into
    bands (layered look)
  • Hot fluids in magma may change mineral
    composition by dissolving some minerals and
    adding others

27
Metamorphic Rock (cont)
  • Two types of metamorphism
  • Contact metamorphism
  • Hot magma is near or touching rock
  • Changes structure and/or mineral composition
  • May also include hot chemical fluids working
    through fractures
  • Regional metamorphism
  • Occurs over large areas during tectonic activity
  • Plates moving against each other causes
    tremendous heat and pressure at the edges
    causes chemical changes in rock minerals
  • Most metamorphic rock is formed this way.

28
Metamorphic Rock (cont)
  • Classification is according to structure
  • Foliated
  • Visible parallel bands
  • Extreme pressure flattens mineral crystals into
    bands
  • Minerals of different densities may separate into
    bands -gt alternating light and dark

29
Metamorphic Rock (cont)
  • Common foliated rocks
  • Slate
  • Pressure on shale produces thin layers that split
    into sheets
  • Schist
  • Pressure on slate courser grained
  • Gneiss
  • Intense heat and pressure on schist -gt minerals
    separate into bands of different densities

30
Metamorphic Rock (cont)
  • Unfoliated
  • Rocks do NOT have bands of crystals
  • Quartzite sandstone is highly compacted
  • Marble compression of limestone
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