SOILS-1_Topic-2

Soil Formation and Development

Prepared by: JAN MICAH MANAMAN

Rock and Its Characteristics

  • Definition of Rock:

    • Solid material in the Earth's crust, about 10-25 miles thick.

    • Aggregate of two or more minerals.

    • Naturally formed solid material of minerals.

  • Petrology: Study of rocks.

Characteristics of Rock

  1. Texture:

    • Size and shape of the mineral crystals or grains.

    • Examples: coarse, fine, or glassy texture.

  2. Structure:

    • Arrangement of minerals or grains in a rock.

Classification of Rocks

Three General Classifications:

  1. Igneous Rock:

    • Formed from the solidification of magma (900-1600 °C).

    • Magma: Hot molten material inside Earth; Lava: Magma on the surface.

    • Types:

      • Intrusive:

        • Forms inside Earth; coarse-grained texture due to slow cooling.

        • Example: Granite.

      • Extrusive:

        • Forms from lava; fine-grained texture due to rapid cooling.

        • Examples: Basalt, Obsidian, Rhyolite.

Common Igneous Rocks

  • Granite: Light-colored, large-grained.

    • Composed of quartz, feldspar, mica.

  • Andesite: Fine-grained, mainly plagioclase.

  • Obsidian: Volcanic glass, rapid cooling prevents crystal formation.

  • Pumice: Light-colored vesicular rock from rapid solidification.

  • Basalt: Dark-colored, fine-grained, composed of plagioclase.

Sedimentary Rock

  • Formation: Formed from the compaction and cementation of sediments.

  1. Compaction: Pressure reduces volume, layering sediments.

  2. Cementation: Minerals deposited between sediments, hardening them.

Types of Sedimentary Rocks

  1. Clastic Rock: Formed from cemented sediments, typically broken bits of rock.

  2. Chemical Rock: Formed from dissolved minerals, like rock salt.

  3. Organic Rock: Formed from remains of living organisms, like coal and limestone.

  • Example: Coal - formed from ancient plants in swamps.

Common Sedimentary Rocks

  • Limestone: Composed mainly of calcite (CaCO3).

  • Shale: Made of fine clay particles, breaks into thin pieces.

  • Sandstone: Composed of cemented sand grains.

Metamorphic Rock

  • Formation: Changes from igneous or sedimentary rocks under heat and pressure (100-800 °C).

  • Types of Metamorphic Rock:

  1. Foliated Rock: Minerals arranged in parallel layers.

    • Example: Schist, Gneiss.

  2. Non-foliated Rock: Lacks layers, does not break into sheets.

    • Example: Marble, Quartzite.

Components of Soil Formation

Five Factors of Soil Formation

  1. Parent Material:

    • Source of soil, could be bedrock or organic material.

    • Two classifications: Primary (develops in-situ) and Secondary (transported).

  2. Climate:

    • Influences weathering and soil formation speed (temperature, rainfall).

  3. Organisms:

    • Affect decomposition and organic content.

  4. Relief (Topography):

    • Location impacts water movement and soil accumulation.

  5. Time:

    • Soil changes over time; takes 800-1000 years for 2.5 cm of fertile soil.

Stages of Soil Development

  1. Initial Stage: Unweathered parent material.

  2. Juvenile Stage: Beginning weathering.

  3. Virile Stage: Clay content increases; more minerals decompose.

  4. Senile Stage: Most resistant minerals survive.

  5. Final Stage: Complete soil development.

Soil Profile

  • Definition: Vertical section of soil showing distinct layers or horizons.

Horizons:

  1. Horizon O: Organic material (humus).

  2. Horizon A: Topsoil, rich in minerals and organic matter.

  3. Horizon E: Leached layer, concentrated sand/silt.

  4. Horizon B: Accumulation of minerals leached from above layers.

  5. Horizon C: Parent material from which the soil developed.

  6. Horizon R: Bedrock, underlying material.

Properties of Minerals

  • Over 2000 identified minerals; unique characteristics include:

    • Color: Not reliable for identification; example: Quartz varies in color.

    • Luster: Metallic or non-metallic.

    • Hardness: Defined by Moh's scale (1-10, talc to diamond).

    • Streak: Color of the powdered form.

    • Cleavage: Breakage along smooth planes.

    • Acid Reaction: Reaction with dilute acid for carbonates.

    • Specific Gravity: Ratio of weight of mineral to weight of equal water volume.

    • Crystal Form: Shape of mineral crystals based on atomic arrangement.

Weathering

  • Definition: Breakdown of rocks into smaller pieces.

Types of Weathering

  1. Physical Weathering:

    • Changes physical structure without altering chemical composition.

  2. Chemical Weathering:

    • Alters chemical structure; weaker products formed.

Physical Weathering Subtypes

  • Frost Action: Repeated freezing/thawing; expands and exerts force.

  • Extreme Temperatures: Causing expansion and contraction, leading to cracks.

  • Biological Activity: Plants and animals contribute to rock breakdown.

Chemical Weathering Processes

  • Hydrolysis: Water reacts, destroying original structure.

  • Carbonation: Carbonic acid reacts with minerals, enhancing solubility.