An Introduction to the Rock Cycle Rocks There are three (3) main types of rocks: Rocks can be igneous, sedimentary, or metamorphic. Igneous Rocks o Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive (volcanic) rocks. Granite is an igneous rock Sedimentary Rock Sedimentary rock is formed in three main ways: 1. 2. 3. by the deposition of the weathered remains of other rocks (known as clastic sedimentary rocks) by the deposition of the results of biogenic activity by precipitation from solution Limestone and shale are both types of sedimentary rock Metamorphic Rock Slate is a type of metamorphic rock Metamorphic rock is the result of the transformation of a pre-existing rock type. Metamorphic means "change in form“. Heat and Pressure physically and chemically The Rock Cycle Weathering • Weathering is the process of decomposition and/or disintegration of rocks, soils and their minerals through natural, chemical, and biological processes. Erosion • Erosion is the displacement of solids (soil, mud, rock, and other particles) because of wind, water, ice, gravity, or living organisms. • Deforestation, overgrazing, and road or trail building are human activities that can lead to erosion. physical weathering Frost heaving • Frost heave is the result of pressure created from a combination of freezing temperatures and soil defrosting. The fluctuating freezing and thawing conditions heave, or lift, the soil, which is often characterized by deep cracking of the soil. Plants may be uprooted from the ground as well. Frost wedging • • • • Frost wedging is caused by the repeated freeze-thaw cycle of water in extreme climates. Most rocks have small cracks in them, called joints. When it rains, rainwater seeps into these joints. As the day cools and temperatures at night drop below freezing, the water inside the joints freezes. As water freezes into ice, it expands. The expanding ice places pressure on the joints in the rock. Finally, when the pressure is too much, the joint expands. In some cases, the rock will split, though this usually happens after repeated freeze and thaws. As new water is added during the warmer days, more ice is created at night, wedging the joints apart further. physical weathering Plant roots Friction and impact • The roots of large plants can penetrate the rocky soil and break it apart. • Constant exposure to friction and impact can change the formation of the rocks and cause them to break off. physical weathering Animals Temperature changes • Animals that burrow into rocks can cause weathering. • The changing temperatures can alter landscapes by causing the soil to freeze or burn.