Rock Cycle - Rocks (3B)
Pre Lab 

  • Comparing the forces of weathering.
  • Exploring agents of weathering.
  • erosion
  • grain
  • igneous
  • metamorphic
  • sedimentary

Students simulate weathering using a specimen of mud.


Weathering is the wearing away of rocks on the Earth’s surface by wind, water, ice, and heat. It is the first step in the formation of a sedimentary rock. Wind is responsible for wearing away rocks and creating great deserts like the Sahara Desert, Africa, an environment where water is not abundant. Water is responsible for wearing away of rocks in rivers, lakes, and the oceans. Ice is responsible for glacial erosion such as in Alaska, because as the ice moves, it carries rocks, which grind wears away the rocks beneath the glacier.

Climate also effects weathering. For example, in wet areas, water fills the cracks in rocks. When the temperature drops below freezing, the water in the cracks turns into ice. The ice expands, and forces the cracks apart. The ice then melts as the weather warms up. The rock thus becomes weaker and the crack wider with each successive freeze-thaw cycle. It eventually breaks apart into many pieces. Moreover, as a result of this process, concrete and asphalt in states like New York do not last as long as in warmer states like California.

As rocks are worn down by the weathering, broken pieces fall away from the parent rock and are further reduced in size through collisions with other rocks and additional weathering. Sand consists of small pieces of rock that have been eroded from a parent rock.

  1. Review the three major types of rocks with the students. Igneous or "hot rocks" are melted rocks that cool. Sedimentary or "wet rocks" are mainly formed by particles that are cemented together. Metamorphic or "changed rocks" are igneous, sedimentary or metamorphic rocks that chemically or physically change due to temperature and pressure.
  2. Explain that weathering is the first step in the formation of a sedimentary rock. Tell the students that there are many types of weathering.
  3. Demonstrate weathering by placing a hard piece of mud on a plate and squirting it with water. The water that hits the mud turns a dirty color. The mud loses pieces as the water penetrates the mud and loosens the particles.
  4. Give students an opportunity to examine the muddy water with a hand lens or microscope. Mud flakes will be easily visible. Mud particles are much smaller than sand particles. Sand is formed similarly because the agents of erosion (not just necessarily water alone ) eroded away pieces of rock from the "mother rock."

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