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What Types of Rock Is Soil Made Of?

A fistful of soil may appear as an uninteresting clump of dull or sandy-colored dirt. On a microscopic level, however, soil teems with tiny organic and inorganic matter. Dead and decomposing plants and animals slowly break down into the soil, giving soil its dark and loamy texture. Intermixed with organic matter are varying amounts of inorganic matter: small molecules of water and air mixed with tiny grains of rocks and minerals. The types of rocks in soil are classified into three main categories: igneous, metamorphic and sedimentary. These different types of rocks contribute to the soil's varying texture and consistency and affect the soil's ability to support plant life. Fresh, new rock is always replenishing the soil through remarkable natural processes called weathering and erosion.

  1. Formation of Soil

    • Soil is formed through weathering and erosion, the processes that break down solid rock into tiny pieces. Weathering is the physical or chemical process that breaks down rock. Wind, moving water, precipitation, ice, heat, geologic movement, burrowing animals and plant roots all contribute to the weathering of rock. Erosion moves the weathered material across the Earth. Floods, wind and other means carry the tiny particles of rock across the land. Mixed with varying combinations of organic and inorganic matter, soil texture may be sandy, silty or clay. Sandy soil contains more rock particles than organic matter; silty soil contains more organic matter; clay soils contain more water than sandy or silty soils.

    Igneous

    • Igneous rock constitutes the majority of the Earth's crust and is the basis for the two other types of rock. Also called volcanic rock since it comes from lava, igneous rock is rich in nutrients, replenishing the soil with the necessary minerals iron, magnesium, calcium and more. Scientists classify igneous rock into two main categories, basaltic and granitic. Basaltic igneous rock is lava that has cooled near the surface of the Earth and is therefore softer and more susceptible to weather and erosion. Granitic rock cools deep with the Earth's crust and is much harder and less rich in nutrients. Examples of igneous rock include basalt, granite, pumice and feldspar.

    Metamorphic

    • Metamorphic rock is rock that has undergone a change in chemical structure, called metamorphosis. This type of rock was once igneous or sedimentary rock that underwent intense heat or pressure that altered its chemical composition. Scientists classify metamorphic rock based on the type of process that formed the rock. Metamorphic rock produced from heat is further classified as contact metamorphic rock. Regional metamorphic rock is metamorphic rock produced from pressure. Examples of metamorphic rock include marble, slate, gneiss and quartzite.

    Sedimentary

    • Sedimentary rock is a hardened amalgam of inorganic and organic material. Typically found in the shallower, low-lying areas of the Earth's crust, sedimentary rock forms when crushed deposits of igneous or metamorphic rock mix with organic matter. The mixture solidifies and hardens through pressure or heat. Unlike metamorphic rock, sedimentary rock does not change chemically. Sedimentary rock is the most easily crushed and eroded type of rock. Examples of sedimentary rock include limestone, shale, sandstone, siltstone and gypsum.

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Soil
  1. What Is Limestone Rock?
  2. What Is Burnt Soil?
  3. What Is Arid Soil?
  4. What Is Soil Swelling?
  5. What Is Humus Fertilizer?
  6. Model Soil Types
  7. Soil Types & Weeds
  8. What Types of Soil Conduct Electricity?
  9. What Are the 10 Different Types of Soil?
  10. What Is Soil Texture?
  11. What Types of Soil Do Beans Grow In?
  12. What Types of Soil Do Cacti Need?

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