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Rocks: Materials of the Solid Earth Chapter 2 Earth Science, 6e Modified by Dr. Kane What is a Rock? How would you define a rock and a mineral? 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 The rock cycle (page 45) PART – I: IGNEOUS ROCKS FEEDBACK: From what process igneous rocks from? Origin of Magma (page 228) Magma forms at three major geological settings: • Divergent (mid ocean ridge) • Convergent (subduction zone) • Intra plate (hotspot) Origin of Magma (page 148) Mid Ocean Ridge (divergent) Subduction Zone (Convergent) Causes of Magma Formation Decompression Melting (opening a bottle of soda) Factors influencing magma formation: 1. Heat Increase 2. Reduction of confining Pressure 3. Increase in volatiles (gases) 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 Classification of Igneous rocks When identifying Igneous rocks look for: 1. Grain Size (TEXTURE) and 2. Rock color (CHEMICAL COMPOSITION) 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 Feedback: The slower the rate of cooling, the smaller / larger the crystals? 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) 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 Photomicrograph Photomicrograph What’s the texture? What’s the texture? What’s the texture? What’s the texture? What’s the texture? 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 Feedback • Which mineral crystallizes first? • Which mineral crystallizes last? Question • Can Olivine and Quartz be found together in the same rock? • Why? … 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 Granite (intrusive) or Rhyolite (volcanic) 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 midocean ridge, and the upper mantle • Common rock is Basalt (volcanic) or Gabbro (plutonic) Texture? Mafic or Felsic? Texture? Mafic or Felsic? 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%<SiO2 <60% • Common rock is Andesite (volcanic) or Diorite (intrusive) • Found mostly at Suduction Zone 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) Classification of igneous rocks PART – II: Sedimentary rocks FEEDBACK From what geological process sedimentary rocks form? 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) Frost wedging (page 55) Joint-controlled weathering in igneous rocks Unloading and exfoliation of igneous rocks 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 (CO2) dissolved in water forms carbonic acid and alters the material Factors of weathering Important factors • Climate (heat and moisture) • Chemical weathering is most effective in areas of warm temperatures and abundant moisture Chemical Weathering Weathering of granite minerals • Weathering of potassium feldspar produces clay Sedimentary Rocks Lithification: 1.Compaction of loose sediment through confining pressure of overlying rocks 2.Cementation of loose sediment by • Calcite • Silica • Iron Oxide 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 (Coarse grained) Classification of sedimentary rocks (page 59) Shale with plant fossils Sandstone Conglomerate Classifying sedimentary Rocks 2. Chemical Sedimentary rocks • Derived from material that was once in solution and precipitates to form sediment. Two groups: 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 Fossiliferous limestone 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 Rock salt 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 PART – III: Metamorphic Rocks FEEDBACK: • What process forms metamorphic rocks? • Where would you expect to find metamorphic rocks? • Florida or Georgia? Why? 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 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) Types of pressure (stress) in metamorphism Metamorphic Grades Degrees of metamorphism • Low-grade (where shale becomes slate) • Medium-grade (where granite becomes gneiss) • High-grade (rock partially melts → migmatite) Metamorphic Textures Nonfoliated from contact metamorphism Typical rocks: Marble and Quartzite Resembles a coarse-grained igneous rock Is localized around intrusion Marble – a Nonfoliated metamorphic rock Development of foliation due to directed pressure Gneiss typically displays a banded appearance Classification of metamorphic rocks 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) End of Chapter 3 1 - The Texture of an igneous rock is a. b. c. d. e. Shape of the crystals Size and arrangement of crystals How hard of soft the rock feels All of the above I have no idea 2 – Texture of igneous rocks is determined by a. b. c. d. e. Pressure and temperature Amount of sulfur in the magma Rate of cooling of magma Depth of cooling of magma c and d only 3 - The slower the rate of cooling, the … a. Smaller the crystals of the rock formed b. Larger the crystals c. No relation whatsoever 4 - Which terms characterize a basalt? a. b. c. d. Felsic/Light colored/silica rich Mafic/dark colored/silica poor Felsic/dark colored/silica rich Mafic/light colored/silica poor 5 - Name the volcanic rock (s) a. Granite b. Basalt c. Rhyolite d. Gabbro e. b and c 6 - Is this rock: a: Plutonic? Or b: Volcanic? 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 8 – Where to find a basaltic magma? a. b. c. d. e. On the continental crust mainly On the Oceanic crust At the mid-ocean ridge At subduction zone b and c 9 –Which texture indicates a magma rich in gases? a. b. c. d. e. Phaneritic Aphanitic Porphyritic Pyroclastic None of these 10 –Which texture indicates two rates of cooling? a. b. c. d. e. Phaneritic Aphanitic Vesicular Pyroclastic None of these 11 – Where to find a felsic magma? a. b. c. d. At mid ocean ridge On the ocean floor On the continental crust At subduction zone 12 –Which term means finegrained texture? a. b. c. d. e. Aphanitic Phaneritic Porphyritic Vesicular None of these 13 - Texture? a: Glassy Or b: Pophyritic 14 - Which texture means all coarse-grained rock? a. b. c. d. e. Aphanitic Porphyritic Phaneritic Glassy Vesicular 16 - Quartzite is what type of metamorphic rock? a. Regional metamorphism b. Contact metamorphism c. Not a metamorphic rock 81 17 – In what type of metamorphism do pressure and temperature work together? a. b. c. d. Contact metamorphism Regional metamorphism All of the above None of the above 82 18 - What is the parent rock of limestone? a. b. c. d. e. Quartzite Granite Marble Basalt This does not make sense 83 19 – Which one of these is a foliated metamorphic rock? a. b. c. d. e. Marble Granite Mica-schist Basalt Shale 84 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 21- What type of weathering is oxydation? a. Chemical weathering b. Mechanical weathering c. Soil sampling d. a and b e. None of the above 22 - Exfoliation results from a. Frost wedging b. Oxidation c. Unloading d. Thermal expansion e. None of the above 23 - Which one is the metamorphic rock? Do not take a. SANDSTONE for b. GRANITE (granted)! Have a c. GNEISS (nice) day! 88 THE END THAT’S ALL FOLKS! THANK YOU!!!