Rocks and their Formation

Rocks and their Formation:

Igneous Rocks

Rocks deep inside the Earth may become hot enough to partially melt. Molten rock is called magma. It may stay inside the Earth, or it may erupt onto the surface as lava. When molten rock cools down it solidifies and becomes solid rock. Rocks formed this way are called IGNEOUS ROCKS

There crystals interlock.

The size of the crystals depends on the rate at which the magma or lava cools. E.g.Granite

Sedimentary Rocks

Rock that has formed through the deposition and solidification of sediment.
Examples: sediment transported by water (rivers, lakes, and oceans), ice ( glaciers), and wind.
Sedimentary rocks are often deposited in layers, and contain fossils

Metamorphic Rocks

The action of heat and/or pressure can change rocks, causing new crystals to form. These changed rocks are called Metamorphic Rocks.

Example: Marble is a metamorphic rock formed from chalk or limestone. The grains in chalk and limestone are weakly joined together with small gaps between them. When marble forms, the grains become new crystals of Calcium Carbonate that interlock tightly.

Erosion

Sedimentary rocks are more likely to erode than igneous and metamorphic rocks. This is because metamorphic and igneous rocks have interlocking crystals

Key words:

Magma
Lava
Solidifies
Igneous Rocks
Crystals
Granite
Erosion
Sediment
Fossil
Metamorphic
Marble


Questions:

1. Name an example of a igneous rock.
2. Why are fossils often found in sedimentary rocks not igneous?
3. What is erosion?


What you should know:

• 2.1 Be able to Be able to describe that igneous rocks, such as granite, are:
  • a) formed by the solidification of magma or lava
  • b) made of crystals whose size depends on the rate of cooling
• 2.2 Be able to describe chalk and limestone as examples of sedimentary rocks.
• 2.3 Be able to describe how sedimentary rocks are formed by the compaction of layers of sediment over a very long time period.
• 2.4 Know and understand that sedimentary rocks:
  • a) may contain fossils
  • b) are susceptible to erosion
• 2.5 Be able to describe marble as an example of a metamorphic rock.
• 2.6 Be able to describe the formation of metamorphic rocks by the action of heat and/or pressure, including the formation of marble from chalk or limestone.
• 2.7 Know and understand that limestone, chalk and marble exist in the Earth’s crust and that they are all natural forms of calcium carbonate.