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 (A)

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 (B)</p> Signup and view all the answers

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

<p>False (B)</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 (A)</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 (A)</p> Signup and view all the answers

What is the main component of calcite?

<p>CaCO3 (D)</p> Signup and view all the answers

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

<p>False (B)</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 (D)</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 (B)</p> Signup and view all the answers

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

<p>Gibbsite (C)</p> Signup and view all the answers

Histosols are primarily composed of crystalline mineral structures.

<p>False (B)</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 (C)</p> Signup and view all the answers

Biotite is typically brown to black in color.

<p>True (A)</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 (B)</p> Signup and view all the answers

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

<p>False (B)</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

Flashcards

Soil Colloids

Tiny particles in soil with large surface areas, affecting soil properties like water retention and nutrient availability.

Silicate Minerals

Minerals primarily composed of silicon and oxygen, frequently combined with metals.

Carbonate Minerals

Minerals composed of carbon and oxygen, often combined with metals.

Oxide Minerals

Minerals composed of oxygen and metals.

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Sulfide Minerals

Minerals containing sulfur and metals.

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Hematite

An iron oxide mineral, often used as an iron ore and pigment.

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Magnetite

An iron oxide mineral with magnetic properties, used as an iron ore.

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Galena

A lead sulfide mineral, a key source of lead.

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Organic Colloids (Histosols)

Non-crystalline colloids primarily composed of long carbon chain molecules.

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Phyllosilicates

Sheet silicates, a mineral group including micas, chlorite, serpentine, talc, and clay minerals.

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Phyllosilicate Structure

Made up of interconnected six-membered rings of SiO4-4 tetrahedra forming extended sheets.

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Talc Formula

Mg3Si4O10(OH)2, a phyllosilicate mineral also known as soapstone.

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Talc Properties

Talc has a greasy feel, occurring in low-grade metamorphic rocks related to igneous rocks.

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Soil Profile

The different layers of soil, each with its own characteristics.

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Humus

Tiny pieces of organic matter in soil.

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Chemical Weathering

The breakdown of rocks by chemical reactions with water, acids, or other substances.

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Physical Weathering

The mechanical breakdown of rocks into smaller pieces without changing the chemical composition.

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Erosion

The transportation of weathered rock materials away from their original location.

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Clay

Soil particles smaller than 0.002 mm.

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Zone of Leaching

The upper soil layer where dissolved minerals are washed away.

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Sesquioxides

Iron and aluminum oxides found in many soils, especially important in highly weathered soils of warm humid regions. They consist of mainly either Al or Fe atoms coordinated with O atoms, forming crystalline sheets or amorphous coatings on soil particles.

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Gibbsite

A crystalline aluminum oxide (Al-oxide) found in sesquioxides, forming sheets.

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Goethite

A crystalline iron oxide (Fe-oxide) found in sesquioxides, forming sheets.

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Sesquioxide Colloid Adsorption

The surface plane of sesquioxides, composed of covalently bonded hydroxyl groups, enables strong adsorption of certain ions.

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Muscovite

A common mineral in medium-grade Al-rich metamorphic rocks, found in Al-rich igneous rocks, but not in volcanic rocks. It's white to light brownish.

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Biotite

Common in ultrabasic rock, trachytic volcanic rocks, granitic rocks, and metamorphic rocks. It's brown to black.

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Chlorite

A dark mineral with a complex formula, common in low-grade metamorphic rocks. It's green to pale yellow.

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Andisols

Soils rich in volcanic ash, composed of glassy materials like allophane and imogolite.

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Allophane

A poorly-ordered structure, early weathering product of volcanic glass, forms inside glass fragments. It's spherical.

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Imogolite

A poorly-ordered structure, early weathering product of volcanic glass, forms on the exterior of glass fragments. It looks thread-like.

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Volcanic Ash

A chemically and mineralogically distinct material compared to other soil parent materials, made of vitric or glassy materials with varying amounts of Al and Si.

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What are the key differences between allophane and imogolite?

Allophane forms inside glass fragments, where Si concentration and pH are high. Imogolite forms on the exterior of glass fragments, where pH and Si concentration are lower. Allophane has a spherical shape, while imogolite has a thread-like morphology.

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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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Chemistry of Soil (CHM031) PDF

Description

Explore the fascinating chemistry of soil, including its composition and the different types of soil colloids. Delve into the geosphere and learn about the structure of the Earth, from the crust to the core. Understand how various components shape our planet's surface.

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