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Igneous Rock Formation
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Igneous Rock Formation

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Questions and Answers

What is the characteristic shape of the aggregates in pillow structure?

  • Ovoid (correct)
  • Irregular
  • Cylindrical
  • Spherical
  • What is the term for the change in a rock's mineralogy, texture, and/or composition that occurs predominantly in the solid state?

  • Weathering
  • Metamorphism (correct)
  • Erosion
  • Diagenesis
  • What is the effect of increasing temperature on sedimentary or volcanic rocks?

  • Complete melting of minerals
  • Increased grain size of minerals (correct)
  • Decreased grain size of minerals
  • No change in grain size of minerals
  • What type of pressure is responsible for increasing pressure with depth in the Earth's interior?

    <p>Litho-static pressure</p> Signup and view all the answers

    What is the result of a rock being heated to a temperature at which a particular mineral is no longer stable?

    <p>Reaction that consumes the unstable mineral and produces new minerals</p> Signup and view all the answers

    What is the term for the fluid phase present in most metamorphic rocks at depth?

    <p>Metamorphic fluid</p> Signup and view all the answers

    What is the primary cause of devolatilization reactions in metamorphic rocks?

    <p>Increase in temperature</p> Signup and view all the answers

    What is the characteristic feature of the crust or rind of the ovoid masses in pillow structure?

    <p>Thick and vesicular</p> Signup and view all the answers

    What is the primary agent responsible for the formation of pillow structure?

    <p>Rapid chilling of highly fluid lava</p> Signup and view all the answers

    What is the result of the reaction that consumes unstable minerals and produces new minerals in metamorphic rocks?

    <p>Formation of a new mineral assemblage</p> Signup and view all the answers

    Study Notes

    Igneous Rocks

    • Igneous rocks can form in two environments: intrusive (plutonic) and extrusive (volcanic)
    • Intrusive rocks form below the surface of the earth, where temperatures are higher and cooling is slower, resulting in coarse-grained textures
    • Extrusive rocks form on the surface of the earth, where temperatures are lower and cooling is faster, resulting in fine-grained textures

    Types of Intrusions

    • Dikes: small, shallow intrusions that show a discordant relationship to the surrounding rocks
    • Sills: small, shallow intrusions that show a concordant relationship to the surrounding rocks
    • Laccoliths: larger intrusions that result in uplift and folding of the surrounding rocks
    • Plutons: bulbous bodies of magma that form deeper in the earth
    • Batholiths: larger bodies formed by the coalescence of many plutons

    Classification of Igneous Rocks

    • Based on silica content: basic (45-52%), intermediate (52-66%), and acidic (more than 66%)
    • Basic rocks: characterized by calcium-plagioclase, augite, and olivine
    • Intermediate rocks: characterized by quartz, orthoclase, plagioclase, biotite, and hornblende
    • Acidic rocks: characterized by quartz and feldspars

    Classification Based on Depth of Formation

    • Plutonic: formed at considerable depth, with slow cooling and coarse-grained textures
    • Hypabyssal: formed at intermediate depth, with faster cooling and medium-grained textures
    • Volcanic: formed at the surface, with rapid cooling and fine-grained textures

    Common Structures of Igneous Rocks

    • Pillow structure: formed by rapid chilling of highly fluid lava, characterized by ovoid masses with a thick vesicular crust and a coarser-grained interior

    Metamorphism

    • Refers to changes in a rock's mineralogy, texture, and/or composition that occur in the solid state
    • Caused by metamorphic agents: temperature, pressure, fluid, and state of stress

    Metamorphic Agents

    • Temperature: promotes recrystallization, increases grain size, and can lead to devolatilization reactions
    • Pressure: increases with depth, leading to litho-static pressure and confining pressure
    • Fluid: plays a crucial role in metamorphic processes, often present as an intergranular fluid phase

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    Description

    Learn about the two environments of igneous rock formation: intrusive/plutonic and extrusive/volcanic. Discover how temperature and cooling rates affect the type of rocks formed.

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