Rocks I (Junior Cert Geography): Revision Notes

Rocks I

The Rock Cycle

The rock cycle explains how rocks on Earth are constantly being formed, broken down, and changed over time. There are three main types of rocks: igneous, sedimentary, and metamorphic. Each type can change into another over millions of years through different processes.

1. Igneous Rocks: These are the first types of rocks formed on Earth. They are created from cooled magma or lava.
2. Sedimentary Rocks: Over time, weathering and erosion break down rocks into small pieces called sediments. These sediments are transported by rivers, ice, and wind before being deposited in layers, where they are compacted into sedimentary rocks.
3. Metamorphic Rocks: When sedimentary or igneous rocks are subjected to intense heat and pressure, they change into metamorphic rocks.
4. Sometimes, rocks melt back into magma, and the cycle begins again.

Types of Rocks

• Igneous Rocks
  • Formation: Formed from hot molten magma or lava that cools and solidifies.
  • Examples:
  • Granite: Forms when magma cools slowly beneath the Earth's crust. Found in the Wicklow Mountains.
  • Basalt: Forms when lava cools quickly on the Earth's surface. Found at the Giant's Causeway in Co. Antrim.
  • Texture: Can be rough (Granite) or smooth (Basalt).

Basalt at the Giant's Causeway

• Sedimentary Rocks
  • Formation: Made from sediments, such as sand or shells, that are compressed over time into solid rock layers called strata.
  • Examples:
  • Limestone: Formed from compressed remains of sea creatures, found in the Burren, Co. Clare.
  • Sandstone: Formed from compressed layers of sand, found in Co. Cork and Co. Kerry.
  • Texture: Ranges from smooth to rough.

Limestone at the Burren

• Metamorphic Rocks
  • Formation: Created when existing rocks (igneous or sedimentary) are changed by intense heat and pressure.
  • Examples:
  • Marble: Formed from limestone that has been heated and compressed, found in Connemara.
  • Quartzite: Formed from sandstone that has been heated and hardened, found in the Sugarloaf Mountain, Co. Wicklow.
  • Texture: Usually smooth and harder than the original rocks.

Metamorphic rocks on Ireland's east coast