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Rocks: Materials of the Solid Earth Chapter 2 Earth Science, 6e Modified by Dr. Kane.

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Presentation on theme: "Rocks: Materials of the Solid Earth Chapter 2 Earth Science, 6e Modified by Dr. Kane."— Presentation transcript:

1 Rocks: Materials of the Solid Earth Chapter 2 Earth Science, 6e Modified by Dr. Kane

2 What is a Rock? How would you define a rock and a mineral?

3 What types of Rocks are there?  Igneous Rocks: from magma or lava Origin: igneous activity Example: granite or basalt  Sedimentary rocks: from sediments Origin: weathering and erosion Example: sandstone or clay  Metamorphic rocks: from stress Origin: mountain building Example: gneiss or marble

4 The rock cycle (page 45)

5 PART – I: IGNEOUS ROCKS FEEDBACK: From what process igneous rocks from?

6 Plate Margins Divergent: Plates pull apart Example: Mid ocean ridge; Rift Convergent: Plate come together –Ocean – Continent; Ex: Cascades, Andes –Ocean – Ocean; Ex: Japan, Caribbean –Continent – Continent; Himalaya Transform Fault: Plates slide

7 Origin of Magma (page 228) Magma forms at three major geological settings: Divergent (Ex: Mid ocean ridge) Convergent (Ex: Cascades volcanoes) Intra plate Not a plate margin (Ex: Hawaii, Hot spot)

8 Origin of Magma (page 148)

9 Mid Ocean Ridge (divergent)

10 Subduction Zone (Convergent)

11 Causes of Magma Formation Decompression Melting (opening a bottle of soda) Factors influencing magma formation: 1. Heat Increase 2. Reduction of confining Pressure Role of volatiles (gases)

12 Types of Igneous rocks  Magma cools and crystallizes Inside the crust → Plutonic or Intrusive rocks  Lava cools and crystallizes Outside the crust → volcanic or extrusive rocks

13 Classification of Igneous rocks  When identifying Igneous rocks look for: 1.Grain Size ( TEXTURE) and 2.Rock color (CHEMICAL COMPOSITION)

14 Rate of Cooling and Crystal Size Texture is size and arrangement of crystals Crystal size is determined by the rate and depth of cooling of magma/lava Slow rate forms large crystals Fast rate forms microscopic crystals Very fast rate forms glass

15 Feedback: The slower the rate of cooling, the smaller / larger the crystals?

16 Types of Textures  Phaneritic: Coarse grain/slow cooling rate Example: Granite or Diorite  Aphanitic: Fine grain/fast cooling rate Example: basalt or rhyolite  Glassy: glasslike/very fast cooling rate Example: Obsidian (volcanic rock)

17 Types of Textures  Porphyritic: Slow then rapid cooling Example: porphyry basalt, porphyry granite  Vesicular: Full of holes due to gases Example: Vesicular basalt, scoria, and pumice  Pyroclastic: Angular volcanic fragments cemented by ash from violent eruptions Example: tuff

18 Photomicrograph


20 What’s the texture?





25 Obsidian Aztec

26 Temple Mayor, Mexico

27 Chemical Classification of Igneous rocks Bowen's reaction series (page 53): Minerals form in a systematic order through Discontinuous series (Olivine to Quartz) and Continuous series (Feldspars series) Magmatic Differentiation First to form settle at the bottom


29 Feedback Which mineral crystallizes first? Which mineral crystallizes last?

30 Question Can Olivine and Quartz be found together in the same rock? Why? …

31 Naming Igneous rocks  Granitic or Felsic rocks Light-colored rocks Rich in silica/poor in Fe and Mg Form from melting of continental crust Common rock is G ranite (intrusive) or Rhyolite (volcanic)

32 Naming Igneous rocks  Basaltic or Mafic/ultramafic Rocks Dark Rocks Rich in Fe and Mg/poor in silica Originate mostly from the oceanic crust at mid- ocean ridge, and the upper mantle Common rock is Basalt (volcanic) or Gabbro (plutonic)

33 Texture? Mafic or Felsic?


35 Naming Igneous rocks  Intermediate or Andesitic Rocks Mineral and chemical composition are average of felsic and mafic rocks Has dark minerals (pyroxene, amphibole, and mica) and light minerals (feldspar and quartz) Silica content: 50%

36 Naming Igneous Rocks  Ultramafic Rocks Dark rocks Very poor in silica: SiO2 <45% Originates from lower mantle and is found in oceanic floor at mid-ocean ridge along mafic rocks Typical rock is peridotite (intrusive) or Komatiite (volcanic)

37 Classification of igneous rocks

38 PART – II: Sedimentary rocks FEEDBACK From what geological process sedimentary rocks form?

39 Weathering  Two kinds of weathering 1. Mechanical weathering Breaking of rocks into smaller pieces Processes of mechanical weathering Frost wedging (freezing and thawing/exfoliation) Unloading (exposure to surface) Biological activity (burrow animals)

40 Frost wedging (page 55)

41 Joint-controlled weathering in igneous rocks

42 Unloading and exfoliation of igneous rocks

43 Weathering  Two kinds of weathering 2. Chemical weathering Alters the internal structures of minerals by removing or adding elements Most important agent is water Oxygen dissolved in water oxidizes materials Carbon dioxide (CO 2 ) dissolved in water forms carbonic acid and alters the material

44 Factors of weathering  Important factors Climate (heat and moisture) Chemical weathering is most effective in areas of warm temperatures and abundant moisture

45 Chemical Weathering  Weathering of granite minerals Weathering of potassium feldspar produces clay

46 Sedimentary Rocks  Lithification: 1.Compaction of loose sediment through confining pressure of overlying rocks 2.Cementation of loose sediment by Calcite Silica Iron Oxide

47 Classifying sedimentary rocks Two groups based on the source of the material 1.Detrital rocks (Residual solid material) Common rocks include Shale ( fine grained) Sandstone (medium grained) Conglomerate (round coarse grained) or Breccia (sharp coarse grain)

48 Classification of sedimentary rocks (page 59)

49 Shale with plant fossils

50 Sandstone

51 Conglomerate

52 Classifying sedimentary Rocks 2.Chemical Sedimentary rocks Derived from material that was once in solution and precipitates to form sediment. Two groups:

53 A – Chemical Organic Rocks  From biochemical processes; the most common sedimentary rocks: Example: Limestone is the most abundant chemical rock. Coal: from plants-peat-bituminous coal-lignite-anthracite

54 Fossiliferous limestone

55 B - Chemical Inorganic rocks  Chemical Sedimentary Rocks From precipitating solutions Evaporites: Salt or gypsum rocks, Through increase in concentration: Hematite, chert, flint, jasper, or agate

56 Rock salt

57 Features of Sedimentary rocks  Features of sedimentary rocks Strata, or beds (most characteristic) Bedding planes separate stratas Fossils Are traces or remains of prehistoric life Are the most important inclusions Help determine past environments Are used to determine age of sedimentary rocks Are used for rock correlation

58 PART – III: Metamorphic Rocks FEEDBACK: What process forms metamorphic rocks? Where would you expect to find metamorphic rocks? Florida or Georgia? Why?

59 Metamorphic rocks  Are changed from other rocks, including other metamorphic rocks “Every metamorphic rock has a parent rock “ Metamorphism occurs between 200C – 800C at several kms depth

60 Causes and Types of metamorphism?  Heat from magma → Contact metamorphism  Pressure (stress) → Regional metamorphism Confining pressure: from burial Differential stress: during mountain building Chemically active fluids Water and other volatiles (Hydrothermal fluids)

61 Types of pressure (stress) in metamorphism

62 Metamorphic Grades  Degrees of metamorphism Low-grade (where shale becomes slate) Medium-grade (where granite becomes gneiss) High-grade (rock partially melts → migmatite)

63 Metamorphic Textures  Nonfoliated from contact metamorphism Typical rocks: Marble and Quartzite Resembles a coarse-grained igneous rock Is localized around intrusion

64 Marble – a Nonfoliated metamorphic rock

65 Development of foliation due to directed pressure

66 Gneiss typically displays a banded appearance

67 Classification of metamorphic rocks

68 Resources from rocks and minerals  Nonmetallic mineral resources Make use of the material’s Nonmetallic elements Physical or chemical properties Two broad groups Building materials (e.g., limestone, gypsum) Industrial minerals (e.g., fluorite, corundum, sylvite)

69 End of Chapter 3

70 1 - The Texture of an igneous rock is a.Shape of the crystals b.Size and arrangement of crystals c.How hard of soft the rock feels d.All of the above e.I have no idea

71 2 – Texture of igneous rocks is determined by a.Pressure and temperature b.Amount of sulfur in the magma c.Rate of cooling of magma d.Depth of cooling of magma e.c and d only

72 3 - The slower the rate of cooling, the … a.Smaller the crystals of the rock formed b.Larger the crystals c.No relation whatsoever

73 4 - Which terms characterize a basalt? a.Felsic/Light colored/silica rich b.Mafic/dark colored/silica poor c.Felsic/dark colored/silica rich d.Mafic/light colored/silica poor

74 5 - Name the volcanic rock (s) a.Granite b.Basalt c.Rhyolite d.Gabbro e.b and c

75 6 - Is this rock: a: Plutonic? Or b: Volcanic?

76 7 – Porphyritic-aphanitic is what type of rock? a.Plutonic with two rates of cooling b.Volcanic with two rates of cooling c.None of these

77 8 – Where to find a basaltic magma? a.On the continental crust mainly b.On the Oceanic crust c.At the mid-ocean ridge d.At subduction zone e.b and c

78 9 –Which texture indicates a magma rich in gases? a.Phaneritic b.Aphanitic c.Porphyritic d.Pyroclastic e.None of these

79 10 –Which texture indicates two rates of cooling? a.Phaneritic b.Aphanitic c.Vesicular d.Pyroclastic e.None of these

80 11 – Where to find a felsic magma? a.At mid ocean ridge b.On the ocean floor c.On the continental crust d.At subduction zone

81 12 –Which term means fine- grained texture? a.Aphanitic b.Phaneritic c.Porphyritic d.Vesicular e.None of these

82 13 - Texture? a: Glassy Or b: Pophyritic

83 14 - Which texture means all coarse-grained rock? a.Aphanitic b.Porphyritic c.Phaneritic d.Glassy e.Vesicular

84 Quartzite is what type of metamorphic rock? a.Regional metamorphism b.Contact metamorphism c.Not a metamorphic rock

85 85 17 – In what type of metamorphism do pressure and temperature work together? a.Contact metamorphism b.Regional metamorphism c.All of the above d.None of the above

86 What is the parent rock of limestone? a.Quartzite b.Granite c.Marble d.Basalt e.This does not make sense

87 87 19 – Which one of these is a foliated metamorphic rock? a.Marble b.Granite c.Mica-schist d.Basalt e.Shale

88 20 -What type of weathering is frost wedging? a. Chemical weathering b. Mechanical weathering c. Soil sampling d. a and b e. None of the above

89 a. Chemical weathering b. Mechanical weathering c. Soil sampling d. a and b e. None of the above What type of weathering is oxidation?

90 22 - Exfoliation results from a. Frost wedging b. Oxidation c. Unloading d. Thermal expansion e. None of the above

91 Which one is the metamorphic rock? Do not take a.SANDSTONE for b.GRANITE (granted)! Have a c. GNEISS (nice) day!


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