The Rock Cycle

According to the CSEC Syllabus, the specific objectives related to Volcanoes are as follows:

1. Describe the formation of the three types of rocks.

As such, we will follow these objectives for this unit.

WHAT IS THE ROCK CYCLE?

The rock cycle is the effectively the term used to describe the constant change of state that rocks undergo due to various processes such as weathering, erosion, transportation and deposition. It can be seen as a recycling process because the rocks simply go from one state to the next repeatedly over long periods of time.

Types of Rocks

There are three types of rocks that make up the Earth's crust:

• Igneous Rocks - These rocks are formed from the cooling of magma either below (intrusive) or above the surface (extrusive). These rocks are crystalline or usually hard and resistant to erosion. Examples of igneous rocks include: granite (intrusive) and basalt (extrusive).

• Sedimentary Rocks - Overtime, the accumulation of sediments (most commonly in the oceans) forms what we call sedimentary rocks. These rocks are weaker and more easily eroded. These rocks form layers or beds so when broken in half, they may have various colors or groves showing their layers. Examples of sedimentary rocks include: sandstones, limestones, coal, siltstone and shale.

• Metamorphic Rocks - these rocks have undergone change as a result of intense heat or pressure. These rocks are extremely strong, resistant to erosion and even form mountain ranges in many parts of the world. Examples of metamorphic rocks include: slate (formed from shale and used as roofing), quartzite (from sandstone) and marble (from limestone).