Soil Chemistry and Earth's Structure
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Questions and Answers

What is the primary structure of phyllosilicates based on?

  • Interconnected six member rings of SiO4-4 tetrahedra (correct)
  • Isolated octahedral units
  • Linear chains of silicon atoms
  • Single tetrahedral units

    • Talc is also known as soapstone.

    True

    What is the chemical formula of Talc?

    Mg3Si4O10(OH)2

    Phyllosilicates are also called __________ silicates.

    <p>sheet</p> Signup and view all the answers

    Match the following examples of phyllosilicates to their descriptions:

    <p>Muscovite = A type of mica that is light in color Biotite = A dark-colored mica mineral Chlorite = Has a characteristic green color Talc = Soft mineral used in talcum powder</p> Signup and view all the answers

    Which element has the highest percentage by mass in the earth's composition?

    <p>Oxygen</p> Signup and view all the answers

    Silicate minerals are compounds of metals combined only with oxygen and sulfur.

    <p>False</p> Signup and view all the answers

    What is the chemical formula for iron ore known as Hematite?

    <p>Fe2O3</p> Signup and view all the answers

    The _____ layer of the earth is mainly composed of rocks and minerals.

    <p>lithosphere</p> Signup and view all the answers

    Which of the following is considered a sulfide mineral?

    <p>Galena</p> Signup and view all the answers

    Match the following minerals with their type:

    <p>Hematite = Oxide Galena = Sulfide Corundum = Oxide Chalcopyrite = Sulfide</p> Signup and view all the answers

    What type of minerals are primarily composed of metals with silicon and oxygen?

    <p>Silicate minerals</p> Signup and view all the answers

    Carbonate minerals contain metals combined with carbon and oxygen.

    <p>True</p> Signup and view all the answers

    What is the main component of calcite?

    <p>CaCO3</p> Signup and view all the answers

    Physical weathering involves chemical reactions that change the composition of rocks.

    <p>False</p> Signup and view all the answers

    What term is used to describe the removal or transport of weathered rock materials?

    <p>erosion</p> Signup and view all the answers

    The organic remains, clay, and rock particles in the soil are collectively known as __________.

    <p>humus</p> Signup and view all the answers

    Match the types of weathering with their descriptions:

    <p>Physical weathering = Mechanical disruption of rocks Chemical weathering = Alteration of minerals through chemical reactions Biological weathering = Weathering caused by living organisms Weathering = Breakdown of rock minerals and rock masses</p> Signup and view all the answers

    Which of the following is NOT a type of weathering?

    <p>Weather events</p> Signup and view all the answers

    What is colloid in the context of soil?

    <p>Particles less than 0.001 mm</p> Signup and view all the answers

    The zone of leaching refers to the accumulation of minerals that have been washed down from above.

    <p>False</p> Signup and view all the answers

    Which of the following is a primary mineral found in sesquioxides?

    <p>Gibbsite</p> Signup and view all the answers

    Histosols are primarily composed of crystalline mineral structures.

    <p>False</p> Signup and view all the answers

    What are the two main components of sesquioxides?

    <p>Iron and aluminum oxides</p> Signup and view all the answers

    Histosols have a net charge that is always __________.

    <p>negative</p> Signup and view all the answers

    Match the following properties with their respective soil types:

    <p>Gibbsite = Aluminum oxide found in sesquioxides Humus = Organic soil colloids Goethite = Iron oxide found in sesquioxides Hydroxyl groups = Surface plane for ion adsorption</p> Signup and view all the answers

    Which mineral is a common constituent of Al-rich medium grade metamorphic rocks?

    <p>Muscovite</p> Signup and view all the answers

    Biotite is typically brown to black in color.

    <p>True</p> Signup and view all the answers

    What type of rock is chlorite commonly found in?

    <p>low grade metamorphic rocks</p> Signup and view all the answers

    Andisols are composed largely of _____ materials containing varying amounts of Al & Si.

    <p>vitric or glassy</p> Signup and view all the answers

    What is the characteristic shape of Allophane?

    <p>Spherule</p> Signup and view all the answers

    Imogolite tends to form inside glass fragments under conditions of high pH and Si concentration.

    <p>False</p> Signup and view all the answers

    Muscovite is characterized by its _____ to light brownish color.

    <p>white</p> Signup and view all the answers

    Match the following minerals with their descriptions:

    <p>Muscovite = White to light brown color, found in Al-rich metamorphic rocks Biotite = Brown to black color, common in trachytic volcanic rocks Chlorite = Common in low grade metamorphic rocks, green color Allophane = Characteristic spherule shape, forms inside glass fragments</p> Signup and view all the answers

    Study Notes

    Chemistry of Soil

    • Soil is the upper layer of Earth where plants grow.
    • It's a mixture of organic remains, clay, and rock particles.
    • Soil is formed from weathered rock by the action of climate and living organisms.

    Learning Objectives

    • Discuss different types of soil colloids and their properties.

    Geosphere

    • Greek: geo (earth), sphaira (globe).
    • The portion of the Earth that includes the interior, rocks, minerals, landforms, and processes shaping the surface.

    Structure of the Earth

    • Crust:
      • Varies in thickness (3-25 miles).
      • Thinner under oceans, thicker under continents.
      • Primarily granitic and mafic silicates.
      • Lithosphere (crust and top of mantle).
    • Mantle:
      • Thickest layer.
      • Asthenosphere (upper portion).
      • Mostly ultramafic silicates.
    • Core:
      • Two parts: outer (liquid) and inner (solid).
      • Mostly iron, nickel, and sulfur.

    Data on Earth's Interior

    • Density (g/cm³): Varies throughout the layers.
    • Thickness (km): Varies significantly.
    • Rock Types: Types of rocks found at different depths are listed.

    Elemental Composition of Earth's Surface

    • Element: Oxygen, Silicon, Hydrogen, Aluminum & others.
    • Atom %: Percentage of each element by atom count.
    • Mass %: Percentage of each element by mass.

    The Lithosphere: Organic and Inorganic

    • The lithosphere is primarily made up of rocks and minerals.
    • Silicate minerals: Compounds of metals with Si and O.
    • Carbonate minerals: Metals combined with C and O.
    • Oxide minerals: Metals combined with O only.
    • Sulfide minerals: Metals combined with S only.

    Some Non-silicate Minerals of Economic Importance

    • A table with mineral types, names, chemical formulas and source/use.

    Soil

    • The upper layer of earth where plants grow.
    • Typically black, dark brown, or reddish.
    • Mixture of organic remains, clay, and rock particles.
    • Weathered rock by climate and living organisms.

    Weathering and Erosion

    • Weathering: Breakdown of rock by the action of elements such as sun, wind, rain and organisms.
    • Types of Weathering:
      • Physical: Mechanical disruption (e.g., granular disintegration, exfoliation).
      • Chemical: Caused by OH-, mild acids, and water.
      • Biological: Due to vegetation, animals or microorganisms.
    • Erosion: Removal and transport of weathered rock.

    Soil Horizons

    • Layers within soil, each with distinct characteristics.
    • O Horizon: Surface litter.
    • A Horizon: Topsoil.
    • E Horizon: Zone of leaching (materials move downward).
    • B Horizon: Subsoil (accumulation of leached materials).
    • C Horizon: Weathered parent material.
    • R Horizon: Bedrock (unweathered parent material).

    Soil Colloids

    • Most active in soil, influencing physical and chemical properties.
    • Made up of:
      • Humus particles (organic colloids): Tiny organic matter particles.
      • Clay particles (inorganic colloids): Less than 0.002mm.
    • Only particles less than 0.001 mm are officially defined as colloids.

    Types of Soil Silicates

    • Crystalline silicates: Phyllosilicates (tetrahedral and octahedral crystal sheets).
    • Non-crystalline silicates: Andisols (amorphous clays).
    • Iron and aluminum oxides: Oxisols (e.g., gibbsite, goethite).
    • Organic colloids: Histosols (non-crystalline, long C-chain molecules).

    Phyllosilicates

    • Also called sheet silicates.
    • Group of minerals that includes micas, chlorite, serpentine, talc, and clay minerals.
    • Basic structure: interconnected six-membered rings of SiO4-4 tetrahedra.
    • Three out of four oxygens shared = basic structure of Si₂O5₂.
    • Most contain OH- ion at center of 6-membered rings = Si₂O₅(OH)₃

    Examples of Phyllosilicates

    • Talc (soapstone)
    • Mica group (muscovite, biotite)
    • Chlorite group

    Andisols

    • Non-silicate crystalline clays like allophane and imogolite.
    • Volcanic origin (chemically and mineralogically distinct).
    • Composed of vitric or glassy materials with Al & Si.
    • Lack a well-defined structure (amorphous), quite soluble.

    Sesquioxides or Oxisols

    • Iron and aluminum oxides (e.g., gibbsite, goethite).
    • Found in many soils, especially in warm humid regions.
    • Coordinated with O atoms (e.g., Al or Fe).
    • May form crystalline sheets or amorphous coatings.
    • Surface plane of covalently bonded hydroxyl groups strongly adsorb ions.

    Histosols

    • Organic soil colloids (non-crystalline).
    • Dominated by long C-chain molecules.
    • Important in nearly all soils.
    • Consist of long convoluted chains and rings of carbon bonded to H, O, and N.
    • High capacity to adsorb water.
    • Possess both positive and negative charges, but net charge is always negative.

    Rock Cycle

    • A continuous process involving the transformation of rocks.
    • Transitions between igneous, metamorphic, and sedimentary rocks.

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