Chapter 3 – Rocks 3.1 The Rock Cycle Text pp 66 - 69

Rocks and Minerals Quick! – what ingredients go into a chocolate cake?

Just as ingredients - like eggs, flour, sugar and chocolate - go into baking a chocolate cake, so do minerals combine to form rocks. A rock is any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet.

There are three major types of rocks: Metamorphic rocks Igneous rocks Sedimentary rocks

Before looking at each group of rocks, we will look at a model for the rock cycle, which is the process that shows the relationships between the rock groups.

The Rock Cycle Interactions among Earth’s water, air and land can cause rocks to change from one type to another. The continuous processes that cause rocks to change make up the rock cycle.

Magma – Igneous Rock’s “Parent” Magma is molten material that forms deep beneath Earth’s surface. Magma that reaches the surface is called lava. When magma cools and hardens beneath the surface or as a result of a volcano eruption, igneous rock forms.

Weathering Any rock at Earth’s surface will undergo weathering. Weathering is the process in which rocks are physically and chemically broken down by water, air, and living things..

Weathered pieces of earth materials are called sediments Weathered pieces of earth materials are called sediments. Beach sand is an example of a large collection of sediment.

Eventually, sediments are compacted and cemented to form sedimentary rock.

Under extreme pressure and temperature conditions, sedimentary rock will change into metamorphic rock.

And back to magma… Finally, if metamorphic rocks undergo even more pressure or higher temperatures, they may melt to form magma…

Alternate Paths This path we just talked about is only one of many paths that rocks may take in the rock cycle. For example - A deeply buried igneous rock could change into metamorphic rock without becoming sediment first. A sedimentary rock could weather and form yet another sedimentary rock.

Where does the energy that drives the rock cycle come from? Processes driven by heat from Earth’s interior are responsible for forming both igneous and metamorphic rocks. Weathering and the movement of weathered materials are external processes powered by energy from the Sun. External processes produce sedimentary rocks.