Presentation on theme: "Rocks: Materials of the Solid Earth Chapter 2 Earth Science, 6e Modified by Dr. Kane."— Presentation transcript:
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
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)
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
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 G ranite (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 mid- ocean ridge, and the upper mantle Common rock is Basalt (volcanic) or Gabbro (plutonic)
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%
"name": "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%
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)
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)
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
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 (round coarse grained) or Breccia (sharp coarse grain)
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
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)
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)